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IAEI News provides educational forums, updates on electrical codes and reports of innovative research to facilitate the development and enforcement of practices designed to drive efficiency and compliance with the highest standards of product development and safety—for the public as well as for electrical personnel. The magazine reaches authorities with power of product specification, approval and acceptance. Published six times a year by the International Association of Electrical Inspectors.

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Speed Control of Motors — An Introduction to Variable-Frequency Drives

Posted By Stephen J. Vidal , Tuesday, January 01, 2013
Updated: Thursday, December 13, 2012

Speed, torque, and horsepower are three interrelated parameters in motor control. The speed of a motor measured in revolutions per minute (RPM) defines a motor’s ability to spin at a rate per unit time. The torque of a motor measured in foot-pounds (ft-lb) is a rotational characteristic of the motor that is the algebraic product of force multiplied by distance. Electrically, one horsepower (hp) is equal to 746 watts. What is interesting about these motor parameters is that if you change one of the three variables, the other two are affected. For example, if you increase horsepower while keeping speed constant, torque increases.

An electric motor is a device that converts electrical energy into mechanical energy. An electrical signal is applied to the input of the motor and the output of the motor produces a defined amount of torque related to the characteristics of the motor. It is important to understand speed-torque characteristic curves as they show the relationship between speed as a percent of rated speed versus load torque as a percent of full rating. Motors are available in multi-speed configurations that can provide constant torque variable horsepower, constant horsepower variable torque, and variable torque variable horsepower.

Equation 1. Synchronous speed

Equation 1. Synchronous speed

Traditionally, dc motors have been used in precise speed control applications because of their ability to provide acceleration and deceleration from a dead stop position to full speed fairly easily. In a dc series motor (the field is in series with the armature), the speed is controlled by increasing or decreasing the applied voltage to the series field or armature by means of a field rheostat or an armature rheostat. Silicon controlled rectifiers (SCRs) have replaced rheostats as they can control large blocks of power without the heat dissipation problems of carbon or wire-wound variable resistors. Additionally, SCRs are much smaller in size than their earlier counterparts and interface well with programmable logic controllers.

The AC squirrel cage induction motor is essentially a constant speed device. The speed of the rotating magnetic field is referred to as synchronous speed. Equation 1 relates the synchronous speed (S) to the incoming line frequency (F) and number of poles (P) the machine is constructed of: [S = 120(F) ÷ P].

Here’s an example to illustrate this point. In the United States, the line frequency is 60 Hertz. A four-pole AC squirrel cage induction motor would therefore have a synchronous speed of 1800 RPM [(120 x 60) ÷ 4]. In practice, the motor will run at less than 1800 RPM as load is placed on the rotor. This difference in speed between synchronous speed and full-load speed is referred to as slip and is usually expressed as a percentage. Note that the only two variables in equation 1 that define speed are the incoming line frequency and the number of poles in the machine. Since the number of poles in a machine is fixed, the only variable that is left to change is the incoming line frequency. This is the basis for the operation of a variable-frequency drive (VFD).

It is important to understand the difference between the AC and the DC machine at this point. Earlier, we mentioned that a DC machine could have its speed changed by increasing or decreasing the applied voltage. This is not the case for an AC motor. In fact, you can damage an AC squirrel cage induction motor if you vary the incoming supply voltage.

The term variable-frequency drive is often used interchangeably with AC drive, inverter, or adjustable- frequency drive (AFD). The two most common circuits for adjusting the speed of an AC squirrel cage induction motor are the inverter and the cycloconverter.

The VFD using an inverter does two things: first, it takes the incoming AC signal and converts it to a DC signal through a process known as rectification, and then it takes the rectified DC signal and inverts it back to a variable voltage and variable-frequency AC signal. An inverter takes a waveform like a rectified DC signal and generates an equivalent time-varying waveform resembling a sinusoid. A block diagram for an inverter type VFD is shown in figure 1.

Figure 1. Block diagram of PWM VFD

Figure 1. Block diagram of PWM VFD

The VFD using a cycloconverter is a device that produces an AC signal of constant or controllable frequency from a variable-frequency AC signal input. The output frequency is usually one-third or less than the input frequency. The cycloconverter type of VFD is normally used with larger motors or groups of motors at once.

Typical specifications you might encounter with an inverter-type VFD are listed below:

Horsepower: 1–10 HP @ 230V

Input frequency: 50/60 Hz

Output frequency: 0–120 Hz standard; 0–400 Hz jumper selectable

Frequency setting potentiometer: 10 K ½ W

Ambient temperature: 0 – +40° C

Control method: PWM (pulse width modulation)

Transistor type: IGBT (insulated gate BJT)

Analog outputs: assignable

Digital Outputs: opto-isolated assignable

Terminal strips present on the VFD allow the device to interface to the outside world to familiar switching devices like start, stop, forward run, and reverse run. Instead of using a three-wire control circuit to start and stop a motor with momentary contact devices, the electronics of the drive control all those familiar operations.

Normally, the VFD also has a backlit liquid crystal display (LCD) that shows a variety of motor operational parameters that are fully programmable by the user. Solid-state devices like the silicon controlled rectifier, triac, and insulated gate bipolar junction transistor have allowed the variable-frequency drive to become the method of choice for AC motor speed control.


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Tags:  Featured  January-February 2013 

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Gratitude — The Path to Excellence

Posted By Steve Foran, Tuesday, January 01, 2013
Updated: Thursday, December 13, 2012

After one of my gratitude workshops, a business owner remarked, "If I let my staff know that I am grateful for their performance when they fall short of a goal, I am basically giving them permission to underperform. And I just cannot allow that because we will never grow or achieve our stretch goals.”  

I did not offer up a good response and his comments sent me searching for a better answer.

Here goes…

Genuine gratitude is not about accepting mediocrity. Fundamentally, gratitude is the feeling you experience when you attribute the positive aspects of your life to others. However, the state of gratitude is not limited to when things are good — but at the same time it is critical to understand that gratitude is not a Pollyanna masquerade for when things are bad simply to make them appear good.

Although gratitude is a foundation for happiness, it is not pixie dust that makes everything pleasant, at least not immediately. Genuine gratitude acknowledges the truth and sees reality for what it truly is — the good and the bad — it just allows you to do so from an appreciative perspective. This can be difficult and at times, it is near impossible.

Being appreciative about less desirable situations is tough because it is easy to focus on the negative aspects of the situation or it can be just as easy to gloss over the challenges and whitewash them with unbridled optimism. Or, as in the case of the bottom-line focused workshop participant, it can be perceived as accepting a life of mediocrity.

My response to the comments at that workshop was weak. In fact, it was somewhat embarrassing. As I drove away I wished I had said something else.

Then the analogy appeared. As a young engineer I was responsible for implementing a quality program in a large organization. Like all quality programs, we strived for continuous improvement. When mistakes were made, we jumped on them to learn — not just to fix the problem but, more importantly, to prevent the mistake from ever happening again. The investigations sought to inform not to blame.

After the investigation, we would learn something about what caused the error and we always found that some parts of our process were working just fine. Using this approach, we learned from our shortcomings and celebrated what we did well. This was our path to excellence and it was anything but mediocrity. In hindsight, we could have called them gratitude investigations.

Whether it is in your personal or professional life, gratitude actually transforms "accepting mediocrity” into "chasing excellence.” The systematic practice of gratitude parallels how one would investigate a non-conformance in a quality program. Both ideas are rooted in accepting and appreciating reality, but not for the sake of being stuck in that reality. Instead, they both know that future success is built upon the success of the current reality and what can be learned about the current reality. If you can obtain this mindset about your current reality, even if it is horrible, you’ll realize that your current reality is actually a gift.

His comment and my awkward response was a gift of enormous magnitude but it did not feel like a gift at the time. Yet, I am ever grateful he spoke up.


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Tags:  Featured  January-February 2013 

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Operating Portable Generators

Posted By Underwriters Laboratories, Tuesday, January 01, 2013
Updated: Thursday, December 13, 2012

When a hurricane downs power lines, electricity is often one of the initial services to fail. In response, many people use portable generators to weather the inconvenience until power is restored.

Carbon Monoxide Hazards

While a portable generator can solve some of the stress of managing a storm’s aftermath, consumers need to operate them with caution. Portable generators are powered by internal combustion engines. As the fuel burns to power the generator, it emits carbon monoxide (CO) into the air. If the generator isn’t properly positioned, consumers risk CO poisoning. "The danger of carbon monoxide poisoning from portable generators is a true threat during storm season,” says John Drengenberg, UL’s consumer affairs director. "But if you take the proper precautions, you can use a generator safely.”

UL, a global safety organization, recommends the following safety tips to protect against carbon monoxide poisoning:

Place the portable generator as far away from the home as possible –

• NEVER use a generator inside homes, garages, crawl spaces, or other partly enclosed areas. Deadly levels of carbon monoxide can build up in these areas. Using a fan or opening windows and doors does NOT supply enough fresh air.

• ONLY use a generator outside and far away from windows, doors, and vents. These openings can pull in generator exhaust.

Use a carbon monoxide alarm – Even when you use a generator correctly, CO may leak into the home. ALWAYS use a battery-powered or battery-backup CO alarm in the home.

• Follow instructions – Follow the instructions that are provided with your generator. Being mindful of these guidelines helps ensure that the CO produced by the generato will not find its way into the home, where it can potentially endanger occupants.


Electrical Hazards

NEVER power the house by connecting a generator to a receptacle outlet – The practice, known as "backfeeding,” is extremely dangerous and presents an electrocution risk. Generators used to power a building during an outage must be connected through transfer equipment that isolates the generator supply from the utility supply.

Use proper electrical connections – Use UL-listed outdoor extension cords when connecting the generator to run power back to the house. Also, note the maximum wattage a generator produces, and never exceed that amount with the appliances you plug in. Appliances should have their wattage listed on the products.

Ground fault circuit interrupters (GFCIs) – These can help prevent electrocution. The majority of portable generators do not include GFCI protection. Use of a portable GFCI is recommended. It requires no special knowledge or equipment to install. 

One type contains the GFCI circuitry in a self-contained enclosure with plug blades in the back and receptacle slots in the front. It can then be plugged into a receptacle, and the electrical products are plugged into the GFCI. Another type of portable GFCI is an extension cord combined with a GFCI. It adds flexibility in using receptacles that are not protected by GFCIs. Portable GFCIs should be used only on a temporary basis and should be tested prior to every use.

One type contains the GFCI circuitry in a self-contained enclosure with plug blades in the back and receptacle slots in the front. It can then be plugged into a receptacle, and the electrical products are plugged into the GFCI. Another type of portable GFCI is an extension cord combined with a GFCI. It adds flexibility in using receptacles that are not protected by GFCIs. Portable GFCIs should be used only on a temporary basis and should be tested prior to every use.

Portable generators typically are not weatherproof – They can pose the risk of electrocution and shock when used in wet conditions. Use them outdoors, but keep them protected from direct exposure to rain and water. Generators should be operated on a dry surface where water cannot reach them.

Generators vibrate in normal use – During and after use of the generator, inspect it as well as extension cords and power supply cords connected to it for damage resulting from vibration. Have damaged items repaired or replaced as necessary. Do not use plugs or cords that show signs of damage, such as broken or cracked insulation or damaged blades.


Fire Hazards

Limit gasoline storage and look for the UL Mark on gasoline containers – Gasoline expands when heated, producing fumes that can be ignited by the smallest spark. The more gas on hand, the more fumes in the air and the greater the risk of a fire starting from even a light switch or static electricity.

Fuel and vapors are extremely flammable – Before refueling the generator, shut the engine off and let it cool down, as fuel spilled on hot parts can ignite.

For more information, visit ul.com/hurricanesandy


© 2012 UL LLC All rights reserved. May not be copied or distributed without permission.

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Tags:  Featured  January-February 2013 

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401(k) Loans: The Last Resort?

Posted By Jesse Abercrombie, Tuesday, January 01, 2013
Updated: Friday, December 14, 2012

As you’re well aware, we’re living in difficult economic times. Consequently, you may be forced to make some financial moves you wouldn’t normally undertake. One such move you might be considering is taking out a loan from your 401(k) plan — but is this a good idea?

Of course, if you really need the money, and you have no alternatives, you may need to consider a 401(k) loan. Some employers allow 401(k) loans only in cases of financial hardship, although the definition of "hardship” can be flexible. But many employers allow these loans for just about any purpose. To learn the borrowing requirements for your particular plan, you’ll need to contact your plan administrator.

Generally, you can borrow up to $50,000, or one-half of your vested plan benefits, whichever is less. You’ve got up to five years to repay your loan, although the repayment period can be longer if you use the funds to buy a primary residence. And you pay yourself back with interest.  However, even though it’s easy to access your 401(k) through a loan, there are some valid reasons for avoiding this move, if at all possible. Here are a few to consider:

You might reduce your retirement savings. A 401(k) is designed to be a retirement savings vehicle. Your earnings potentially grow on a tax-deferred basis, so your money can accumulate faster than if it were placed in an investment on which you paid taxes every year. But if you take out a 401(k) loan, you’re removing valuable resources from your account — and even though you’re paying yourself back, you can never regain the time when your money could have been growing.

You might reduce your contributions. Once you start making loan payments, you might feel enough of a financial pinch that you feel forced to reduce the amount you contribute to your 401(k).

You may create a taxable situation.  Failure to pay back loans according to the specified terms can create a taxable distribution and possibly subject the distribution to a 10% penalty.

You may have to repay the loan quickly. As long as you continue working for the same employer, your repayment terms likely will not change. But if you leave your employment, either voluntarily or not, you’ll probably have to repay the loan in full within 60 days — and if you don’t, the remaining balance will be taxable. Plus, if you’re under age 59½, you’ll also have to pay a 10% penalty tax.

Considering these drawbacks to taking out a 401(k) loan, you may want to look elsewhere for money when you need it. But the best time to put away this money is well before you need it. Try to build an emergency fund containing at least six to 12 months’ worth of living expenses, and keep the money in a liquid vehicle. With this money, you’re primarily interested in protecting your principal, not in earning a high return.

A 401(k) is a great retirement savings vehicle. But a 401(k) loan? Not always a good idea. Do what you can to avoid it.


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Tags:  Featured  January-February 2013 

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2013 International President Steve Douglas — IAEI Focuses on 5 Goals for 2013

Posted By Steve Douglas, Tuesday, January 01, 2013
Updated: Friday, December 14, 2012

2013 International President Steve DouglasIncoming International President Steve Douglas has announced five goals for 2013. These undertakings are designed to assist IAEI in taking a giant step forward in membership, in the industry, in technology, in outreach and in establishing real presence in local communities and across the world.

First and foremost, IAEI is continually increasing value for its members. The implementation of a new website and moving towards electronic publications are some of the initiatives for accomplishing this goal.

IAEI codes and standards committee will continue to develop significant code proposals for future editions of both National Electrical Code and the Canadian Electrical Code. Through this process, IAEI members have a strong influence in the North American electrical safety system.

The capital campaign committee, under the leadership of Chuck Mello, will be ramping up its campaign to raise $2 million. Success in this project will ensure appropriate buildings, equipment and technology to allow IAEI to more forward and to be at the forefront of industry ventures.

A special committee has been established to review the international bylaws and operating rules in an effort to reduce duplications and to structure our bylaws in such a way that will allow our organization to be relevant in today’s industry. This fine tuning will enable the association to be more versatile and to respond to partnership and collaboration opportunities in a more timely fashion.

Considerable international interest in IAEI has developed through iaei.org and the social media. As a consequence, a new committee has been established to promote and to assist in the development of chapters and divisions internationally.  

Dave Clements, CEO, welcomes Steve and his background and expertise in electrical codes and standards; he feels confident that these will help Steve guide IAEI in achieving its goals.

About the president

President Steve Douglas joined IAEI in 1990 and attended his first Canadian Section meeting in 1991 in Kingston, Ontario. "At that time,” he recalls, "I did not understand the full impact IAEI has on the electrical safety infrastructure in North America. I was, however, very impressed with the technical program.”

 Photo 1. Stan Benton passes the presidency to Steve Douglas.

Photo 1. Stan Benton passes the presidency to Steve Douglas.

After six years, he was elected to the Ontario Chapter executive and was extremely active at the local level.  In 2001, he was elected to the International Board and has served eleven years, during which he has observed the board become more effective through the use of greater technology, such as web-based meetings, conference calls, and computerization.

 Photo 2. Anita and Steve Douglas

Photo 2. Anita and Steve Douglas

In 1996, Steve had the opportunity to represent IAEI on the Section 8 subcommittee of the Canadian Electrical Code Part I (CE Code). In 1998, IAEI member Roy Hicks, then chief electrical inspector for Ontario Hydro, was able to get an associate member position for IAEI on the CE Code. Steve was placed in this position and within six years was able to change the IAEI status from an associate member to a voting member on the CE Code. Within ten years, he was able to increase IAEI representation on the CE Code subcommittee from 6 subcommittees to all 43 subcommittees for the 2009 edition of the CE Code. IAEI is the first organization to have representation on all 43 sections of the CE Code since the first edition of the CE Code in 1927, and full section representation continued in the 2012 edition.

This Canadian achievement added to IAEI’s current representation in the U.S. on the National Electrical Code — the Technical Correlating Committee and all 19 code-making panels — gives IAEI and its members unique input into the electrical safety infrastructure in North America.

Presently, Steve is the vice chair of the CE Code Part I, chair of CE Code Part I Subcommittees for Section 2, 12, and 50, and a member on Sections 40, 64, 68, 76 and Appendix D. In addition, he is the chair of the CSA Standards C22.2 No. 273 Cablebus, C22.6 No. 1, Electrical Inspection Code for Existing Residential Occupancies committee, the chair of the SPE-1000 Working Group, and a member on committees for the Objective Based Industrial Electrical Code, Safety Management Systems, Solar Photovoltaic Modules, Photovoltaic Cable, Fuel Cells, Wind Turbines, Distribution Transformers, Outlet Boxes, and Wiring Fittings Hardware and Positioning Devices to name a few. In total, he is active on 53 technical codes and standards committees, which gives IAEI recognition on the CE Code and Standards.

Steve lives in Toronto, Ontario, with his wife of 29 years, Anita. They have two daughters. Lindsay and her husband Kevin are the parents of grandson Koen. Penny and Andrew are the parents of granddaughter, Savannah, and grandson, Landyn.

 Photo 3. Daughters Lindsay (left) and Penny (right) with grandchildren (left to right) Koen, Savannah and Landyn.

Photo 3. Daughters Lindsay (left) and Penny (right) with grandchildren (left to right) Koen, Savannah and Landyn.

Steve is currently the senior technical code specialist for QPS Evaluation Services Inc., a certification and field evaluation organization based out of Toronto.

"I am honored to be your international president for 2013, and I look forward to meeting more of you, members of the greatest association dedicated to electrical safety in the world — International Association of Electrical Inspectors,” Steve says.


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Tags:  Featured  January-February 2013 

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Cablebus

Posted By Steve Douglas, Tuesday, January 01, 2013
Updated: Friday, December 14, 2012

The new standard for cablebus C22.2 No 273 is scheduled for publication by September of this year. This new standard will be the first standard for cablebus in North America. The committee includes the six major cablebus manufacturers in North America, two switchgear manufacturers, CSA, and an IAEI representative. 

Cablebus is an assembly

Cablebus is an assembly of insulated conductors with fittings and conductor terminations in a completely enclosed, ventilated, or non-ventilated protective metal housing. In most cases, cablebus will be approved by either certification or field evaluation and is typically assembled at the point of installation from the components furnished by the cablebus manufacturer. Accompanying the cablebus, the manufacturer will provide installation instructions and drawings for the specific installation to facilitate:

a) system design;

b) construction;

c) fire stop rating (where applicable);

d) weatherproof entrance fittings (where appli-cable);

e) bonding, conductor and shield terminations (where applicable);

f) grounding of shields (where applicable) and installation;

g) inclusion of electrical detail of the conductor configuration, together with enclosure dimensions;

h) specification of maximum allowable span support; and

i) vertical installations.

Cablebus nameplate

To assist the electrical contractor and electrical inspector the main nameplate will include:

a)   The manufacturer’s name, trademark, or other descriptive marking by which the organization responsible for the product can be identified;

b)   The electrical ratings:

– rated nominal voltage, (Vrms or Vdc)

– frequency in Hz

– allowable ampacity  (Amps),  based on ambient temperature* of XX*C, and based on a maximum operating temperature of XX*C- short circuit current rating  

– number of phases (poles for dc);

– 3-wire or 4-wire; and

–Maximum continuous current rating _XX_A, when connected to a 100% continuous rated overcurrent device

– Maximum continuous current rating _XX_A, when connected to a 80% continuous rated overcurrent device

*Note: the temperature is the maximum ambient temperature that the equipment was designed to operate in.

c) The month and year of manufacture, at least, shall be marked on the cablebus system in a location accessible without the use of tools.

d)   The number of conductors and size per phase.

e) As a minimum, the allowable ampacity (amps) based on a maximum operating temperature of 75°C  shall be included on the nameplate.

f) Type of material, such as stainless steel (including the type), aluminum, etc., and, if carbon steel, Type 1 (hot-dip galvanized), Type 2 (mill galvanized), or Type 3 (electrodeposited zinc), as applicable. If the manufacturer’s catalogue number marked on the product would readily lead the user to the required information published by the manufacturer, this marking is not mandatory;

g) a warning label that reads, "WARNING! DO NOT USE AS A WALKWAY, LADDER, OR SUPPORT FOR PERSONNEL; and

h) the design drawing number for the specific installation.

Maximum continuous current rating

The maximum continuous current rating will assist in the application of CE Code Rules 12-2260 and 8-104 and help provide consistency with respect to conductor loading. In addition to these nameplate markings, cablebus will be one of two classes corresponding with the Items (a) and (b) in CE Code Rule 12-2252. CE Code Part I Rule 12-2252 states:

12-2252 Use of cablebus (see Appendix B)

Cablebus shall be permitted for use where

(a) protection from contact with conductors is provided by design and construction of the enclosure; or

(b) installation is intended in areas

(i) accessible only to authorized persons;

(ii) isolated by elevation or by barriers; and

(iii) where qualified electrical maintenance personnel service the installation.

Class A cablebus is designed with protection from conductors contact provided by the design and construction of the enclosure. Class B cablebus is intended to be installed in areas accessible to authorized persons, isolated by elevation or by barriers, and where qualified electrical maintenance personnel service the installation.


Steve Douglas is presently the senior technical codes specialist for QPS Evaluation Services. As the International Association of Electrical Inspectors representative on Part I and Part II of the Canadian Electrical Code, Steve is the vice chair of the CE Code Part I, chair of CE Code Part I Subcommittees for Section 2, 12, and 50, and a member on Sections 40, 64, 68, 76 and Appendix D. In addition, Steve is the chair of the CSA Standards C22.2 No. 273 Cablebus, C22.6 No. 1, Electrical Inspection Code for Existing Residential Occupancies committee; the chair of the SPE-1000 Working Group; and a member on committees for the Objective Based Industrial Electrical Code, Safety Management Systems, Solar Photovoltaic Modules, Photovoltaic Cable, Fuel Cells, Wind Turbines, Distribution transformers, Outlet Boxes, and Wiring Fittings Hardware and Positioning Devices. 

Tags:  Featured  January-February 2013 

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Article 240, Part 1 — Overcurrent Protection

Posted By Randy Hunter, Tuesday, January 01, 2013
Updated: Friday, December 14, 2012

Overcurrent protection is a subject on which we could write volumes; however, our objective here is to cover the basics in order to provide the information needed for the combination inspector. This is actually a fun portion of training, as we usually take apart devices and explore how they operate. Check out the included photos that illustrate some of the details that we usually look at in training classes, and don’t be hesitant about disassembling equipment (that you don’t plan to install later!) to see what is inside. 

To make sure we understand our topic, we need to start with the scope of this article. It provides the general requirements for overcurrent protection and overcurrent protective devices not more than 600 volts, nominal. There are two parts to Article 240 that we will not address: Part VIII dealing with supervised industrial installations and Part IX dealing with over 600 volts. Combination inspectors are generally not involved with these installations, so we will leave those topics to articles and books specifically concerned with those subjects.

 Photo 1. Overcurrent protection comes in many types, sizes and shapes

Photo 1. Overcurrent protection comes in many types, sizes and shapes

As with most NEC articles, we need to start with some unique definitions. Article 240 has only three definitions, and they are located in 240.2. First we have a definition of current-limiting overcurrent protective device, which is a device that when interrupting currents in its current-limiting range will reduce the current flowing downstream to a level much less than if there were just a solid conductor having comparable impedance. Current-limiting devices are very instrumental in reducing incident energy (arc flash, arc blast) in our electrical systems, making them safer for personnel and providing protection of equipment.

The second definition deals with a term that is also used in other parts of the code. Quite often we have a question as to what exactly is an "industrial installation”? In 240.2, we have a definition of supervised industrial installation with a list of conditions which must be met to fall under this definition. Note that this definition is specifically limited to use in Part VIII of Article 240; this means that these limitations do not apply to any other code provision where supervised industrial installation (or similar term) is used. You can’t use this definition when applying 392.10(B), for example, which allows certain cable tray wiring methods in industrial establishments. Since we are not covering Part VIII in depth, I simply point this out so that you know that this definition is very limited in application.

 Photo 2. Here is a very good example of a neutral main bonding jumper that was never properly connected after the completion of the ground fault testing. This caused several problems within this facility, including voltage fluctuations and equipment failures.

Photo 2. Here is a very good example of a neutral main bonding jumper that was never properly connected after the completion of the ground fault testing. This caused several problems within this facility, including voltage fluctuations and equipment failures.


The last definition is that of a tap conductor as used in this article. This definition is needed as we have various tap rules within Article 240 with very specific rules. Simply put, a tap conductor is a conductor other than a service conductor that has overcurrent protection ahead of it which is oversized compared to the normal requirements found in Article 240.

Basic minimum overcurrent protection

So, let’s get down to the most basic of rules for overcurrent protection. The go-to article here is 240.4. Other than flexible cords, flexible cables and fixture wire, we refer to the ampacities of the conductors as specified in Article 310.15, unless covered in specific applications as described in 240.4(A) through (G). In these subparagraphs, we cover basic minimum overcurrent protection device sizing according to conductor sizes and properties. These are very basic rules that will at times get overlooked when using ampacity tables, but you absolutely need to try to commit these to memory. Also, many code test questions will ask about sizing a certain type and size conductor, and you’ll get sidetracked into doing a calculation and don’t want to forget that you have limitations in 240.4. Please review these and remember some basic ones such as 14 AWG copper must have 15 amp protection, 12 AWG copper is limited to 20 amps and 10 AWG copper at 30 amps, just to name a few.

There are two very important rules in 240.4 that we have to examine more closely, as they deal with protection for 800 amps and lower and then over 800 amps. These general rules state that if you are sizing protection for 800 amps or lower, you are allowed to round up to the next largest device, as long as you don’t violate the specific conductors mentioned in 240.4(D). If you have a system over 800 amps, then the ampacity of the conductors has to equal or exceed the rating of the overcurrent device.

 Photo 3. This is a photo showing the interior of a 600-amp fuse after the sand filler has been removed.  This fuse opened during an overload condition.   You can see how five of the six alloy contact points melted and released; when the last one interrupted the flow of current, it arced and caused the burned sixth contact.  Please note in the left photo you can see the short-circuit elements which are still intact; these are the webs which melt out during a high fault current condition.

 Photo 3. This is a photo showing the interior of a 600-amp fuse after the sand filler has been removed.  This fuse opened during an overload condition.   You can see how five of the six alloy contact points melted and released; when the last one interrupted the flow of current, it arced and caused the burned sixth contact.  Please note in the left photo you can see the short-circuit elements which are still intact; these are the webs which melt out during a high fault current condition.


The next question that usually comes up here is: When allowed to round up to the next size device, what is the next size? The next size according to what is available from the manufacturer? No, you round up to the next standard size device according to 240.6. Please notice that in 240.5 you will find the specific overcurrent sizes for flexible cord, cables and fixture wire; again, the rules are very specific and in part mention exact size overcurrent protection according to the wire size. Please review, but know that generally speaking, we don’t see these wire types that often in combination inspections.

Standard ampere ratings

Let’s go back to Standard Ampere Ratings in 240.6. This is one section of your code book you will need to reference almost as often as conductor ampacities, so please remember it. Here you find what the code considers "standard sizes” when references are made to sizing overcurrent devices. I always make a big point of making sure everyone uses the sizes listed in this article when working on code questions or test questions. Another note here, remember when we had the rule that you round up when working at 800 amps and below? Well, you will notice the size differences below 800 amps are much closer, so when we round up it’s not much of a shift; however, when you get over 800 amps you will notice there are not as many options and the sizes start to jump in pretty large increments. This helps to explain the reasoning behind this code requirement, since rounding up in such large steps could lead to a large disparity between conductor ampacity and overcurrent protection levels.

Also in 240.6 are two paragraphs, (B) and (C), which work together to address adjustable trip circuit breakers. If you have an adjustable breaker which has the adjustment exposed with ready access, then the rating of that breaker will be the maximum possible setting. However, if these controls have a restricted access feature meeting the requirements as set forth in (C), then the rating of this device will be at the set value. The one gray area here is that some of the breakers have a field-fitted rating plug. It was my opinion as an inspector that if this plug type device could not be removed without the removal of sealable covers or special tooling of some sort, we applied 240.6(B). One such case had a plug which could easily be removed using a pair of needle nose pliers, so we opted for the conservative approach and applied (C).

 Photo 4. This photo shows the inside of a breaker. You can see some of the mechanical parts that are required for proper operation.

Photo 4. This photo shows the inside of a breaker. You can see some of the mechanical parts that are required for proper operation.


Fuses or circuit breakers in parallel

Questions appearing on some tests ask if it is permissible to use fuses and circuit breakers in parallel. This is addressed in 240.8. The correct answer is: only where they are a part of a factory assembly and listed as a unit. I have seen this from time to time, but never outside a factory listed unit.

Electrical system coordination

Continuing on, 240.12 starts us on the path for an interesting concept that often isn’t considered in design. The subject is electrical system coordination, and it simply states that to minimize hazard(s) to personnel and equipment where an orderly shutdown is required, a system of coordination based on two conditions shall be permitted. The first condition is coordinated short-circuit protection and the second is overload indication based a monitoring system or devices. Notice that this language says "shall be permitted.” This means that is allowed, but not required. This language is generally applied to situations where it is more hazardous to shut down the electrical source than it is to shut down the process. This is not the same as selective coordination, which is required for many emergency systems and will be covered when we finally get to Chapter 7.

Ground-fault protection of equipment

In 240.13 we find requirements for Ground-Fault Protection of Equipment. Let’s first consider the difference between ground-fault circuit interruption (GFCI) and ground-fault protection. The easiest way to explain this is that GFCI protection is for people and the threshold levels are extremely low (around 5 ma), whereas the protection of equipment is meant to minimize the damage to equipment in the event of a fault condition to ground. This applies to only a very specific power configuration and that is a solid wye-connected system, where the voltage to ground is more than 150 volts and the phase-to-phase voltage does not exceed 600 volts. Commonly this will be our 277/480 volts wye-connected three-phase systems that are 1000 amperes or more in size. Ground-fault protection offers a level of protection in the event of a ground fault at a much lower level of current than what the breaker is equipped to handle under normal operation. I’ll tell you a personal experience related to this. We had a bank in our jurisdiction where the service was rated at 1000 amps, 277/480 and so the inspector made a note that this installation would require ground-fault protection. The engineer stated it didn’t need it because he had specified an 800-amp main breaker. A little gray area I guess, but we decided to stick with the rating of the manufacturer’s label which stated the service equipment was 1000 amps. The end result was that the factory sent out new equipment labels and had a field inspection done by a listing agency to change the equipment to an 800-amp service officially.

Ground-fault protection needs a little deeper look, first to understand how it works and then to understand some of the complexities to look for as you are doing your inspections. First, these devices have a sensing ability to verify that the amount of current being called for is balanced and all accounted for between the other phases or the grounded conductor. In the event that we have current going to ground or not following the normal paths, then the ground-fault protection will open the device (this could be a breaker or a bolt switch equipped with the ground-fault protection). When these devices are sent out, they are set at factory minimums. If the levels are not adjusted at the time of installation, this minimum setting may cause nuisance tripping. The setting should be evaluated and specified by the engineer of record, and then set in the field to match the engineer’s design.

Once I got a service call for a large grocery store that had lost power. The main at this store had ground-fault protection, and the original contractor didn’t set up the device as requested by the engineer of record. So, it was still set at the minimum value. On the evening I got the call, the manager had asked a box boy to paint the hallway going upstairs to the break room, and the young man had saturated his roller to the point it caused some large drips to start running down the wall. The paint flowed into a 277-volt switch box and shorted out the switch. Well before the individual circuit breaker which fed the lighting circuit could interrupt the fault, the ground-fault device saw the fault to ground, did its job, and shut down the entire store. Because the device was not properly set by the installer, the entire facility lost power.

 Photo 5. This collage of photos shows a before-and-after for breakers.  The top row shows a breaker which has not been in operation.  The left and middle photos show both sides of the contacts, and the right photo shows the arc chutes.  The bottom row shows an example of the same parts of another breaker which has been subjected to a high fault current condition and had to open, causing damage to its components.

Photo 5. This collage of photos shows a before-and-after for breakers.  The top row shows a breaker which has not been in operation.  The left and middle photos show both sides of the contacts, and the right photo shows the arc chutes.  The bottom row shows an example of the same parts of another breaker which has been subjected to a high fault current condition and had to open, causing damage to its components.


Total separation of grounds and neutrals

Now one of the critical items we must look at during inspection is the total separation of grounds and neutrals downstream of the ground-fault device. This must be done all the way throughout the system down to each branch-circuit device and the equipment connected to the system. At the main service we have to pay special attention to have the grounds connected only to the grounding bar, and neutrals connected only to the neutral bar. Now this is different from our normal method, say in a residential main panel, where we can just mix the grounds and neutrals as we see fit. In these larger systems, there is a neutral bonding jumper (which could be a conductor but is generally a piece of busing) that comes from the factory and is not connected to the ground bar. As an inspector, you have to verify that the grounds terminate on the ground bar and the neutrals, to the neutral bar. If these are not done properly, the system will have issues.

Locally we always required third party verification and testing of the ground-fault system before we would approve it to be energized. This was our insurance that the unit had the grounds and neutrals separated throughout the entire facility and that the system wasn’t left at factory minimums. Once the system has been checked, then the neutral bonding jumper is connected between the neutral and the ground bar. So after we got this report, we would make sure the bonding jumper link was connected between the neutral and ground bar and then allow the contractor to have the system energized. This was our solution for enforcement of ground-fault protection of equipment.

In the next issue we will pick up with Part II of Article 240, but this is a good time to cover a related issue. While teaching classes on the code, I always tried to take the mystery out of the electrical system as much as possible. So I am going to spend a little time explaining how overcurrent and short-circuit protection works. In class this always led to a lot of show and tell, taking apart devices and physically seeing their operation. I will try to explain this here and supplement it with some good photos.

Basics of circuit protection

We need to explore some of the basics of circuit protection. First we’ll start with the most common circuit breaker in the industry today, that being an inverse time circuit breaker. These come in all sizes and ratings, from 15 amps and up. They are rated by amperage, voltage and interrupting rating. The first two items we should already be familiar with; however, the last is often overlooked. The interrupting rating is the amount of fault current the device is able to safely handle without catastrophic failure. Insuring the available fault current is less than the rating of the device is one of the inspection items we need to look for. Breakers are mechanical equipment; similar to any other mechanical device, they require a lot of pieces to work together with the proper timing to do their job. A car is a good comparison, as it is a mechanical device that has many pieces that have to operate in a certain sequence for proper operation. Also similar to cars, the need for exercise and maintenance for breakers should be considered. Inside a breaker we have two distinct methods which cause it to open, one being an overload which is normally up to about 6 times the handle rating, and the other being the short-circuit portion which reacts to shorts causing a high level of fault current to flow. The overload is normally handled by a bi-metallic element which when exposed to excessive current starts to heat up and it then deflects to contact the trip bar and release the trip mechanism. Breakers handle short circuits with a magnetic sensor which reacts to high current flow and opens a breaker as fast as it can. Remember these are mechanical, and as such they take a certain amount of time to react and then to complete the operation of shutting down the circuit. The photos illustrate the number of components inside a breaker and also show a close up of the contacts, the arc shields which control and manage the arcing when operating in high-fault conditions, and a bi-metallic strip.

The other most common method of circuit protection is fuses, which in many circles is considered old style due to the fact they’ve been used to protect electrical systems practically since the beginning. However, they still have a distinct use in today’s systems and provide some very unique methods of protection due partially to their simpler operation. The most commonly used fuse for construction is a dual element time-delay fuse. These have two distinct portions within each fuse; the first portion is a thermally reactive element which handles an overload situation. This element uses a melting alloy which has been specifically created for each size fuse. When it is exposed to an overload condition it will melt out and release, allowing the fuse to open. The short-circuit section of a  fuse consists of a web-style design which is designed to react to high-current flows and very rapidly melt out; as these melt and break away, the amount of metal mass left is diminished which limits the amount of current which can continue to pass through the fuse. Therefore, they are considered current-limiting by design. In order to control this arcing within the fuse, it is filled with sand. When the sand comes into contact with the extreme heat and arcing of the webs, it turns into glass to quench the arcing event and extinguish it.

I know the operation of a fuse sounds basic compared to a device full of mechanical components which have to work in unison, but that’s just how simple they are. Once a fuse opens, you replace them with a new fuse which restores the system back to its original level of protection. When a breaker has been subjected to fault current near its operating limit, it should be taken out of service and tested before using again. There are companies that test breakers to insure they operate in the proper time and current levels required and then re-certify them. If the breaker is not tested and re-certified, it may not protect the system during a future fault.

In the next issue we will continue with Article 240. Continue to review the code as these articles only cover the highlights you need to know.


Randy Hunter works for Cooper Bussmann.  He holds twelve inspections certifications from IAEI, ICC and IAPMO. Randy is IAEI Southwestern Section secretary, Southern Nevada IAEI Chapter president, a current member of CMP-17, voting member of UL 1563, Electric Spas, Equipment Assemblies, and Associated Equipment, and a former principal member of CMP-6. He has served on several Southern Nevada local code committees and electrical licensing committees. He has been a master electrician since 1988, and pri­or to that he designed and built computed numerically controlled (CNC) machine tools. 

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Behind the Meter Cover

Posted By Joseph Wages, Jr., Tuesday, January 01, 2013
Updated: Friday, December 14, 2012

Think you might know what lurks behind the meter cover? Chances are you will think twice after reading this article!

Electrical Metering Devices

Meter enclosures are part of every electrical system. But how often do you look inside the enclosure after it has been installed and energized? A utility provider provides electricity to a customer in order to make a profit. Typically, this is accomplished by metering the electrical system at the point of connection. Electronic receiver/transmitter (ERT) meters are becoming more of the norm in today’s electrical metering systems. They provide many benefits to the electric utility provider and to the customer. But, this could allow for many unforeseen problems as well.

Photo 1. A 400-ampere, single-phase meter enclosure located at the front entrance of a church and preschool. Men, women, and children visiting this location walk by this meter enclosure on a daily basis. What’s located behind the cover could prove deadly! And chances are it will not be discovered until there is a problem.

Photo 1. A 400-ampere, single-phase meter enclosure located at the front entrance of a church and preschool. Men, women, and children visiting this location walk by this meter enclosure on a daily basis. What’s located behind the cover could prove deadly! And chances are it will not be discovered until there is a problem.

The Good Ole Days and the Standard Electrical Meter

For many years the measurement of electricity went relatively unchanged. These metering devices worked adequately for the utility provider to accomplish the goal of registering electrical usage so that a utility bill could be generated. The customer received the monthly statement and would pay his or her bill.

In the event the customer fell in arrears and did not pay the monthly bills, a customer service representative would visit the location and disconnect the power. To accomplish this, the meter seal would be cut, the electric meter removed and booted off, and then reinserted into the meter base. The cover is then reinstalled and re-sealed until a time in which the customer pays the outstanding bill and any reconnection charges. In the event of tampering, the meter would either be removed and a blank inserted or the service conductors cut and disconnected at the weatherhead or utility pole.

Photo 2. Within the meter enclosure unknown to daily passersby are several potential dangers as can be seen, such as corrosion, effects of overheating to busbars and conductors, insulation failure as well as conductor damage.

Photo 2. Within the meter enclosure unknown to daily passersby are several potential dangers as can be seen, such as corrosion, effects of overheating to busbars and conductors, insulation failure as well as conductor damage.

When the service is ready to be reconnected, the customer service representative then returns to the property, cuts the meter seal, removes the meter, removes the boots and reinserts the meter. The cover is then installed and another seal applied. This returns electricity to the customer and usage is recorded for the next monthly billing cycle.

During this entire process there were several opportunities for the utility representative to notice and report any problems developing within the meter enclosure. Upon discovery, action could be taken to alleviate potential problems before they happened. Technology has changed the way that utilities gather billing information and even the disconnection of delinquent accounts. This has in turn made it even more imperative that electrical work within the meter enclosure be installed in a code-compliant fashion.

A statement must be mentioned concerning safety regarding this issue. Unbelievably, some customers take it upon themselves to reconnect their electricity without the approval of the serving utility. This has resulted in additional fees being accessed by utility and the electrical meter being removed or the conductors disconnected at the weatherhead or utility pole. This illegal activity can result in electrical accidents up to and including death. Qualified personnel are necessary to reconnect these services to assure the safety of the electrical system. Never attempt to reconnect your electrical service! Contact your friendly utility provider for help with this situation.

Photo 3. The interior of this meter enclosure depicts damage due to overheating and corrosion. Remember, none of this damage is visible from the outside of the meter enclosure.

Photo 3. The interior of this meter enclosure depicts damage due to overheating and corrosion. Remember, none of this damage is visible from the outside of the meter enclosure.


The ERT Meter

An electronic receiver/transmitter meter (ERT meter) is used in a network meter reading environment. It can be retrofitted into existing meter enclosures and is available in single- phase and three-phase models. The meter uses electronic modules to communicate power consumption and power quality to the utility provider. The meter also allows two-way communications from the utility provider to the customer. This allows the utility provider the opportunity to be aware of outages that occur and to respond much more quickly.

The use of ERT meters saves the utility provider from physically visiting the meter location on a monthly basis. The ERT meters have a low-powered radio device that permits them to be read from a distance. This allows meter readings to be collected electronically with a mobile data collector (usually a laptop computer) or with a handheld receiver. Technicians are able to download the readings for multiple meters at one time rather than walking from house to house to look at each individual meter.

In some cases, the utility can also disconnect and reconnect the customer remotely. This can be for nonpayment of their monthly bill or to head off high demand issues on the utility system. This can be handy during high usage periods where the provider needs to disconnect loads within structures to prevent brownouts or blackouts from affecting the system. Many household devices are being produced with communication features that communicate with the electronic meters. Utilities can disconnect AC units briefly to prevent issues on the system from occurring. Most generally the customer is unaware that this has even taken place. Some consumers have expressed concerns regarding this issue as it applies to privacy. Many customers enjoy the features of ERT meters. This technology allows the customer to monitor their electrical usage. This has also allowed the customer to change some of their usage patterns in order to save money on their electrical bills by using electricity in the off-peak periods.

As you can see, the use of this technology removes the "hands on, eyes in the field” that may have visited the enclosure and discovered a problem. This can result in minor situations arising that develop into major issues. These issues can be lessened by proper equipment installation and inspection.

Photo 4. Conductor damage due to insulation failure that is not detectable from the exterior of the meter enclosure.

Photo 4. Conductor damage due to insulation failure that is not detectable from the exterior of the meter enclosure.


Preventing These Problems Begins with You

The first line of defense in addressing this issue starts with the electrical contractor. The contractor must make sure that all material used for the installation is listed and labeled as per requirements found in NEC 110.3(B). Proper application of NEC requirements will help ensure a safe and compliant installation. NEC Article 110 covers the requirements for electrical installations. Requirements found within this article include working clearances, interrupting rating, mechanical execution of work, mounting and cooling of equipment, illumination, electrical connections, arc-flash, and field marking. There are other requirements that are useful and required throughout the NEC as well.

Care must be taken to follow the manufacturer’s installation instructions. Special care must be taken to use anti-oxidant compounds as required by the NEC and the manufacturer. These requirements are found in NEC 110.14. Conductors should be stripped and prepared properly so as to not damage the conductor. Specialized tools are necessary to assure that the specific torque requirements are followed for the lugs and conductors. Informative Annex I includes recommended tightening torque values to be used in the absence of the manufacturer’s recommended torque values. These values are taken from UL Standard 486A-B.

The next line of defense lies with the electrical inspector. The inspector needs to assure the customer and utility provider that the electrical contractor has followed the guidelines for properly installing the metering equipment. A good understanding of the NEC and any additional electrical requirements required by the utility provider are necessary. Some of these requirements have been previously discussed. Additionally, the inspector needs to make sure that proper grounding and bonding has been accomplished. Grounding and bonding requirements can be found in NEC Article 250. Also, remember that the insulated fitting required at NEC 300.4(G) is required due to conductor size, not conduit type. Bushings are required for various conduit types throughout the NEC such as at 344.46 for rigid metal conduit. There have been many instances where the electrical installation has been turned down by an inspector due to a missing conduit bushing or insulated fitting.

Photo 5. For years a standard 2s meter was adequate for the needs of the utility company. Today’s technological advances have spurred changes within the utility industry in order to compete and reduce operation costs. Electronic radio transmission (ERT) meters may be able to control some electrical devices within the structure through the electrical utility to prevent system problems. These include the refrigerator, the air conditioner or some other high usage item. Privacy issues have been expressed by some people.

Photo 5. For years a standard 2s meter was adequate for the needs of the utility company. Today’s technological advances have spurred changes within the utility industry in order to compete and reduce operation costs. Electronic radio transmission (ERT) meters may be able to control some electrical devices within the structure through the electrical utility to prevent system problems. These include the refrigerator, the air conditioner or some other high usage item. Privacy issues have been expressed by some people.


Arc Flash and Available Fault Current, a Deadly Combination

New to the 2011 NEC are 110.16 and 110.24 which deal with arc-flash and available fault current markings and requirements. Section 110.16 states that the marking shall be located so as to be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment. This includes meter socket enclosures as well as switchboards, panelboards, industrial control panels and other motor control centers. These requirements do not apply to dwelling units.

Service equipment must be marked with the maximum available fault current per NEC 110.24. This Code requirement further states that the field marking shall be legible and include the date that the fault-current calculation was performed. It must also be sufficiently durable to withstand the environment in which it has been installed. Modifications require that this calculation be verified and recalculated as necessary to ensure the service ratings are sufficient for the maximum available fault current at the line terminals of the equipment. An exception exists for industrial installations where conditions of maintenance and supervision ensure that only qualified persons service the equipment. Again, as previously stated these requirements do not apply to dwelling units.

These requirements help to ensure that whoever works on this equipment in the future is aware of the potential available fault current. This also brings up an interesting question. Who is responsible to adjust the modification markings to the existing equipment as per the requirements found within 110.24? Suppose the providing utility changes out the transformer to the building. Suppose the impedance is different from the existing transformer to the newly installed transformer. Who makes the changes to the marking at the service equipment? Is the building owner aware that these changes have been made and what effect it has on the available fault current to his equipment? Does the utility provider even know that this requirement is found within the NEC? How does this information get upgraded on the electrical equipment?

Photo 6. This electrical service location has a meter blank installed and the meter retired or taken out of service. This could be due to non-payment for services, tampering or because the electrical equipment is no longer in service.

Photo 6. This electrical service location has a meter blank installed and the meter retired or taken out of service. This could be due to non-payment for services, tampering or because the electrical equipment is no longer in service.


Most utilities work under the guidelines of the National Electrical Safety Code (NESC). During a power outage at 2:00 A.M. in the pouring rain and lightning, who will make these adjustments in the field? Is there communication between the utility provider and the customer concerning these changes? What happens when the utility changes the substation feeder to this area of town from one substation to another? There are different characteristics present in both substations that will affect the calculations towards what is marked on the service equipment. These are just a few questions and situations that could arise and affect the accuracy of the field markings for these installations.

Interestingly, during the 2011 NEC Report on Proposals (ROP) and Report on Comments (ROC) meetings these situations were vigorously debated and discussed. The inclusion of the date of when the calculation was conducted was agreed upon and included so that the future electrical contractor would be aware of when the calculation was conducted. Under no circumstances should the electrical contractor rely on a marking on the equipment to determine the level of personal protective equipment (PPE) required. Changes to the system may have taken place after the date the calculation was performed, changing the available fault current at the terminals of the equipment.

Technology Always Has its Ups and Downs

In conclusion, a properly installed and inspected electrical service should provide years of service to the customer. If the customer increases the electrical load by adding new electrical appliances, the service size may need to be re-evaluated. There are many existing older homes and commercial locations with electrical services that were acceptable at the time they were built. Over the years with the addition of new electrical appliances, these services may no longer be adequate for their situation. An electrical contractor should review these services and determine if modifications are needed.

Believe it or not, there are still several locations within utility territories that have only 120-volt services. Usually these are only 60-amp services. This service was all that was necessary to provide electricity to the few devices available at that time. Technology has brought us many new items to add comfort and convenience to our daily life. Many homeowners are shocked when they purchase a new air conditioner or electric dryer to find out that they will need to modify their electrical service to utilize the equipment. Many tend to be elderly and on a fixed income.

Field markings are crucial to the safety of the equipment, the electrician and the electrical inspector. All attempts should be made by the utility and the customer to maintain the accuracy of these markings. Doing so may mean the difference between life and death!

And remember to consult the utility provider and to secure the required permits from the authority having jurisdiction (AHJ) before beginning the electrical upgrade. The utility provider may need to re-evaluate transformer sizes and make adjustments to their system due to your planned modification. What worked for the utility years ago may need modification today.


Joseph Wages, Jr., is the education, codes and standards coordinator for IAEI. He represents IAEI as an alternate on NFPA CMP-3. He also serves on the UL Electrical Council and on several Technical Standard Panels. He is an ICC certified building official and holds certifications as building plans examiner, building inspector, chief building code analyst and one and two family dwelling inspector. He is also an IAEI certified electrical inspector for one- and two-family dwellings. Wages served on the State of Arkansas Apprenticeship Coordinating Steering Committee for four years. He was chief electrical inspector of Siloam Springs, Arkansas, for 15 years. He served as secretary/treasurer and education chairman for IAEI Arkansas Chapter since 2008 and as president for two years. He is a graduate of both the University of Arkansas/Fort Smith and the Northwest Technical Institute ACEF Apprenticeship Program. He has taught apprentices for the ACEF and classes for the Arkansas Chapter.

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Grain Elevator Safety

Posted By Thomas A. Domitrovich, Thursday, November 01, 2012
Updated: Tuesday, December 11, 2012

What’s tall, holds some dusty stuff, and at times can go boom? You guessed it, grain elevators. This just may be a topic you don’t hear discussed very often, yet there are statistics associated with these structures that may surprise you. Headlines such as "Three More Victims Found after Explosion at Kansas Grain Facility . . .” or "2 Hurt in Grain Elevator Explosion in Tracy, Minn. . .” are very concerning and found all too often. A simple Google search for "grain elevator explosion” brings to light the urgency of safety in these types of facilities. Grain elevators have been around for quite some time and will be around for years to come as they are critical not only to many farmers across this country but also to this country’s economy. The statistics and news reports tell us we need to be concerned about grain elevator safety, which deserves your attention and your efforts when it comes to preventing what is happening across the United States — explosions that claim millions of dollars in property and many lives.

Photo 1. Grain elevators enable the handling of loose grain in large volumes.

Photo 1. Grain elevators enable the handling of loose grain in large volumes.

Background

Grain elevators have been around for a very long time; they were invented in Buffalo in the 1842 /1843 time frame to eliminate the need to bag and handle grain. They enabled the handling of loose grain in large volumes. A grain elevator includes a complex of facilities focused on handling grain. That would include offices, weigh-bridges, storage facilities and more. The United States Department of Labor’s Occupational Safety & Health Administration (OSHA) describes grain handling facilities as those "that may receive, handle, store, process and ship bulk raw agricultural commodities such as (but not limited to) corn, wheat, oats, barley, sunflower seeds, and soybeans. Grain handling facilities include grain elevators, feed mills, flour mills, rice mills, dust pelletizing plants, dry corn mills, facilities with soybean flaking operations, and facilities with dry grinding operations of soycake” (http://www.osha.gov/SLTC/grainhandling/index.html). When it comes to safety concerns, any business that has a grain elevator on-site that is utilized for the storage, transport and/or processing of a raw agricultural commodity is a prime target. As an example, these may also include breweries where malt and other ingredients are stored.

These facilities usually employ a bucket elevator or a pneumatic conveyor to take grain from a lower level to a higher level ultimately deposited in a silo or other similar storage facility. They come in all shapes and sizes from smaller grain elevators found on a farm to large grain elevators run by companies that focus only on this aspect of the grain trade. These larger grain elevator complexes are the beginning of a journey for the grain they hold, which finds its way to grain wholesalers, exporters and local users, being emptied out of the silos or bins by gravity into railroad cars, barges or other movers like trucks. This is a very efficient way to handle massive amounts of grain and beats the backbreaking job of handling bags or sacks of the stuff. It’s a process that is critical to our U.S. economy.

The statistics around grain elevators and dust explosions, in general, command our attention. Over the ten-year period reported in table 1 coming out of a Kansas State University study, there were 16 deaths, 126 injuries and $162.8 million in damage due to "dust” explosions. Grain elevator explosions are specifically called out in this report showing 51 explosions over this ten-year period from 1996 through 2005. More recent statistics are available from OSHA and show that over a more recent ten-year period, 2001 through 2011, there have been 83 explosions 59 injuries and 13 deaths.

Table 1. U. S. Agricultural Dust Explosion Statistics

Table 1. U. S. Agricultural Dust Explosion Statistics

The above statistics cover explosions, but the hazards in these grain handling facilities are many. Having grown up in a steel mill town [Aliquippa] in the Pittsburgh, Pennsylvania, area, I can remember sitting around the table listening to my father talk about the dangers that he witnessed in the steel mill and the lives that were lost. Mills, grain elevators and similar types of facilities have certain things in common; there are high areas, gratings, many rotating machines and ultimately many locations where life and limb are at risk. Workers can be exposed to a wide variety of life-threatening hazards in these facilities. Some examples include, but are not limited to, fires and explosions from grain dust accumulation, suffocation from engulfment and entrapment in grain bins, falls from heights, crushing injuries and amputations from grain-handling equipment. Suffocation is the leading cause of death in grain bins. This typically occurs when a worker enters a filled bin and walks/works on the grain without fall protection. A person can be engulfed and trapped when caught in flowing grain. Bridged grain and vertical piles of stored grain can also engulf a worker who enters a bin. Contrary to what you may think, only a few seconds pass before you realize you are entrapped and engulfed by flowing grain, leaving you helpless to free yourself. Suffocation shortly follows as a result of being buried alive in the grain.

Table 2. Grain Elevator Explosions

Table 2. Grain Elevator Explosions

The bottom line is that the handling and transporting of grain creates many hazards in addition to the hazard of the dust created by the process. Unlike the other hazards, the dust problem is one that can become a ticking bomb. Dust is typically very fine and gets just about everywhere. This dust can become an important piece of the recipe for an explosion. The elements of a dust explosion include fuel, oxygen, containment/enclosure and an ignition source. The dust generated at these grain elevator environments is the fuel.

Dust as a Fuel

Any Boy Scout or Girl Scout can tell you how to start a fire — it doesn’t include grabbing the largest available log and holding a match to it. No, quite the opposite; you gather smaller materials (kindling) and ignite those first. In general, the hazard increases as particle sizes decrease. The surface area to mass ratio of the dust particle is a key criterion with combustible dust. The ability of a particular dust to explode is determined by its concentration in air and is influenced by factors such as chemical composition and particle size. In the January/February 2010 issue of IAEI magazine, the inaugural printing of the "Safety in Our States” column included a discussion specifically on how an electrical fire starts. The basic principles discussed there apply here as well. It was shared in that article that "When it comes to ignition, for a solid to burn, it must be volatilized. For ignition to occur, the material first must be capable of propagating self-sustained combustion. The warming, the heat, causes chemical bonds to break and the material to be decomposed into volatile substances which either ignites in the presence of a pilot or it auto ignites.” In that article, I focused on the burning of building materials; here we are talking about materials of much smaller size which increases the overall ignitible surface area. Dust particles, from a size perspective, are smaller than 0.42 mm (420 microns). For comparison sake, granules are in the 0.42 mm to 2 mm size and pellets are larger than 2 mm in diameter. The size of dust is important as there are code requirements that reference dust particle sizes. Article 500 of the NEC, Hazardous (Classified) Locations, Classes I, II, and III, Divisions 1 and 2, during the 2011 code cycle, introduced a definition for combustible dust as "Any finely divided solid material that is 420 microns (.017 in.) or smaller in diameter (material passing a U.S. No. 40 Standard Sieve) and presents a fire or explosion hazard when dispersed and ignited in air.” Proposal 14-9 of the 2011 cycle Report on Proposals (ROP), which is available at www.nfpa.org/70, was accepted to add this definition. This proposal was submitted by the American Chemistry Council (ACC) to retain the reference to dust size which was recently removed from other documents. This same definition made it into Article 506, as well.

Photo 2. The dust generated at these grain elevator environments is the fuel.

Photo 2. The dust generated at these grain elevator environments is the fuel.

Dust clouds present a very nice recipe for ignition as there is plenty of oxygen and surface area for ignition; but in addition to dust clouds, the presence of layered dust is also a significant safety concern. Dust can settle on horizontal and vertical surfaces, and to some extent, it can also settle on ceilings. This settled dust, depending upon the surface on which it has settled, has an opportunity to dry out, resulting in the lowering of its ignition temperature. This layered dust has been identified to be the source of damaging secondary explosions. Secondary explosions, in many cases, have been much more devastating than the initial explosion which may have resulted from ignition of airborne dust. It very well may have been a small explosion whose resulting pressure waves caused the structural vibrations that were enough to dislodge layered dust which, in turn, became fuel for yet another explosion. This secondary explosion will typically be much larger and result in a chain effect of more explosions, dislodging even more dust carrying the explosions well beyond an isolated location to quite possibly the entire facility.

Ignition Sources

I guess it would be accurate to say you can’t have an explosion without an ignition source. Ignition sources can come in different forms including thermal, mechanical or electrical energy. Welding, cutting operations, matches, lighters, cigarettes and even space heaters are all examples of ignition sources that have been identified in fire investigations as the cause of dust explosions. The source, though, doesn’t necessarily have to be some external activity to the process. The equipment itself can lead to ignition through friction, misaligned belts or pulleys, metallic buckets striking leg casings and slippage of belts and more; these are all sources of ignition. The point here is that you don’t need a flame to create a dust explosion. Over one-half of the dust explosions in Germany in 2005 were from non-flame sources. Common sources of ignition include:

  • electrostatic discharge
  • friction
  • arcing from machinery or other equipment
  • hot surfaces, including, e.g., overheated bearings
  • fire

It is, however, often difficult to determine the exact source of ignition post-explosion. Static charges can occur by friction at the surfaces of particles as they move against one another and build up to levels leading to a sudden discharge to earth. The use of electric power has also been identified. Sparks from the normal operation of switches, contacts, rotating machinery, and fuses can generate sufficient energy to ignite dust clouds. I have read of various incidents that involved electricity, including one where a light bulb with a faulty extension cord was being used to illuminate a bucket elevator boot pit and caused an explosion. The heat generated by arcing and sparking or even glowing contacts can generate the energy needed to ignite dust.

Photo 3. Sparks from the normal operation of switches, contacts, rotating machinery, and fuses can generate sufficient energy to ignite dust clouds.

Photo 3. Sparks from the normal operation of switches, contacts, rotating machinery, and fuses can generate sufficient energy to ignite dust clouds.

The recipe for disaster also includes the presence of oxygen and the containment/enclosure. The influence that oxygen has on fire is quite obvious and it is hard to reduce its presence. The amount of oxygen in air is more than adequate to support grain dust explosions. Falling or airborne dust acts to "mix” the dust particles with air. It is very desirable to minimize this mixing activity for obvious reasons. Combining an oxygen rich mixture of dust particles and a contained area with an ignition source provides the explosion with the right recipe for devastating energy.

The Safety Plan and Operating Procedures

I have two words when it comes to your safety plan — "Coin Up!” For those military personnel out there, you probably know what I’m talking about. Your safety plan is a critical part of your business and when challenged with the words "Coin Up” you should be able to produce it.

For those who may not be familiar, a challenge coin is something the military uses to enhance morale and remind Brothers in Arms of their commitment to each other. The origin of the challenge coin dates back to the Second World War where it was first used by the Office of Strategic Services personnel who were deployed in enemy held France. The coins back then were a local coin used to prove your identity. They were your bona fides that you had to produce during a meeting to help verify who you said you were. These coins may have been standard coins for the area, but they were unique in specific aspects such as the type, date, and a few other unique features of the coin. These details would be examined by each party, and they prevented infiltration into the meeting by spies. Today these coins represent each military individual’s commitment to his or her unit. Other organizations have produced these coins to raise awareness and to build bonds for many different reasons. The tradition of a challenge is the most common way to ensure that members are carrying the unit’s coin. The challenge begins when a challenger draws the coin and slaps it on the table or bar. Those being challenged must immediately produce their coins. Anyone failing to do so must buy a round of drinks for the challenger and for everyone else who has his or her challenge coin. However, if those being challenged produce their own coins, the challenger has to buy the round of drinks for the group. There are many different rules around the challenge but suffice it to say, for the purposes of this discussion, "Coin Up” is a challenge to produce your safety plan.

Photo 4. Combining an oxygen rich mixture of dust particles and a contained area with an ignition source provides the explosion with the right recipe for devastating energy.

Photo 4. Combining an oxygen rich mixture of dust particles and a contained area with an ignition source provides the explosion with the right recipe for devastating energy.

The following is by no means everything you need to include in your safety plan and procedures but are some highlights. Most of these were taken from NFPA 654, "Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids.” The referential documents offered as part of this article should be reviewed and understood and should ultimately influence the content of your safety plan and operating procedures.

Emergency Action Plan (EAP): Include your procedures for reporting of emergencies and evacuations. Include critical operations as well. Your employees need to understand how to assist in orderly evacuations. The EAP should be reviewed with all new hires, when their responsibilities change, and when the EAP changes. Include the EAP in your training. Make sure that you identify and follow applicable federal, state and local laws and regulations.

Grain Handling Requirements: You need at least two emergency escape routes from certain locations. Reference OSHA 1910.272(O)(1) and (2) for the requirements of these escape routes.

Safety Training: Make sure your training is job specific and some may say annually; but more frequent sessions are advisable. It’s important to ensure your employees can identify the hazard and understand how to prevent problems. Dust accumulation is a problem in these facilities. Ignition sources should be understood and identifiable. Those who have to access or enter bins must understand engulfment and mechanical hazards. Make sure they know their entry and rescue procedures.

Housekeeping: As discussed above, layered dust presents opportunities for subsequent explosions after the initial event. Your plans must include proper house cleaning which should call for the immediate cleaning when dust layers are noted to be 1/32-inch of thickness or more over a surface area of at least 5% of the floor area of the facility or the room. This thickness may change based on the type of dust as well. Make sure that there are no surfaces that are hard to get to and clean. Dust will continue to collect in these areas without your knowledge. Only use vacuum cleaners that are approved for dust collection.

Electrical Equipment: The use of appropriate electrical equipment for the environment and the proper wiring methods are very important to safety in these locations. Equipment bonding is very important. Some electrical equipment can become warm or hot. Motors, transformers, lights and other types of equipment not only offer surfaces for dust to rest but also act to dry that dust, again providing the perfect recipe for disaster.

Dust Control: In addition to housekeeping, there are ways to minimize the escape of dust from the process equipment. Ventilation systems should be considered as well as dust filters and collection systems. Minimize or eliminate activities that generate dust clouds, especially if ignition sources are present. As noted above, the ability to identify these dust cloud generating processes and ignition sources is critical.

Inspection: Inspect areas routinely. Make sure you have access to all areas and that there are no hidden surfaces that can accumulate dust.

Ignition Source Control: The ability to identify ignition sources should lead you to be able to limit these sources in your facility. Proper machine maintenance can help here as degrading machines may offer opportunities for friction and sparks to be generated. Heated surfaces and other sources of heat or sparks should be addressed.

Vehicles and Tools: The vehicles and tools on the job site should receive critical review. Maintenance of the vehicles, tools and equipment used in these dust areas is important to eliminate ignition sources and dust cloud generation.

Closing Remarks

Grain elevators are target rich environments when it comes to safety concerns. There are many tools available today to help ensure these facilities operate in a safe manner. We need to read, understand and "Coin Up” when it comes to our safety plans. Grain elevator explosions don’t have to occur. I hope this article stimulates the discussions that need to occur in various publications and educational forums to drive a downward trend in the statistics around grain elevator explosions.

Remember, keep safety at the top of your list and ensure you and those around you live to see another day.


Related Codes and Standards

 

Related NFPA Standards:

 

 

NFPA 61, Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities

 

 

NFPA 68, Guide for Venting of Deflagrations

 

 

NFPA 69, Standard on Explosion Prevention Systems

 

 

NFPA 70, National Electrical Code®

 

 

NFPA 91, Standard for Exhaust Systems for Air Conveying of Vapors, Gases, Mists, and Noncombustible Particulate Solids

 

 

NFPA 120, Standard for Fire Prevention and Control in Metal/Nonmetal Mining and Metal Mineral Processing Facilities

 

 

NFPA 432, Code for the Storage of Organic Peroxide Formulations

 

 

NFPA 480, Standard for the Storage, Handling, and Processing of Magnesium Solids and Powders

 

 

NFPA 481, Standard for the Production, Processing, Handling, and Storage of Titanium

 

 

NFPA 482, Standard for the Production, Processing, Handling, and Storage of Zirconium

 

 

NFPA 484, Standard for Combustible Metals, Metal Powders, and Metal Dusts

 

 

NFPA 485, Standard for the Storage, Handling, Processing, and Use of Lithium Metal

 

 

NFPA 495, Explosive Materials Code

 

 

NFPA 499, Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas

 

 

NFPA 505, Fire Safety Standard for Powered Industrial Trucks Including Type Designations, Areas of Use, Conversions, Maintenance, and Operation

 

 

NFPA 560, Standard for the Storage, Handling, and Use of Ethylene Oxide for Sterilization and Fumigation

 

 

NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids

 

 

NFPA 655, Standard for Prevention of Sulfur Fires and Explosions

 

 

NFPA 664, Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities

 

 

NFPA 1124, Code for the Manufacture, Transportation, Storage, and Retail Sales of Fireworks and Pyrotechnic Articles

 

 

NFPA 1125, Code for the Manufacture of Model Rocket and High Power Rocket Motors

 

 


Related ASTM Standards:

 

 

E789-95 Standard Test Method for Dust Explosions in a 1.2-Litre Closed Cylindrical Vessel

 

 

E1226-00e1 Standard Test Method for Pressure and Rate of Pressure Rise for Combustible Dusts

 

 

E1491-97 Standard Test Method for Minimum Autoignition Temperature of Dust Clouds

 

 

E1515-03a Standard Test Method for Minimum Explosible Concentration of Combustible Dusts

 

 

E2021-01 Standard Test Method for Hot- Surface Ignition Temperature of Dust Layers

 

 


Related OSHA standards found in 29 CFR:

 

 

1910.22 - General Requirements: Housekeeping

 

 

1910.38 - Emergency Action Plans

 

 

1910.94 - Ventilation

 

 

1910.107 - Spray Finishing Using Flammable and Combustible Materials

 

 

1910.146 - Permit-Required Confined Spaces (references combustible dust)

 

 

1910.178 - Powered Industrial Trucks

 

 

1910.269 - Electrical Power Generation, Transmission and Distribution (coal handling)

 

 

1910.272 - Grain Handling Facilities

 

 

1910.307 - Hazardous (classified) Locations (for electrical equipment)

 

 

1910.1200 - Hazard Communication

 


Read more by Thomas A. Domitrovich

Tags:  Featured  November-December 2012 

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Article 230, Services

Posted By Randy Hunter, Thursday, November 01, 2012
Updated: Tuesday, December 11, 2012

Article 230 is in some ways the genesis of the electrical system, meaning that it is very often the starting point of the electrical installation for a facility. Therefore, this is where I would usually commence my inspection process. As a rule of thumb, if the service is installed in a good workmanlike manner, the rest of the installation would also look good. However, if the service is a mess, you can generally assume that you are in for a long inspection and several items to note on your inspection record. The service is the location where we have some very specific things that have to happen to insure a good reliable system for the rest of the installation. The scope of this article covers the service conductors and equipment for control and protection of services and their installation requirements.

If we do a little review, the first item to remember is the term service point. Generally, it will be very close to the location of the service; and for most residential installations which are fed underground, the service point is at the meter base (see photo 1). From the service point, we start what we call the "service” which may consist of underground or overheard conductors, and then we will actually reach what most refer to as the service, or the main disconnect. If you will look at the first page of Article 230, you will find one of those handy road maps for the NEC. This diagram is a quick reference as to where you will find the requirements for a service installation.

Photo 1. This photo shows the service point, which is at the conductor terminations below the meter.

 

Photo 1. This photo shows the service point, which is at the conductor terminations below the meter.

 

In 230.2 we find the limitation on the number of services for a building or structure; one service is usually all that is required. However, we may have special conditions which would qualify for an additional service. These are commonly at larger locations which will have fire pumps, emergency systems fed from generators, and now with the sudden rise in alternative energy, we may find other types of services (see photo 3). In 230.2(B), Special Occupancies, we have language which allows multiple services for larger facilities. Often on larger apartment complexes, you may find more than one service. This is commonly true if the serving utility supplies a single-phase service which can be limited in capacity. For example, we are limited to only 600 amps for this type of service by the utility in my area. We’ve even had large custom homes which had more than one service due to this limitation. This condition is covered in (C), and again you should be getting used to the fact that one set of rules doesn’t fit every condition, so we add the last sentence to (C) which is "by special permission.” This means that the AHJ can grant permission depending on justification which he sees fit to accept. An example of this would be some of the newer data centers being constructed where reliability is of the upmost importance, requiring redundancy within the system.

Continuing with 230.2 in (D), Different Characteristics, you will find that if you have the need for different voltages you may be allowed to have an additional service. This is common in a manufacturing facility where the office may be supplied for a 120/208-volt, 3-phase service; however, the plant has larger equipment which is more efficiently run on a 277/480-volt, 3-phase system. The last part of 230.2 is the Identification requirement, which states that if a location has more than one service or a combination of sources, then we will have to properly inform people of the other locations of power feeding that location. This is accomplished by the use of a permanent plaque or directory installed at each service notifying one of all the other service, feeders and branch circuits supplying the building or structure. As I mentioned in the last article, this is the same requirement as found in 225.37. This is more than just a convenience for the electrician, it is also for our first responders who in the event of an emergency need to disconnect all power sources to a facility and to do so in a fast, orderly fashion.

Photo 2. Here is an example of a large service with signage to identify the main. As a local amendment, Las Vegas codes require the main to have a yellow sign, which helps the first responders identify the mains service disconnects.

Photo 2. Here is an example of a large service with signage to identify the main. As a local amendment, Las Vegas codes require the main to have a yellow sign, which helps the first responders identify the mains service disconnects.

Briefly I will mention 230.3, which states that service conductors may not pass through the interior of another building. This leads us right into 230.6 which outlines what is considered to be outside of a building. Here you will find that if conductors are beneath a building under 2″ of concrete or buried 18″ down, or if you have a raceway totally encased in 2″ of concrete within a building, these conditions would be considered outside. In the 2011 edition of the NEC, we now have a new addition to this section, which is that a service riser conduit may pass through an eave when installed on the outside of a building. This is one of those areas I had never considered as inside a building for the short distance that the riser may pass through an eave; however, I guess technically it was.

The next two sections mention that no other conductors shall be contained within a raceway or cable with service conductors, with only two exceptions (which I will trust you to review, as these conditions don’t happen often). However, the requirement for raceway seals in 230.8 is one of the most overlooked and missed inspection items I’ve seen, even though it can have catastrophic results if not followed. Simply put, if you have raceways entering from underground you are to seal them, even spare empty conduits. There are several products on the market which are great for this, even duct seal putty or clay will do the job just fine. One of the reasons for this requirement is that if you have some condition which will cause overheating of the underground conductors and they are installed in PVC conduit, the conduit might exceed its allowable temperature and start to degrade and even off-gas. These gases could be and often are very flammable; so if there is any type of an ignition source, like a loose connection or an arc from a breaker actuation, it may cause these gasses to explode. This makes for great photos, however, it is very expensive to repair and the lost time for this type of failure is huge. The simple task of sealing these with an approved method limits this type of condition and could save thousands of dollars.

We will now cover several items which were mentioned briefly in my previous article. I stated in the last edition that there is a huge overlap between Articles 225 and 230 when it comes to clearances, so this will be a bit of review. However, don’t discount the importance of these requirements, as they are all related to safe installations. So open the code book and please review the actual language as I summarize these again. First in 230.9 and 230.10, we find that we need to keep conductors 3 ft. from any openings, which will include windows, doors, porches, balconies, ladders, stairs, fire escapes or similar locations.

Photo 3. Here is an example of multiple services to one building, the normal power on the right and the alternate energy service on the left.

Photo 3. Here is an example of multiple services to one building, the normal power on the right and the alternate energy service on the left.

Overhead service conductors shall not be installed beneath any openings through which materials may be moved — which would include farm or other locations which may load and unload at an elevated portal — nor shall they block any building openings. And again vegetation shall not be used as a supporting means. Which brings to mind a situation, if you have a lodge pole pine tree that has died, is this still considered vegetation or is it now considered a utility pole? Where is the AHJ when you need him?

In Part II of 230 we get into specifics for overhead service conductors. First, these conductors are to be insulated, with one exception: the grounded conductor may not need to be insulated if it is part of a cable assembly. Next, we find the size and rating requirements. Generally, the conductors are to be sized to carry the calculated load as covered in Article 220; however, we do have a minimum size requirement in 230.23(B) which is 8 AWG copper or 6 AWG aluminum conductors. In 230.24 (A) and (B), we get into the specific clearances for overhead conductors which state they shall not be readily accessible, and it then expands further to explain what makes them meet this requirement. First, they shall have an 8-ft clearance over roofs, with five exceptions. Please read and review these on your own.

Next, we get the clearances from final grade. If the service voltage doesn’t exceed 150 volts to ground and the area is only accessible to pedestrians, then we only need a 10-ft clearance. This would commonly be a backyard. Next we cover residential property and driveways, and those commercial areas not subject to truck traffic, where the voltage doesn’t exceed 300 volts to ground. Here we need 12 feet of clearance, unless the voltage exceeds the 300-volt threshold, then the distance moves up to 15 feet.

Now for the last clearance: public streets, roads, and parking areas. Here we must have an 18-ft clearance. This is very important, as I’ve seen services pulled off walls by tall vehicles as a result of overhead conductors not meeting this requirement. This can obviously be a very dangerous condition. Also, please keep in mind that at certain times of the year we may have additional cable sag, which isn’t covered in the code specifically, but should be a design consideration.

One of the most important items to remember when in this area for those doing residential inspections is the additional clearance needed when dealing with swimming pools. This has to be mentioned here and you should take a moment to go to Article 680.8 and make sure you are aware of these distances, so that if you see a pool the little bell goes off in your head that you should double check all those clearance requirements specifically related to pools. Also note that in the 2011 NEC, we have new language to consider in 230.24(E) which mentions the clearance requirements from communication wires and cables.

Articles 230.26 through 230.28 deal with the attachment and support of overhead service conductors. The point of attachment shall never be lower than 10 feet, they shall be attached using fittings identified for the use with service conductors, and if the service mast is used as the support of the final span of the service conductors, it shall be of adequate strength. I mentioned in the last issue what I considered adequate. All this language boils down to this type of an installation, where the conductors are secured by a wedge clamp device that grips the bare grounded conductor which also has the steel core strand for strength, and then the conductors enter the raceway system through a weatherhead fitting.

Next we need to jump briefly to underground service conductors. These are generally utility-owned up to the meter, but you may have different local conditions. Underground service conductors are required to be insulated for the applied voltage, again with a few exceptions, which I will leave for you to review. The size and rating of these conductors don’t vary much from the overhead conditions. Where we have a different situation, in 230.32, Protection Against Damage, please note that the main reference here is to 300.5, where you will find a fair amount of installation requirements, do and don’ts, which we will cover when we reach that portion of the code. And the last item for underground service conductors is 230.33, which deals with splices. In rare cases, we may have to do splices, and this will refer you to the proper code requirements which may fit your application.

Photo 4. As an AHJ we are called out for all kinds of things. Here we had to investigate why a customer still had power even though he had no meter. However, getting past that issue, this photo is a good example of a weatherhead fitting for the proper conductor entrance to the raceway system, including a wedge clamp device which secures the conductors to the riser conduit.

Photo 4. As an AHJ we are called out for all kinds of things. Here we had to investigate why a customer still had power even though he had no meter. However, getting past that issue, this photo is a good example of a weatherhead fitting for the proper conductor entrance to the raceway system, including a wedge clamp device which secures the conductors to the riser conduit.

We now move on to Section IV of Article 230, which is titled Service-Entrance Conductors, so this would appear to cover both the underground and the overhead applications. Section 230.40 states that each service drop, overhead service conductors, underground service conductors or service lateral shall only serve one set of service-entrance conductors. A little review here: remember the difference between overhead and underground service conductors and the overhead drop and the service lateral is dependent on who owns that portion of the system. The ironic part of 230.40 is that we follow it up with nearly half a page of exceptions to this simple one sentence requirement. One of these exceptions will allow multiple service-entrance conductors if we have multiple occupancies. From my experience, when you have a condition which isn’t simply a one-on-one situation, I would recommend reviewing this section of the code carefully to see which condition best matches what you are seeing in the field and work from there.

Moving on, I want to jump up to 230.44. I mention this only to introduce you to the fact that a cable tray installation is permitted for service-entrance conductors.

Let’s move on to more of the mechanics of service installations. In 230.54, we actually begin with the requirements for service heads where the conductors enter a raceway system. Here we cover some simple but very essential items related to how to make sure we have a good weatherproof installation and points of attachment, so we do everything possible to prevent moisture infiltration into our equipment (see photo 4). This would include a drip loop, which is one of the most basic items which I see being done poorly. The intent of a drip loop is to provide a path for water that comes in contact with the wire to drip off of a low point without directing the water into the raceway or into the connections.

So we have danced all around services, but the most basic item in a service we haven’t touched yet, and we finally get to it in Section V, Service Equipment – Disconnecting Means. Now comes the basic items that we typically train combination inspectors to concentrate on when doing service inspections, many of which are service change-outs or upgrades (see photos 5 and 6). The first item is that a means shall be provided to disconnect all conductors in a building or structure from the service-entrance conductors. In 230.70(A) we explore locations for these disconnects. The main rule is that they shall be in a readily accessible location, followed by an item stating that they shall not be in a bathroom. This leads to a little humor as bathrooms are a location I would not consider to be always readily accessible anyway. However, as we’ve said before, much of the code is written due to various interpretations which have caused the need for clarification. The next obvious but frequently missed item is that all service disconnecting means must be suitable for the prevailing conditions; this may require a certain rating of the equipment, or protection.

We continue into 230.71, where we are given the maximum number of disconnects for each set of service-entrance conductors. You will notice that I stated this in a particular way, as I’ve had enforcement issues before where we have tried to state that you are only allowed a maximum of six switches per building for disconnecting means; however, the code doesn’t exactly state that. If you have multiple sets of service-entrance conductors, you can have up to six for each set. Also we have a list of additional items which may be in your service equipment but are not included in this requirement, such as power monitoring equipment, surge-protective devices and a couple of other items.

Grouping of the Disconnects, 230.72, covers the requirement to have disconnects grouped. One of the most important items is that each disconnect shall be marked to indicate the load served: this is a must (see photo 2). The allowance for additional disconnects for such things as fire pumps, emergency systems and such are allowed above the six disconnect rule, but the code wants these separated from the others. The exact words are that these shall be "remote” from the others, so this is an AHJ call as to what is "remote.” One of the other issues that I’ve seen in multi-occupancy businesses is the fact that each occupant shall have access to the service disconnection means. This can be a real issue when the electrical rooms are often locked and the owners don’t like to give every tenant keys to the room. One reason for restricted access is to prevent tenants from storing stuff in the electrical room. Remember, we must maintain proper working clearances, and storage and electrical rooms don’t go together. One of the worst I discovered was a shopping center that decided they needed a security staff. Of course, they had to have an office to work out of, so they made the electrical room into a security office, complete with desks, chairs, microwave, lockers and more.

Electrical rooms that have service disconnects in them have to be maintained and have to allow easy access so that in the event of something getting out of hand, or the need arises to shut down a unit, it can be done without delay or creating a hazardous condition.

Photo 5 and 6. These photos show why we are writing these articles, because as combination inspectors we are running onto these types of code violation installations daily.

Photo 5 and 6. These photos show why we are writing these articles, because as combination inspectors we are running onto these types of code violation installations daily.

This leads to another issue we need to mention here; often these electrical rooms may be very large and the location of the multiple main disconnects may not always be obvious. It could even be on the backside of the equipment you see when you first enter the room. In these cases, we need to provide some form of information as to where each disconnect is. Remember, we could be dealing with first responders who are not familiar with all forms of electrical equipment, so proper signage and whatever else can be done to direct them to each main disconnect will be helpful.

Locally, one option was to paint yellow lines on the floor to guide firefighters to each switch location. We have to keep in mind that personnel may face conditions that are not optimal, such as impaired visibility due to smoke, so the markings on the floor may give us the most advantageous condition. Along with this thought, 230.77 states that it shall be plainly indicated if the switch is in the open (off) or closed (on) position.

Moving along, we have to review the rating of disconnects. Here we find some minimum sizes for certain types of services. First, it must be sized according to the load calculated back in Article 220. Now for some special conditions, if you have a one-circuit installation, then the minimum service shall not be smaller than 15 amps, as detailed in 230.79(A). In (B), a two-circuit service is limited to 30 amps. Moving up to a one-family dwelling in (C), the minimum is 100 amps, 3-wire. And then for the all others, there is a catchall in (D) where the smallest service shall be 60 amps.

Section VII, Service Equipment – Overcurrent Protection, starts with a very basic requirement: each ungrounded conductor shall have overcurrent protection. Further, the rating of this overcurrent device shall not exceed the rating of the conductor ampacity. However, no overcurrent device shall be installed in the grounded conductor, unless the breaker is one that simultaneously disconnects the grounded and the ungrounded conductors. The service overcurrent device shall be an integral part of the service disconnecting means or shall be located immediately adjacent thereto.

The last thing we need to review in this article is 230.95, Ground-Fault Protection of Equipment. There are a few conditions that have to be met to kick in this requirement. First, the service has to be rated 1000 amps or more, and be a solidly grounded wye service of more than 150 volts to ground but not exceeding 600 volts phase-to-phase. So what fits this? It would commonly be our 277/480 wye services. The grounded conductor shall be solidly connected to ground through a grounding electrode conductor. The other information related to this requirement covers the settings, fuses, and the performance testing requirement. Generally speaking, on the ground fault protected systems we had in our area, we required third party testing. This would insure that the devices were set at the proper settings according the installation and the design professional’s requirements. From the factory, the settings are generally set to minimums which will cause nuisance tripping if not adjusted properly. We would then get a copy of this report and submit it as part of the record for the job. This was the best way, due to the time and equipment required, for this type of testing to be conducted. One extra note here, as simple as this may sound it is always a good idea to have this done and the report in hand before you authorize it to be energized.

This concludes Article 230; once again we have only hit the high spots and provided information which is common in the field and for testing purposes. Please take the time to thoroughly review the article in detail for those areas not specifically covered here. In the next issue, we will cover Article 240, Overcurrent Protection.


Read more by Randy Hunter

Tags:  Featured  November-December 2012 

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