Print Page   |   Contact Us   |   Sign In   |   Join
IAEI Magazine
Blog Home All Blogs
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.

Issue Archive | Advertise | Media Kit | Submit Article


Search all posts for:   


Top tags: Featured  UL Question Corner  Canadian Code  Editorial  Other Code  Canadian Perspective  May-June 2012  November-December 2011  Safety in Our States  January-February 2012  March-April 2012  January-February 2008  September-October 2012  July-August 2011  May-June 2005  May-June 2010  May-June 2011  November-December 2000  November-December 2010  January-February 2009  July-August 2006  March-April 2005  March-April 2011  May-June 2003  November-December 2008  November-December 2012  January-February 2010  July-August 2009  November-December 2009  September-October 2005 

Utility Deregulation, What Does it Mean to Inspectors?

Posted By Len Frier, Tuesday, May 01, 2007
Updated: Sunday, February 10, 2013

Deregulation of electric utilities is sweeping the country and is now available almost everywhere. The theory is that competition in the purchase of electric power would result in cheaper electricity and make utilities more responsive to consumers. This may be good in some areas and bad in others but it does put certain new elements of an electrical system under the authority of the local jurisdiction.

Utilities have historically been exempted from requirements in the National Electrical Code. They controlled all of their system up to and including the watthour meter in a facility. Electrical inspectors inspected from the meter into the facility. That is no longer the case. It is now possible for an owner to own the electric meters and all of the wiring from the main service drop. It is attractive for landlords of large apartment projects or other multiple occupancy facilities to buy their electricity wholesale and sell it to each tenant retail. Additionally, a tenant is less likely to leave the air-conditioning or heat on unnecessarily when they are paying for its usage.

Often, there is no control or requirements on these meters. Local public utility commissions may have requirements on the accuracy of a meter but usually not on safety. What’s more is that these meters can be lethal since they are usually connected to unfused wiring. Circuit protection is usually on the load side of a meter with no protection of the meter itself. A short circuit in the meter may only be isolated by the primary protection of a transformer or a circuit protective device feeding multiple meters. When inspecting a system an electrical inspector is usually not accustomed to looking at the meter. Additionally, there may not be a clear indication as to whether it is a utility meter or a customer-owned meter. Considering that there are watthour meters on the market that cost less that $10.00 each, the potential for a very dangerous condition exists.

Wiring and devices within a facility are usually properly protected yet in order to assure safety are still required to be labeled by a nationally recognized testing laboratory (NRTL). However, a watthour meter located prior to any overcurrent protective device in the building presents a major hazard in an installation. These meters have to withstand short-circuit currents from shorts in a building and surge voltages from outside the building. In addition, sever stresses should not cause the meter elements to burn open, preventing the meter from accurately registering the power consumption. The standards to which these meters are tested take all of these possibilities into account and result in a meter that is both safe and accurate.

To be safe, watthour meters not owned by the utility should be listed and labeled by a nationally recognized testing laboratory (NRTL) just as any other electrical device in a facility. To provide further assurance of quality, accuracy and dependability, the meter should also be certified to comply with the ANSI C12 compilation of standards. These standards assure accuracy and functionality in outdoor (wet, cold, hot and humid) environments. Safety determined by UL Standard 61010-1 does not necessarily include all of the environmental conditions a meter can be subjected to. Therefore the safety testing must include many of the ANSI C12 requirements. Although, performance and accuracy are not necessarily under the jurisdiction of the authority having jurisdiction, it would be serving the public well to know that the metering is accurate, dependable in addition to safe.

Read more by Len Frier

Tags:  Featured  May-June 2007 

Share |
PermalinkComments (0)

The Texas Margin Tax: There’s a New Tariff in Town

Posted By Jay D. Crutcher, Esq., Tuesday, May 01, 2007
Updated: Sunday, February 10, 2013

For two and half years in IAEI News, Jesse Abercrombie has been addressing financial issues of concern to those in the electrical industry. For this issue, he has submitted a guest article by Attorney Jay Crutcher, who will discuss a new tax in Texas. It is not yet known whether other states are implementing similar taxes. —The Editor

There’s a new tariff in town called the Texas Margin Tax. The margin tax replaces the old franchise tax and affects virtually every business entity in Texas (including out-of-state companies "doing business” in Texas). Vast numbers of limited partnerships, previously exempt from the old franchise tax, will now pay margin tax and it could be a sizeable amount. Corporations and limited liability companies that paid the old franchise tax will calculate margin tax using methods significantly different from the old franchise tax. Businesses now face new reporting rules for combined groups and tiered-partnership arrangements. In short, the margin tax affects business owners in fundamental ways — how they structure (or restructure) their businesses, how they account for their business operations, how they file their margin tax returns, and bottom-line, how much tax they pay. As a business owner, you need to know exactly how the margin tax affects your business so that you can take proactive measures to minimize your tax liability. Otherwise, you could face a surprising tax bill or overlook tax planning opportunities. This article describes who pays the margin tax and how much they pay.

Taxable Entities

The margin tax applies to a taxable entity. Most business entities, including limited partnerships, are considered to be a taxable entity. Limited partnerships were exempt from the old franchise tax. Prior to the margin tax, many businesses operated as a limited partnership to avoid franchise tax liability. One of the primary legislative purposes behind the margin tax was to eliminate the old franchise tax exemption for the vast majority of limited partnerships.

Passive Entities

The margin tax does not apply to a passive entity. To qualify as a passive entity, the business must be organized as a general partnership, limited partnership or non-business trust. A limited liability company does not qualify as a passive entity. Also, the business must satisfy specific passive income tests prescribed by the margin tax statute. Oddly enough, the margin tax statute expressly provides that rent is not passive income.

Margin Math: Taxable Margin

The margin tax rate is 1% for most businesses. Some businesses qualify for a lower rate of 0.5%. A business pays margin tax based upon its taxable margin. The business calculates taxable margin using one of three methods: (1) the cost of goods sold method, (2) the compensation method, or (3) the 70% percent method. The business uses the method that results in the lowest taxable margin. The business can elect to use a different method from year to year and is not required to use the same method each year. The old franchise tax was based on a net income concept. By changing the tax base to a gross margin concept, the margin tax potentially disregards many deductions.

Taxable Margin: The Texas Six-Step

A business calculates its taxable margin in basically six steps:

  1. First, the business determines its total revenue. Revenue exclusions apply for certain types of revenue. Special rules apply to specific types of businesses, including construction companies and contractors;
  2. Second, the business determines its cost of goods sold. The margin tax statute enumerates eligible costs and excluded costs. Special rules apply to construction companies, projects involving real property, and companies that lease heavy construction equipment;
  3. Third, the business determines its compensation. Compensation includes W-2 wages and, in certain cases, distributive shares of income from partnerships, limited liability companies and "S” corporations. However, the compensation deduction is limited to $300,000 per person. Compensation does not include amounts paid to undocumented workers or 1099 payments. Special rules apply to specific types of businesses, including management companies and managed entities;
  4. Fourth, the business determines the lower of three separate calculations; (1) total revenue minus cost of goods sold (i.e., the cost of goods sold method), (2) total revenue minus compensation (i.e., the compensation method), or (3) total revenue multiplied times 70% (i.e., the 70% method). The business elects each year to use the method that results in the lowest margin;
  5. Fifth, the business apportions its margin as between Texas and other states in which it conducts business; and
  6. Sixth, the business subtracts other allowable deductions specifically granted by the margin tax statute.

Combined Groups and Tiered-Partnership Arrangements

The margin tax statute requires combined groups to file on a combined group basis. This reporting rule represents a significant change from the old franchise tax law that prohibited consolidated reporting. Combined groups are affiliated entities, whether corporate or non-corporate, that have 80% common control and are engaged in a so-called unitary business. A unitary business generally includes separate parts of a single entity or a controlled group of entities that, in either case, constitute a single economic enterprise by reason of interdependent and integrated business activities.

The margin tax statute permits a form of combined reporting for tiered partnership arrangements. A tiered partnership arrangement includes partnerships that are 100% owned by one or more other taxable entities and may consist of one or more tiers. In this case, the other taxable entities may pay and report the margin tax attributable to their respective ownership interests in the partnership.

Tangling with the Texas Margin Tax

Businesses must assess the business, legal and tax implications resulting from the Texas Margin Tax. Business structures need to be viewed (and perhaps revisited) in light of the fact that most limited partnerships are now taxable. Tax planning needs to be revamped to carefully consider the different methods used to calculate the margin tax, how to maximize the benefits of each method and how to minimize margin tax liability. Tax reporting will need to be revised to include combined groups and, as appropriate, tiered partnerships.

This article is for general information purposes only and is not intended to constitute legal or tax advice and should not be viewed as such. Readers are encouraged to consult with their attorney or tax advisor to consider the matters discussed in this article in light of their unique tax circumstances. ©2007

Read more by Jay D. Crutcher

Tags:  Featured  May-June 2007 

Share |
PermalinkComments (0)

What are you paying for electricity? Part 2, Residential Electric Rates

Posted By David Young, Tuesday, May 01, 2007
Updated: Sunday, February 10, 2013

To protect your and your company’s wallets, it is very important to understand the rates for which you are being charged for electricity. To get your feet wet, I am going to share with you and discuss in detail the electric rates of a typical utility. The example I am using is a utility that publishes their rates on the Internet. The electric rates for which you are being billed may vary greatly from my example. I recommend that you contact your utility to get a copy of your rate and find out what other rates are available to you. In most states, if a residential, commercial or industrial establishment wants electric service, they do not have a choice as to the service utility. In some states, customers have a choice as to the utility from which they purchase their energy. This utility is sometimes called the supply utility. The supply utility may be the same or a different one from the service utility. To accommodate these two functions, some electric utility rates have two components, one called delivery charges and the other called supply charges. Customers pay the delivery charges of their service utility and the supply charges of the supply utility.

Photo 1. Residential Meter

I understand that most customers have chosen to have the same utility for both functions. If utilities other than your service utility offer supply in your state, compare the supply charges of the two utilities. You might be able to save some money by changing to a different supply utility.

To keep things simple in my discussion of rates, I am not going to show the delivery and supply charges separately. Imbedded in most delivery charges is a customer charge. The customer charge is usually a minimum bill associated with having electric service.

Basic Residential Rate

For our example utility, the basic residential rate has a customer charge of $7.36 per month and the total energy charge is 13.1456 cents per kWh for the summer months June through September and 14.3249 cents per kWh for the first 500kWh and 12.6017 cents per kWh for the excess over 500kWh for the winter months October through May. For this rate there is not much one can do to save money except to turn off lights and appliances when not in use. For a residence that uses 1000 kWh of energy each month, the bill would be $141.99 per month in the winter months and $138.82 per month in the summer months. The annual cost would be $1691.20 on this rate. For this rate, the supply charges are about 76% of the total bill.

Residential Electric Heat Rate

Some utilities offer a special rate for residences where the primary source of heat is electric resistance heat or electric heat pump. For our example utility, the customer charge for this rate is $7.36 per month and total energy charge is 14.1284 cents per KWh for the summer months June through September, and 15.5948 cents per kWh for the first 500kWh and 8.6716 cents per kWh for the excess over 500kWh for the winter months October through May. Obviously, the big savings in this rate is the 8.6716 cents per kWh for the winter months. For a residence that uses 1000 kWh each month in the summer months and 2000 kWh per month in the winter
months, the annual cost would be $2317.86 on this rate. If the customer originally had oil or gas heat and then switched to electric heat but did not notify the electric utility to change them to the electric heat rate, the annual cost would be $2699.34 on the basic residential rate. I have heard of customers paying the higher rate for years before they realized their error. I am sure there are customers who still pay the higher rate.

Table 1. Basic Residential Rate

Residential Time-of-Use Rate

Some utilities offer a rate where the cost of energy changes with the time of day. For our example utility, the customer charge for this rate is $11.32 per month and the energy charge during the summer months is 22.8253 cents per kWh during on-peak hours of the day and 6.58390 cents per kWh during off-peak hours of the day. On-peak hours are 9:00 a. m. to 8:00 p. m. Monday through Friday. During Daylight Savings Time, on-peak hours are 10:00 a. m. to 9:00 p. m. Monday through Friday. During the winter months, the energy charge is 22.7142 cents per kWh during on-peak hours of the day and 7.6336 cents per kWh during off-peak hours of the day. To accomplish the metering function for this rate, the utility installs a sophisticated electronic meter that has a built-in computer. The computer has a very accurate clock and keeps track of how much energy is used during the on-peak and off-peak time periods of each day.

Table 2. Residential Electric Heat Rate

Note the huge price difference between on-peak and off-peak charges. If your work schedule is such that you are only home from 8:00 p. m. to 9:00 a. m. and you turn off your heat (winter) and air-conditioning (summer) when you are not home, you could save a bundle. If you get home at 6 p. m., the savings may not be as much, particularly if you use an electric stove. On the weekend, you do not have to change your lifestyle since you are on the cheap rate all weekend.

Residential Time-of-Use With Demand Rate

Some utilities offer a time-of-use rate where the customer is charged for energy and demand. You will recall from part one, peak demand is the peak power and is based upon the maximum instantaneous current.

Table 3. Residential Time-of-Use Rate

A family comes home from the beach on a hot summer day. Mom turns on the air-conditioner because the house is hot. Dad goes to the refrigerator and chest freezer and stands there with the door open for five minutes trying to decide what to cook for supper. Both units turn on. Dad turns on the oven and two burners of the electric stove to cook supper. Oldest daughter jumps into the shower. The electric hot water heater turns on. Mom throws most of the beach clothes into the washing machine. The son decides to dry his beach towels without washing them. Now the electric clothes dryer is on. Oldest daughter gets out of the shower and finds cold air coming out of the air-conditioner vent. She turns on the electric wall heater in the bathroom while she dries her hair with a hair dryer the size of a chain saw.

Would you believe 100 amps at 240 volts? That is 24,000 Watts (24 kW) peak demand. Since a 60-minute demand is the average power used for a 60 minutes period and it is not likely that all the appliances would be on for a full hour, the 60-minute demand will probably be less. That may not be true if you have six teenagers.

Table 4. Residential Time-of-Use with Demand

For our example utility, the customer charge for this rate is $11.32 per month and the energy charge during the summer months is 7.3405 cents per kWh during on-peak hours of the day and 5.4510 cents per kWh during off-peak hours of the day. For this rate, on-peak hours are 8:00 a. m. to 9:00 p.m Monday through Friday. During Daylight Savings Time, onpeak hours are 9:00 a. m. to 10:00 p. m. Monday through Friday. During the winter months, the energy charge is 8.5299 cents per kWh during on-peak hours of the day and 6.2911 cents per kWh during off-peak hours of the day. The demand charge is $10.493976 per kW during the summer months and $9.982711 per kW during winter months.

The billing demand during the summer months is the greatest demand established during any 60-minute clock hour of the month, during on-peak hours, taken to the nearest whole kW. The billing demand for each of the winter months is the greater of the maximum demand established during any 60-minute clock hour of the month, during on-peak hours, taken to the nearest whole kW or 75% of the greatest billing demand as created during the most recent summer billing months.

It is easy to see that the energy charges are low for this rate but the demand charge can kill you. At $10.49 per kW, this rate might not be a good choice for the family who goes to the beach each month. I think that the complexity of this rate is one reason why very few people switch to this rate. As I suggested with the nondemand time-of-use rate, if you are only home between 8 p. m. and 9 a. m. each day this rate might save you a lot of money.

Next time, in Part 3, I will get into the details of the rates that apply to commercial and industrial facilities.

Read more by David Young

Tags:  May-June 2007  Other Code 

Share |
PermalinkComments (0)

Allowable Ampacities – Conductors in Cable Trays

Posted By Leslie Stoch, Tuesday, May 01, 2007
Updated: Sunday, February 10, 2013

In my experience, a discussion of conductor numbers and ampacities in cable trays is frequently met with a snicker or knowing smile. Could it be that the rule for wiring in cable trays is sometimes taken less than seriously? We have all seen trays overloaded with cables, if not at the time of installation, then in the fullness of time. Once the trays are in place as originally designed, it’s far too easy to add cables, especially when the trays follow a convenient route to the end destinations of the added cables.

Occasionally, people are surprised that there is a rule for cable trays and that it can greatly increase the minimum conductor sizes given in Tables 1 to 4. So in this article, let’s review the much maligned Canadian Electrical Code Rule 12-2210, Ampacities of Conductors in Cable Trays.

We will take a detailed look at the maximum permissible ampacities for conductors installed in ladder, ventilated and non-ventilated cable trays. For those of us less familiar with cable trays, Section 0 includes some very precise definitions for all three types. But for our purposes, it’s enough to know that all have side rails and a bottom. The bottom of a ladder tray looks something like a ladder where the spacing between the rungs exceeds 50 mm. A ventilated tray has a solid bottom that has ventilation openings not exceeding 50 mm in longitudinal length. A non-ventilated tray is totally enclosed on the top, bottom and both sides with no ventilation openings.

CEC Rule 12-2210 prescribes that when installed in a cable tray, allowable conductor and cable ampacities are based on Tables 1 to 4 for copper and aluminum conductors with adjustments based on the spacings between cables and the type of tray selected.
When spacings between cables in a ladder or ventilated tray are maintained at greater than 100 percent of the largest cable diameter in the tray, the minimum conductor ampacities may be determined from:

  • Tables 1 or 3 for copper or aluminum single-conductor cables; or
  • Tables 2 or 4 for copper or aluminum multiple-conductor cables, ampacities corrected in accordance with Table 5C for the number of conductors when they exceed three per cable.

For example, with 100 percent of the largest cable diameter spacing maintained, a cable that contains six current-carrying conductors would require a correction factor of 80 percent based on Table 5C, applied to the ampacities derived from Tables 2 or 4.
When spacings between cables in a ladder or ventilated tray are maintained at any distance between 25 percent and 100 percent of the largest cable diameter in the tray, the allowable ampacities obtained as above would need to be further corrected in accordance with Table 5D unless a deviation from the rule is permitted. Table 5D is arranged in up to six conductors or cables arranged horizontally and two rows vertically.
If for example we decide to install a single layer of five cables horizontally in a ladder or ventilated tray, spaced at 50 percent of the largest cable diameter apart, the allowable ampacity as determined from above example would need to be reduced to 83 percent in accordance with Table 5D.

But hold on—the most exciting part is yet to come! When cable spacing in a ladder or ventilated tray is less than 25 percent of the largest cable diameter in the tray or for any spacings in a non-ventilated tray, the allowable cable ampacities are based on Tables 2 or 4 for copper or aluminum conductors corrected in accordance with Table 5C for the total number of conductors in the tray.

Let’s say for example we have four 3-conductor cables in a ladder tray, spaced less than the 25 percent of the largest cable diameter apart. And let’s suppose that all of the conductors are considered as current-carrying as defined in the CEC. This would give us twelve conductors in the tray. Table 5C shows that the allowable ampacities of the cables in this tray would need to be corrected to 70 percent of their Table 2 or 4 ratings. No doubt everyone faithfully applies Table 5C as shown in this example at every given opportunity.

At the end of Rule 12-2210, there is a reminder that the cable ampacities must be further reduced when the trays are installed in a location where ambient temperatures may exceed 30ºC. For example, when installing 90ºC rated conductors in a location where the ambient temperature may reach 40ºC, a further correction to 90 percent of the above calculated values would be necessary.

As with earlier articles, you should always consult the electrical inspection authority in each province or territory as applicable for a more specific interpretation of any of the above.

Read more by Leslie Stoch

Tags:  Canadian Code  May-June 2007 

Share |
PermalinkComments (0)


Posted By James W. Carpenter, Tuesday, May 01, 2007
Updated: Sunday, February 10, 2013

There are signs all around us telling us what to do, warning us of danger, and some we are not aware of until it is too late. There are all kinds of signs along the roads we drive on, telling us to stop, merge, or curve ahead. Speed limit signs—I suppose many of you can relate instances where nobody seems to obey the posted speed—are also seen along the roads we travel. We know the signs of spring; the grass turns green, the trees bud, and the flowers bloom. We are aware of all the seasons of the year by the signs we recognize. If we are knowledgeable of the signs emanating from our spouses and loved ones, we should be able to tell if they have had a bad day and act accordingly. Yes, there are signs all around.

Many of us belong to organizations, clubs, or associations, whether it is for business, fellowship, or just to be a member of a group. There are many reasons we want to align ourselves with the groups, be it the cause or maybe we just like the people. For the past two issues of the IAEI News I have asked you to consider why you are in the electrical trade and why you are an IAEI member. This time let us examine why you are a member of the local chapter or division of IAEI. Probably your first thought would be, because this is the area where I live or work. But let’s get deeper. Why do you participate in your local chapter or division? Or maybe the question should be, "Why don’t you participate?”

It has been said, "You get out what you put in.” That can be said for IAEI. While IAEI provides many opportunities for expanding your knowledge of the codes and standards, it also provides many other opportunities for you to broaden yourself. Maybe you wish to broaden your leadership skills. Offering to serve on committees, or sharing your knowledge with others by teaching and conducting educational programs are ways of participating in divisions, chapters, or sections activities.

What are the signs of a good chapter? What makes people want to come to chapter meetings or chapter-sponsored educational programs? There are several chapters and divisions in IAEI that are having successful meetings with increasing attendance. They have found that programs designed to keep abreast of the latest in the changing codes and standards are paying off with increased attendance. They have found new and different ways of presenting their message and are keeping the meetings and workshops fresh. These active chapters are increasing their membership while others are decreasing. IAEI needs more chapters and divisions to seek out what constituents want and institute programs to fill those wants and needs. This will surely stem the loss of members and return IAEI to a growing association. Government leaders listen when a strong and growing organization has a voice on all areas of electrical safety.

Some of IAEI’s chapters are not doing things that keep people interested and coming to meetings. What are the signs of those chapters? Is the leadership stagnant? Are the programs, if there are any, relevant? The International Office has received concerns about some chapters’ leadership not being receptive to the members’ needs. Some chapters are not even having meetings where the members can elect their officers. Some don’t even know who their officers are. We hear that only the officers can attend the meetings or only a certain type of member can attend. These are certainly signs of a chapter not adhering to the goals that our founders established nearly eighty years ago. What can be done? We must learn the lessons that the successful chapters have learned. To do that, you the member at the local level must tell the story. Make sure your chapter secretary gets the minutes of your meeting in the IAEI News so that others can see what is working for your chapter. We would very much like to print your personal story of why you are an electrical professional, why you are a member of IAEI, and why you participate at the chapter or division level. If you have reasons for not participating, then maybe you could get involved and change the under-performing or non-performing chapter into a viable and valuable chapter where people just can’t wait for the next meeting. Give us your thoughts on the signs you see.

Read more by James W. Carpenter

Tags:  Editorial  May-June 2007 

Share |
PermalinkComments (0)

Are all split bolt clamps Listed to be used for connecting copper grounding electrode conductors to steel rebar direct buried in earth, and if so how can these clamps be identified?

Posted By Underwriters Laboratories, Tuesday, May 01, 2007
Updated: Sunday, February 10, 2013

Question: Split bolt clamps

Are all split bolt clamps Listed to be used for connecting copper grounding electrode conductors to steel rebar direct buried in earth, and if so how can these clamps be identified? Have they been investigated to ensure there are no electrolysis problems related to the dissimilar metals involved?


Typical split bolt connectors are not Listed for connection of a grounding electrode conductor to rebar, they are intended for connection of two conductors in an ordinary dry location inside an enclosure and are Listed under the category Wire Connectors, (ZMVV) located on page 307 in the 2006 UL White book or online entering ZMVV at the Category Code Search. These type of split bolts connectors are not intended to be used for grounding applications to connect a grounding electrode conductor to rebar or any other component of the grounding electrode system. The Listing Mark on the connector or packaging would identify it as a wire connector.

Split bolt connectors evaluated for grounding applications as well as other types of grounding clamps are Listed under the product category Grounding and Bonding Equipment, (KDER) located on page 122 in the 2006 UL White Book or online entering KDER at the Category Code Search. As part of the Listing evaluation of a grounding or bonding device, they are required to be constructed of a metal or metals that, when the device is installed under conditions of actual service and exposed to moisture, will not be likely to be adversely affected by electrolysis.

Clamps Listed under Grounding and Bonding Equipment (KDER) are evaluated for compliance with The Standard for Grounding and Bonding Equipment, UL 467. A grounding or bonding device marked as acceptable for burial in earth or embedment in concrete shall be provided with all screws necessary for assembly or connection of the device, and shall be constructed of copper or a copper alloy containing not less than 80 percent copper, or stainless steel.

Grounding-type split bolt clamps or connectors Listed for use with rebar will be marked on the connector or a tag on the connector identifying the size range of the rebar and conductor size the device was Listed for use with. In addition, connectors Listed for direct burial in earth or encased in concrete are marked "DB” or "Dir Bur.” The Listing mark on the product, or on a product tag or product container will identify the product as grounding and bonding equipment.

Read more by UL

Tags:  May-June 2007  UL Question Corner 

Share |
PermalinkComments (0)

Does UL List the spiralshaped compact fluorescent lamps (e.g. light bulbs)?

Posted By Underwriters Laboratories, Tuesday, May 01, 2007
Updated: Sunday, February 10, 2013

Question: Spiralshaped compact fluorescent lamp

Does UL List the spiralshaped compact fluorescent lamps (e.g. light bulbs)? Can they be used in any type of light fixture including recessed-type incandescent fixtures?


UL does List the spiral shaped types of compact fluorescent lamps (CFLs) that are very popular right now. These types of lamps consist of a self-contained fluorescent tube and ballast in an enclosure with a medium base screw shell adapter that will screw into any medium base lamp holder. This category also covers self-ballasted lamps employing light emitting diode (LED) lights. These products are Listed under the product category Lamps, Self-Ballasted and Lamp
Adapters, (OOLR) located on page 169 of the 2006 UL White Book or online entering OOLR in the Category Code Search.

This category covers fluorescent self-ballasted lamps that incorporate a non-replaceable light source and lamp adapters for use with a replaceable light source, for installation in Edison base lamp holders in incandescent luminaires and portable lamps operating at 120 V 60 Hz nominal.

This category also covers selfballasted lamps and lamp adapters intended for installation in other ANSI base type lamp holders for operation on other voltages as marked on the product.

Products with fluorescent lamps in this category are provided with integral protection that prevents overheating and which meets the requirements of Underwriters Laboratories Inc. for Class P fluorescent lamp ballasts.

Products are marked to indicate the environmental conditions for which they have been evaluated: dry, damp or wet locations.

Unless evaluated for use in totally enclosed recessed luminaires or for use with a dimmer, these products are required to be marked "Not for use in totally enclosed recessed fixtures,” and "Not for use with dimmers.”

The wattage rating on compact fluorescent lamps is typically much less than the incandescent lamp they are replacing. A compact fluorescent lamp rated 13 watts emits the equivalent light output of a 60-watt incandescent lamp and a 42-watt compact fluorescent has the equivalent output of a 150-watt incandescent lamp with a fraction of the heat that is generated from the incandescent lamps.

As long as the wattage on the compact fluorescent lamp is equal to or less than the relamping marking on the luminaire that the lamp is going into, then the compact fluorescent lamp can be used in the luminaire, provided all the markings on the compact fluorescent lamp are complied with. Compact fluorescent lamps run much cooler than incandescent lamps and do not present a heat issue with recessed luminaires.

These products are not intended for use in emergency lighting equipment or exit fixtures.

Tags:  May-June 2007  UL Question Corner 

Share |
PermalinkComments (0)

Getting Down to Earth

Posted By Michael Johnston, Thursday, March 01, 2007
Updated: Sunday, February 10, 2013

From the beginning, the National Electrical Code has included specific rules that are essential for protection of persons and property. Wiring and protection is covered more specifically in chapter 2 and is so titled. Article 250 provides the specific rules for grounding and bonding electrical systems and equipment. To understand how the grounding and bonding rules apply to electrical installations, one must establish a thorough knowledge of how grounding and bonding functions from a performance standpoint. In other words, what is intended to be accomplished when a rule requires grounding, and what must be accomplished when the Code requires bonding? (see figures 1 and 2).

Figure 1. Grounding means connected to the earth.

Figure 2. Bonding means connected together

Both grounding and bonding are fundamentally necessary for electrical safety. This article provides a look at extensive work completed over a period of approximately one year that resulted in significant improvements in understandability and usability in the NEC specifically related to grounding and bonding rules. It should be understood that as of this writing, the NEC Technical Committees have completed their work on all proposals and comments for the 2008 NEC, but this work could still be impacted by any appeals that may be filed in accordance with the NFPA Regulations Governing Committee Projects.

Figure 3. Purpose of the equipment grounding conductor is to ground equipment and provide an effective path for ground fault current.

Proposal 5-1 in the 2004 NEC Report on Proposals created quite a stir during the code development process in the 2005 NEC cycle. This proposal introduced a concept of changing the defined term equipment grounding conductor to the term equipment bonding conductor. This is where it all started. The substantiation with the proposal clearly identified some points that warranted serious consideration. As one can imagine, this proposal was met with a wide variety of reactions. Such a proposed change in the NEC flies in the face of tradition and faced skepticism and resistance. Many Code traditionalists saw this proposal as unnecessary and a change that would create confusion and unnecessary work in many other industry and product standards, which is definitely understandable. Others viewed this proposed change with optimism and an open-minded approach to the concepts, and realized the proposed revisions were technically correct in several ways. The challenges presented were similar to those that the industry faced when grounding and bonding rules were first developed. It was clear, based on the initial reaction of nineteen of the code-making panels, that the proposal had merit. Additionally, this proposal identified necessary revisions to defined grounding and bonding words and terms in Article 100. The proposal was ultimately rejected and the change never happened in the 2005 NEC; however, this proposal generated considerable interest and concern from the members of code-making panel 5, which is responsible for Articles 200, 250, 280, and 285. After much deliberation and discussion about this concept and some identified areas in need of improvement, it was determined that the chairman of CMP-5 would recommend to the NEC Technical Correlating Committee (TCC) that a special task group be assembled to explore all of the defined words and terms related to grounding and bonding and verify their accuracy and functionality, and to review their use in Article 250 and other rules throughout the entire Code. The recommendation was viewed favorably by the correlating committee resulting in a TCC assigned Task Group on Grounding and Bonding. A task group chair, who was also a representative of the TCC, was appointed to lead this group in achieving their established set of specific objectives. This provided an excellent conduit for continuous communication and observations by the TCC of the work and progress. The task group was then assembled including seven key members of CMP-5 along with several other key members of other NEC technical committees. There were also two members of the Technical Correlating Committee included in this working group which totaled 18 members.

Photo 1. Bonding through conduit or tubing fittings

The Task Ahead

The Technical Correlating Committee provided clear directives to explore several significant issues identified in Proposal 5-1 and Comment 5-1 in the 2005 NEC cycle regarding grounding and bonding terminology defined and used the Code. The following represents the scope of the assigned Task Group on Grounding and Bonding.

  • To explore the issues identified by Proposal 5-1 and Comment 5-1 in the 2005 NEC cycle
  • To consider developing proposals for the 2008 NEC to establish consistent use of the terms grounding and bonding as discussed in the identified proposals and comments during the 2005 NEC development process
  • To consider other codes and standards, such as the Canadian Electrical Code (CE Code), Part I and International Electrotechnical Commission (IEC) 60364 in an effort to harmonize the definitions and use of the terms grounding and bonding
  • To consider the inter-relationship of the NEC with product standards and the National Electrical Safety Code (NESC)

Common Understanding

Figure 4. Equipment grounding conductors perform bonding and grounding functions.

Before the work could begin, it was important to get all members of the group on the same level of understanding. One of the most important tasks for this working group was to establish a clear and common understanding of all defined grounding and bonding words and terms. Another essential objective of this group was to review the performance requirements provided in 250.4. Section 250.4(A) and (B) provide the descriptive performance objectives of grounding and bonding. As the work began, it was clear that not all members in the group viewed grounding and bonding in the same fashion, and these members all carry extensive levels of Code experience. The result was a meaningful open dialog for all task group members to share ideas and benefit from each other’s input and experience. The first few months of work were necessary to establish this common understanding before any productive work could begin in achieving the established objectives of the assignment. Each member of the working group quickly realized that not everyone has the same understanding of grounding and bonding, which is also the case in the electrical industry as a whole. For this work to be productive and of benefit to the NEC, progressive thinking and being open to sharing all ideas became an eye-opening realization for the group.

Rules Using Defined Words and Terms

Table 1. Revised grounding and bonding defined words and terms

The definitions in the NEC assist users with proper application of the rules. The Code rules should mean what they imply by definition. When defined words and terms are not used consistently within the rules, it can lead to inconsistent and incorrect application of the requirements. With everyone in the group on the same page, the task of reviewing each of the defined grounding or bonding words and terms was underway. It was soon realized that some definitions needed revision, another was considered for deletion, and new ones were considered. Table 1 shows a a summary of the grounding or bonding words and terms that were affected by the work of this task group.

Photo 2. Bonding using equipment bonding jumpers

The work of the task group on these defined words and terms was primarily in an effort to reduce the definitions to their simplest form. As the work progressed, it was soon realized that many of these definitions were not accurate, and included performance requirements that were already contained in other performance requirements incorporated into 250.4. Keeping defined words and terms in a simple form helps assure that where these words or terms are used in Code rules, they will be accurate in meaning. In recent editions of the NEC, clear performance text was incorporated into Article 250 that explains the purpose of grounding and bonding. With this understanding, the task group realized that keeping the defined words and terms in their simplest form would be beneficial in the essential code-wide work that would follow. The following are the revised definitions of the grounding and bonding words or terms provided in table one.

Article 100 Definitions

Bonded (Bonding).Connected to establish electrical continuity and conductivity.
Ground. The earth.

Grounded (Grounding).Connected (connecting) to ground or to a conductive body that extends the ground connection.

Grounded, Effectively.Definition was deleted because the term is subjective and there are no specific parameters to use in making determinations as to whether or not an entity is effectively grounded. Instances where it was used in previous editions of the Code have been revised to remove the word "effectively” from the phrase. The term grounded, by definition, means connected to the earth. The direct connection to the earth through grounding electrodes is not always effective and varies based on geographical location or seasonal conditions and so forth. The word "effective” is used in the performance rules in Section 250.4 that relate to the effectiveness of the ground-fault current path necessary to facilitate overcurrent device operation, which is appropriate, measurable, and remains unchanged as a result of deleting the definition. The term effectively bonded, which was never defined, was also revised to remove the word "effectively” from the phrase. The performance criteria for bonding and what it is intended to accomplish is already provided in Section 250.4 and 250.90. There are conditions covered by the Code where bonding is required solely to minimize differences of potential between conductive parts such as for health care facilities, swimming pools and similar installations, agricultural buildings, and so forth. The definition of bonding has been revised to simplify its meaning as covered above.

Grounding Electrode.A conductive object through which a direct connection to earth is established.

Grounding Electrode Conductor.The conductor used to connect the grounding electrode(s) to a system conductor or to equipment.

Grounding Conductor, Equipment (EGC).The conductive path installed to connect normally non-current-carrying parts of equipment together, and to the system grounded conductor or to the grounding electrode conductor, or both.

FPN No. 1: It is recognized that the equipment grounding conductor also performs bonding.

FPN No. 2: See 250.118 for a list of acceptable equipment grounding conductors.

Ungrounded.Not connected to ground or to a conductive body that extends the ground connection.

Section 250.2 Definition

Ground Fault.An unintentional, electrically conducting connection between a normally current-carrying conductor of an electrical circuit and the normally non–current-carrying conductors, metallic enclosures, metallic raceways, metallic equipment, or earth.

FPN: Unintentional grounding connections to the grounded conductors on the load side of the service disconnecting means or the load side of a separately derived system, creates one type of ground fault condition addressed in the definition of ground fault.

Responsibilities for Definitions

Photo 3. Connection to ground through a grounding electrode conductor

Sometimes timing is everything. The 2008 NEC development process included a shift in responsibility for any technical definitions that fall under the scope of responsibility of certain NEC technical committees. Traditionally, all of the definitions in Article 100 were the responsibility of code-making panel 1. Action by the NEC Technical Correlating Committee (TCC) results in each code-making panel being responsible for definitions of words and terms that are under their responsibility, but these definitions will continue to be located in Article 100. Definitions that are general in nature will continue to be assigned to code-making panel 1. As a result, CMP-5 was responsible for reviewing and acting on all proposals to revise definitions of grounding and bonding words and terms. The panel acted favorably to all definition revisions that resulted from the work of the task group.

Code-Wide Improvements

Table 2. Summary of proposals submitted by the task group

The work of TCC Grounding and Bonding Task Group also included a global NEC review and analysis to address how each of the grounding or bonding words or terms were used in Article 250 and submit proposals for necessary revisions as required. The task group had the responsibility to specifically address how each word or term was currently being used throughout the rest of the rules in the Code. Where revisions were necessary, the task group developed and submitted proposals to each NEC Technical Committee. In many cases, revisions were made to include more specific direction and prescriptive language for users that clarifies what is meant by a rule that includes the words "shall be grounded.” The accepted changes in this instance resulted in changing the term shall be grounded to shall be connected to an equipment grounded conductor where that was the original intention of the requirement. This resulted in better Code that is not subjective and is understood and enforceable. The Grounding and Bonding Task Group developed 28 proposals for the 2008 NEC as provided in table 2.

Each of the code-making panels acted favorably to the proposals resulting from the efforts of the task group; however, not all of the proposals were accepted without some modification. There were some instances where each technical committee had to accept in principle the proposed revision and make slight adjustments necessary for specific functionality. The efforts to make such extensive code-wide revisions involved all of the NEC technical committees embracing the concepts and efforts put forth by the Task Group on Grounding and Bonding.


Photo 4. Ungrounded portable generator

People are generally resistant to change, which is human nature. Breaking tradition is more difficult for some than others. Sometimes change is necessary and meaningful. In the electrical code-making process, change is continuous because of the inherent dynamics of the NEC. Changes should never be made just for the sake of change; there must be purpose (reason), an objective (goal), and a positive result (good code). Good code is code that is understandable, practical, and enforceable. The 2008 Code has experienced a series of changes related to grounding and bonding definitions and rules. The concepts and objectives of these revised definitions and rules are retained, clarified, and improved as a result of extensive work by an assigned group of many dedicated professionals to achieve these objectives. See IAEI’s book, Analysis of Changes 2008 NEC for additional information about these and many other significant changes ultimately incorporated into this new edition of the Code.

Read more by Michael Johnston

Tags:  Featured  March-April 2007 

Share |
PermalinkComments (0)

Overcurrent Protection, Part 1

Posted By Tim Crnko, Thursday, March 01, 2007
Updated: Sunday, February 10, 2013

This article provides readers with essential information about basic operation and basic time-current characteristics of branch-circuit-rated, low-voltage fuses and circuit breakers. These overcurrent protective devices (OCPDs) are typically used in main service disconnects, feeders and branch circuits of residential, commercial, institutional, and industrial electrical systems. There are other OCPDs used, such as relays and supplementary OCPDs, which this article does not directly address. However, many of these principles presented also apply to the other types of devices. This article explains the basics, and as you might suspect, there are product designs for fuses and circuit breakers where the operation principles are more complex and may deviate from what is presented. However, you need to walk before you run. Part II, which will be in the May/June issue, will cover important information regarding OCPD ratings, application in designs, and NEC compliance aspects.

Why Is Overcurrent Protection So Important?

Figure 1. Oscillograph representation of a fault

The author remembers having a conversation some years ago with a well-known industry expert who is very knowledgeable in the National Electrical Code. This expert views grounding and bonding and overcurrent protection as the two most important protective principles in the Code. Grounding and bonding is important for two reasons: (1) improper grounding and bonding can kill people and pose a fire hazard and (2) adequate grounding and bonding helps ensure the overcurrent protective devices operate in a reasonable time by providing a low impedance and effective path for fault current. Overcurrent protection is important to the overall objective of electrical safety. If the designer, installer, maintainer or inspector does not get overcurrent protection right, there can be the threat of fires and personal safety hazards due to (1) long-time thermal ignition of materials from improper overload protection, (2) explosive ignition and flash hazard from improper short-circuit protection or (3) the explosive ignition and flash hazards from improper voltage-rated or improper interrupting-rated overcurrent protective devices.

Figure 2. Example of fuse time-current characteristics

The proper selection of overcurrent protective devices entails many considerations, some mandatory and some discretionary. The mandatory considerations include complying with NEC requirements and ensuring OCPDs are applied within their ratings and limits per their capabilities, which are typically evidenced by specific product standard listing and labeling [110.3(A)(1)].

Type Overcurrents

OCPDs are intended to protect against the effects of potentially harmful overcurrents. An overcurrent is either an overload current or a short-circuit current, which often is referred to as fault current. Overload current is an excessive current relative to normal operating current, but one that is confined to the normal conductive path provided by the conductors and other components and loads of the distribution system. As the name implies, a short-circuit current is one which flows outside the normal conducting path. Article 100 has definitions for overcurrent and overload. One of the important overcurrent protection principles that typically holds true is that the higher the overcurrent magnitude, the faster the overcurrent must be interrupted.


Figure 3. Example of fuse minimum melt and total clear band

Overloads are most typically between one and six times the normal current level. Most often, they are caused by harmless temporary surge currents that occur when motors start up or transformers are energized. Harmful sustained overloads can result from defective motors (such as worn motor bearings), overloaded equipment, or too many loads on one circuit. Such sustained overloads are destructive and must be cut off by protective devices before they damage the distribution system or system loads. However, since they are of relatively low magnitude, removal of the overload current within a few seconds to many minutes will generally prevent circuit or equipment damage. A sustained overload current results in overheating of conductors and other components and will cause deterioration of insulation, which may eventually result in severe damage and short circuits if not interrupted.

Short-Circuit or Ground-Fault Currents

Whereas overload currents occur at rather modest levels, short-circuit or ground-fault currents occur in a wide range of current magnitude. For instance, a fault may be a lower level ground fault (a high impedance fault between phase and ground), a high-level ground fault (a low impedance fault between phase and ground), a high-level bolted three-phase fault (a low impedance fault between all three phases), or a moderate to high level three- phase arcing fault (a moderate or low impedance fault, through air, between all three phases). Since the load is faulted out of the circuit, the circuit impedance is drastically reduced. Since I (current) = E (voltage) divided by Z (impedance), the resulting lower impedance causes the immediate increase in the current (see figure 1). Fault currents can be many hundreds of times larger than the normal operating current. A high-level fault may be 50,000 A (or larger). If not cut off within a matter of a few thousandths of a second, damage and destruction can become rampant; there can be severe insulation damage, melting of conductors, vaporization of metal, ionization of gases, arcing, and fires. Simultaneously, high-level short-circuit currents can develop huge magnetic-field stresses. The magnetic forces between bus bars and other conductors can be many hundreds of pounds per linear foot; even heavy bracing may not be adequate to keep them from being warped or distorted beyond repair. In the last 10 years or so, the industry has begun recognizing the severe flash hazards and blast hazards to personnel due to arcing fault current.

Time-Current Characteristics

Figure 4. Typical 100A, 600V, Class RK1, dual-element, time-delay fuse

If you understand the physical properties and how the devices operate, you may retain the information better and understand the reasons for specific requirements. The following is a brief, simplified version. There are many types of circuit breakers and fuses, but all follow common, basic principles.

Figure 5. Overload operation

Let’s start with the principle that OCPDs are intended to continuously carry the load current, and if there is an overcurrent condition, their purpose is to open in time to prevent extensive damage to the circuit components. This is a requirement under fault conditions in Section 110.10. The allowable speed of response of an overcurrent protective device can vary depending on the magnitude of overcurrent. If the overcurrent is a light overload, it may be permissible to permit the current to flow for many minutes. As a matter of fact, some circuit components, such as motors, primary winding of transformers and capacitors, have harmless high starting or energizing inrush current which can be many times greater than the normal full load current. So the application of OCPDs on these circuits require that the OCPD permit intentional overload currents for a period of time without opening. If the overcurrent is a faulted circuit, rapid OCPD response is desired to minimize circuit component or equipment damage. The examples in figures 2 and 3 illustrate OCPD time-current characteristics via a circuit diagram with ammeter readings and OCPD opening times for various overcurrents. For higher levels of overcurrent, the OCPD operates faster. Also, this example illustrates that the OCPD characteristics can be represented by time-current characteristic curves. See figures 2 and 3, and for the overcurrents depicted in figure 2 determine the opening times from the curve in figure 3. On the time-current curve, the horizontal axis is the amount of current in amperes and the vertical axis is time in seconds. Note: both the current axis and time axis are logarithmic scale, which is the typical representation for OCPD time-current characteristics. The fuse time-current characteristic is properly represented by a tolerance band with the minimum melt curve as the boundary on the left and the total clear curve as the boundary on the right. So for a given overcurrent value, the fuse opening time is represented by a range. For instance in figure 2, the example with a 500 A overcurrent, the fuse will open somewhere between 10 and 17 seconds (see figure 3). Most fuse manufacturers provide minimum melt fuse curves and total clear fuse curves on separate pages. For simplicity, some users just want a fuse represented by a single line curve not a band, so manufacturers may also represent fuses via an average melt curve. An average melt curve, if overlaid, would fall between the minimum melt and total clear curves.

Fuse Operation

Figure 6. During short-circuit operation

Fuse operation is based on basic thermal principles. As current flows through a fuse, the resistance of the fuse element creates heat. If the current is below the amp rating of the fuse, the fuse will carry the current continuously (dependent on sizing per the NEC). In this case, the fuse operates in a thermally stable condition and the internal temperature does not reach a point where the fuse opens. The thermal energy created by the current flowing through the fuse element dissipates to the ambient. In overcurrent conditions, the internal temperature of the fuse elevates; the dissipation of thermal energy is less than the thermal energy created. Whether the fuse opens or how fast it takes to open is dependent on the amount of overcurrent and the duration of the overcurrent condition. The following is a series of illustrations to explain how fuses operate. Shown is a dual-element, time-delay fuse construction. There are other type constructions, but the principles are similar. Figure 4 shows a typical 100 A, 600 V, Class RK1, dual-element, time-delay fuse which has a 300,000 A interrupting rating. Artistic liberty is taken to illustrate the internal portion of this fuse. The real fuse has a non-transparent tube and special small granular, arc quenching material completely filling the internal space (see figure 4).

Figure 7. After short-circuit current interruption

Figure 5 illustrates how a dual-element fuse operates in the overload range. Under sustained overload conditions, the trigger spring fractures the calibrated fusing alloy and releases the "connector.” The insets represent a model of the overload element before and after. The calibrated fusing alloy connecting the short-circuit element to the overload element fractures at a specific temperature due to a persistent overload current. The coiled spring pushes the connector from the short-circuit element and the circuit is interrupted.

Figure 8. Example of current-limitation for fault current

Figures 6 and 7 illustrate a fuse operation in the short-circuit current range. A short-circuit current causes the restricted portions of the short-circuit element to vaporize and arcing commences (figure 6: the arcing is depicted by animation). The arcs burn back the element at the points of the arcing. Longer arcs result, which assist in reducing the current. Also, the special arc quenching filler material contributes to extinguishing the arcing current. The clearing time of a fuse under short-circuit current conditions is the time it takes to melt or vaporize the fuse element’s restricted portions plus the arcing time. The time to melt or vaporize depends on the fuse design and current magnitude. The time duration from the point of the fuse element melting or vaporization until the current is interrupted is rather fast. Typically, this time will be a fraction of a half cycle. For current-limiting fuses in their current-limiting range, the total time to clear is ½ cycle or less (melting plus clearing).

Figure 9. Illustrates various fuse characteristic curves

The special small granular, arc-quenching material plays an important part in the interruption process. Figure 7 shows an actual photo of the internal fuse element after interrupting a fault. The filler assists in quenching the arcs; the filler material absorbs the thermal energy of the arcs, bonds together and creates an insulating barrier. This process helps in forcing the current to zero. It is this entire process that enables fuses to be current-limiting. What does this mean? When the fault current is in the fuse’s current limiting range, the fuse cuts-off the current before it reaches its first peak current value by vaporizing the restricted portions of the fuse element. Then the current is forced to zero via the process with arcing and the filler quenching the arcing before the first ½ cycle of the fault current. Current-limitation greatly reduces the energy that is released in the circuit (see figure 8).

The interruption process is critical for a fuse. To have sufficient voltage rating and interrupting rating a fuse must be designed properly. Critical in achieving a specific voltage rating are the number of restricted portions or neck-down sections in series. For the fuse shown in this example, there are five restricted portions in series and this fuse is rated 600 Vac. If this fuse were misapplied in a 1500 V circuit and the fuse tried to interrupt, the arcing at the restricted portions would probably continue until so much energy was released that the fuse could violently rupture. There are not enough restricted portions in series for this 600 V fuse to interrupt 1500 V. Similarly, when a fuse attempts to interrupt high fault currents, the fuse must be designed to withstand the tremendous pressure produced inside the fuse body as a result of the rapid vaporization and arcing of a portion of the fuse element. If a fuse tries to interrupt a fault current greater than its interrupting rating, the fuse can violently rupture. Section 110.9 requires that the available short-circuit current at the line terminals does not exceed a fuse’s interrupting rating or a circuit breaker’s interrupting rating. This is a matter of safety.

Figure 10. Circuit breaker operating functions

Several different fuse characteristic types have evolved over the years, each having different time-current characteristics and different degrees of current-limitation under short-circuit conditions. For instance there are non-time-delay fuses (for non-inductive loads), time-delay fuses (for motor loads and now used for most general-purpose applications and even static loads), high-speed fuses (often referenced as semiconductor fuses used for the protection of power electronics). Figure 9 illustrates the minimum melt time-current curve characteristic for three 100 A, 600 V fuse types:

  1. High-speed fuse
  2. Class J time-delay fuse
  3. Class RK5 time-delay fuse

Circuit Breaker Operation

Circuit breakers are mechanical overcurrent protective devices. All circuit breakers share three common operating functions:

  1. Current sensing means:
    A. Thermal
    B. Magnetic
    C. Electronic
  2. Unlatching mechanism: mechanical
  3. Current/voltage interruption means (both)
    A. Contact parting: mechanical
    B. Arc chutes

To interrupt an overcurrent, the chain of events is significantly different from that of a fuse. First, the circuit breaker senses the overcurrent. If the overcurrent persists for too long, the sensing means causes or signals the unlatching of the contact mechanism. The unlatching function permits a mechanism to start the contacts to part. As the contacts start to part, the current is stretched through the air and arcing between the contacts commences. The further the contacts separate the longer the arc, which aids in interrupting the overcurrent. However, in most cases, especially for fault current, the contacts alone are not sufficient to interrupt. The arcing is thrown to the arc chutes which aid in stretching and cooling the arc so that interruption can be made. Figure 10 shows a simplified model with the three operating functions shown for a thermal magnetic circuit breaker, which is the most commonly used circuit breaker. Also, it should be noted that there are various contact mechanism designs that can significantly affect the interruption process.

Circuit Breaker Overload Operation

Figures 11A and 11B illustrate circuit breaker operation by the thermal bimetal element sensing a persistent overload. The bimetal element senses overload conditions similar to the sensor in a HVAC bimetal thermostat. In some circuit breakers, the overload sensing function is performed by electronic means. In either case, the unlatching and interruption process is the same as illustrated in figures 11A and 11B. Figure 11A illustrates, as the overload persists, the bimetal sensing element bends. If the overload persists too long, the force exerted by the bimetal sensor on the trip bar becomes sufficient to unlatch the circuit breaker. Figure 11B shows that once a circuit breaker is unlatched it is on its way to opening. The spring-loaded contacts separate and the overload is cleared. There can be some arcing as the contacts open, but the arcing is not as prominent as when a short-circuit current is interrupted.

Figure 11a. Circuit breaker senses overload and unlatches


Figure 11b. Circuit breaker contacts open and clear overload

Circuit Breaker Instantaneous Trip Operation

Figures 12A, 12B, and 12C illustrate circuit breaker instantaneous trip operation due to a short-circuit current. The magnetic element senses higher level overcurrent conditions. This element is often referred to as the instantaneous trip, which means the circuit breaker is opening without intentional delay. In some circuit breakers, the instantaneous trip function is performed by electronic means. In either case, the unlatching and interruption process is the same as illustrated in figures 12B and 12C.

Figure 12a. Circuit breaker instantaneous trip sensing and unlatching

Figure 12b. Circuit breaker contacts part and arcing


Figure 12c. Circuit breaker contacts open and fault cleared

Figure 12A illustrates the operation under a short-circuit condition. The high rate of change of the current causes the trip bar to be pulled toward the magnetic element. If the fault current is high enough, the strong force causes the trip bar to exert enough force to unlatch the circuit breaker. This is a rapid event and is referred to as instantaneous trip.

Figure 12B shows that once unlatched, the contacts are permitted to start to open. It is important to understand that once a circuit breaker is unlatched it is designed to open; however, the current interruption does not commence until the contacts start to part. As the contacts start to part, the current continues to flow through the air (arcing current) between the stationary contact and the movable contact. At some point, the arc is thrown to the arc chutes, which stretch and cool the arc. The speed of the contacts opening depends on the circuit breaker design. The total time of the current interruption for circuit breaker instantaneous tripping is dependent on the specific design and condition of the mechanisms. Smaller amp rated circuit breakers may clear in ½ to 1 cycle. Larger amp rated circuit breakers may clear in a range typically from 1 to 3 cycles depending on the design. Circuit breakers that are listed and marked as current-limiting can interrupt in a ½ cycle or less when the fault current is in the circuit breaker’s current-limiting range.

With the assistance of the arc chutes, the current gets interrupted when the current approaches zero in the normal course of the alternating current and the contacts travel a sufficient distance (see figure 12C). There can be a tremendous amount of energy released at the contact interruption path and arc chutes during the current interruption process. Circuit breakers are designed to have specific interrupting ratings at specific voltage ratings. For instance, a circuit breaker may have a 14,000 A interrupting rating at 480 Vac and 25,000 A at 240 Vac. If a circuit breaker is misapplied by installing it in a circuit with an available short-circuit current greater than the circuit breakers interrupting rating, the circuit breaker can violently rupture when attempting to interrupt.

Typical Circuit Breaker Time-Current Curve

Figure 13. 400 A molded case circuit breaker time-current curve

Circuit breaker curves are represented in various formats as time-current curves. Figure 13 illustrates a 400 A molded case circuit breaker curve. This is an older style circuit breaker time-current curve representation and the author has not seen curves published with this much detail in recent time. The newer curves do not provide the unlatching time or unlatching curve for the instantaneous trip. However, this curve format is good for learning how a circuit breaker functions. Once you understand there is an unlatching curve, you can interpret the modern curves to make evaluations, if necessary.

The shaded "Overload Operation” portion represents the characteristics of the overload protection with the bimetal element as described in figures 11A and 11B. Notice the representation is a tolerance band not a line curve. This is similar to the fuse tolerance band. If an overload persists long enough, the circuit breaker is intended to open at some point within that "Overload Operation” band. For instance, a 1000 A overload current would be expected to be interrupted between 70 seconds and 300 seconds (see figure 13).

Figure 14. Circuit breaker with overload protection and short-time delay setting

The shaded "Instantaneous Trip” portion represents the characteristics of the short-circuit protection with the magnetic element as described in figures 12A, 12B, and 12C. The band for a specific level of current represents the time of unlatching, parting of the contacts, and extinguishing the current/arcing. The average unlatching time for the instantaneous trip function is shown as a diagonal line; this corresponds to the unlatching described in figure 12A. Once a circuit breaker is unlatched, it still needs to part its contacts and extinguish the arcing; this corresponds to figures 12B and 12C. For instance, on this 400 A circuit breaker curve, a 10,000 A fault current would unlatch the circuit breaker in 0.0025 seconds. Then the contacts part and the current extinguished within 0.028 seconds (approximately 1½ cycles). Note: figure 13 shows the characteristics from 0.001 to 0.01 seconds to illustrate the circuit breaker’s unlatching characteristics. Most fuse and circuit breaker curves show characteristics from 0.01 seconds and greater.

Figure 15. Circuit breaker with overload protection, short-time delay, and instantaneous trip override

There is a variety of circuit breaker types for different application needs. For instance, there are instantaneous trip-only circuit breakers that are intended for motor branch circuit short-circuit protection. There are circuit breakers that have a short-time delay setting that are used either in lieu of the instantaneous trip element (see figure 14) or in conjunction with an instantaneous trip override (see figure 15).

Conclusion and Part II

The information in this Overcurrent Protection Basics, Part I, provided an understanding of how fuses and circuit breakers operate and on the basics of how to read time-current curves. In the next issue, Overcurrent Protection Basics, Part II, we leverage off this material to look at the important ratings for fuses and circuit breakers and other key important criteria that lay the foundation for a better understanding of overcurrent protection and code-compliance.

Read more by Tim Crnko

Tags:  Featured  March-April 2007 

Share |
PermalinkComments (0)

Compliance with Safe Installations by Using Deviations from the CE Code Requirements

Posted By Ark Tsisserev, Thursday, March 01, 2007
Updated: Sunday, February 10, 2013

The object of the Code is very transparent on the fact that all prescriptive rules of the Code address the objective-based fundamental safety principles of the IEC Standard "Electrical Installations of Buildings”.

This standard, IEC 60364-I, comprises the following types of protection:

  • against electric shock (direct and indirect contact);
  • against thermal effect (high temperature or electric arc);
  • against overcurrent (damage due to excessive temperatures or electromechanical stress caused by overcurrents likely to arise on live conductors);
  • against fault currents (against dynamic and thermal effects of fault currents); and
  • against over-voltage (harmful effects due of a fault between live parts of circuits supplied at different voltages).

Thus, it is quite obvious that the prescriptive requirements of the CE Code represent very focused acceptable means by which objective-based fundamental safety principles of IEC 60364-I may be accomplished. Rules of the installations are well coordinated and correlated between different sections of the Code. Rules of General Sections are applicable throughout the Code, unless they are specifically modified or amended by particular rules of Supplementary or Amendatory Sections. Sections 0 to 16 and Section 26 are considered to be "General Sections”, and other sections are "Supplementary or Amendatory”.

For example, Rule 6-206 (in General Section 6) mandates that a service box must be installed within the building being served, and that the deviation from this requirement may be entertained only under provisions of a special permission.

However, Section 36 (which is amendatory to General Sections) allows outdoor installation of the H.V. service boxes. Another example is Rule 14-104. Although, in general, this rule states that the rating or setting of overcurrent devices must not exceed the allowable ampacity of conductors that these o/c devices protect, the Rule further allows deviations from this requirement if the conditions of Table 13 are met, or if particular provisions for coordination between the allowable ampacity of conductors and the o/c devices protecting these conductors are governed by other rules of the Code.

In fact, these latter criteria could apply for General and Supplementary Sections. For instance, perfect examples of deviations from Rule 14-104 permitted by the Code are: Rules 26-208 and 26-210. These rules belong to another General Section (Section 26). But they govern installation of capacitors (of a very specific equipment that requires a unique coordination between the setting of the overcurrent devices and ampacity of conductors protected by these o/c devices), and as such these particular rules of Section 26 represent an exception to general provisions of Rule 14-104.

Other similar examples may be found in various supplementary sections (i.e., Rules 28-106 and 28-200 — for motors; Rule 62-114(7) and (8) — for space heating, etc.).

It is interesting to note that requirements of the installation Code (CEC, Part ) are also coordinated with provisions of the safety standards for electrical products (for electrical equipment, cables and wiring devices). In fact, each of these product standards states in its scope that the standard covers design and construction requirements of a specific type of electrical product that is intended to be installed in conformance with the CE Code, Part I.

No wonder that the installation Code is called the CEC, Part I, and each safety standard for an electrical product is called CSA Part II Standard.

So, this coordination perfectly demonstrates the fact that the safety requirements for design and construction of electrical products and installation rules represent two separate but complimentary parts of the single Canadian Electrical Code.

As it was mentioned above, the rules of the Code are correlated through the document to create a set of versatile and comprehensive requirements for safe electrical installations.

However, there are numerous relaxations from these rules in the body of the Code. These relaxations are manifested by notwithstanding clauses or statements such as "it shall be permitted”. These relaxing provisions are clearly linked to the specific conditions of installations, spelled in the rule. But there are also circumstances, where Code allows deviations from its prescriptive requirements based not on specific technical conditions, but rather on the fact that each such deviation may be obtained for the particular installation only from the authority that provides a regulatory enforcement of the installation.

Each situation where a deviation from the rules is deemed to be possible is conditional to provisions of Rule 2-030 "deviation of postponement”. Under this Rule, a designer (or an electrical contractor who obtained a permit for the electrical work) may approach the regulator with a request to deviate from a specific prescriptive requirement of the Code. Each such request must relate to a very particular installation (i.e., it must be unique, and not be used as a blanket approach), and it must be clearly substantiated that the relevant objective-based fundamental safety principles of the IEC 60364 (see above listed types of protection described by the IEC 60364) are fully met by that unique request.

Regulators evaluate each such request and may grant a special permission to deviate from the Code requirements for the particular installation.

However, the regulatory authority cannot grant a special permission for use of unapproved equipment. All equipment (except for provisions of Rule 16-222(2)) must be approved in order to be installed under rules of the CE Code, Part I. Code users should note that approved is the defined term, and this definition is clearly spelled out in the Code.

It should be also noted that the local regulatory authority must be consulted on a matter of deviations in every particular case of installation.

Read more by Ark Tsisserev

Tags:  Featured  March-April 2007 

Share |
PermalinkComments (0)
Page 57 of 111
 |<   <<   <  52  |  53  |  54  |  55  |  56  |  57  |  58  |  59  |  60  |  61  |  62  >   >>   >|