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Section 28 Motor Wiring Methods

Posted By Leslie Stoch, Saturday, September 01, 2007
Updated: Saturday, February 09, 2013

Motor wiring methods are covered in Rules 28-100 to 28-112 of the Canadian Electrical Code. Wiring up a motor may seem like a pretty simple job, but we still need to consider a surprising number of details for good compliance with the code. This article will review some of the more important CEC rules for conductor ampacities as applicable to motor type, insulation class and duty service.

Rule 28-104 refers to Table 37, which divides motor enclosures into two categories:

  • all motors except totally enclosed non-ventilated; and
  • totally enclosed non-ventilated motors.

For each motor enclosure type, Table 37 specifies the minimum wiring insulation temperature ratings applicable to motor insulation classes A, B, F and H. These letters identify motor insulation temperature ratings based on a 20,000-hour temperature test for each insulation class. The numbers under each motor insulation class identify the minimum conductor insulation ratings required for connection directly into a motor terminal box.

For example, a totally enclosed, fan-cooled Class B insulated motor requires a minimum 75ºC conductor temperature, while a totally enclosed, non-ventilated Class B insulated motor requires minimum 90ºC.

A note of caution—the wiring insulation data provided in Table 37 applies only for motors operating in an ambient temperature of up to 30ºC. If the ambient temperature exceeds 30ºC, the difference between 30ºC and the maximum air temperature must be added to the conductor insulation ratings given in Table 37. For example, a totally enclosed fan-cooled (TEFC) Class B motor operating in an ambient temperature of 40ºC must have a minimum conductor insulation of 85ºC.

The code also recognizes two separate duty service categories for motors. Each requires a somewhat different formula for selecting the motor wiring sizes. The categories are:

  • Continuous duty service—motors that are required to run continuously.
  • Non-continuous duty service—motors that may run for shorter periods of time and which are listed in Table 27 as to classification of service and running times.

Continuous Duty Service

Once the conductor temperature ratings have been determined, minimum wire sizes are selected from Tables 1 to 4. Rule 28-106 requires that motor conductors for continuous duty service motors be sized to at least 125% of motor full-load current. Reference to Table D16 helps to avoid all of that complicated math.

But another note of caution—motor conductor ampacities are not, as in the usual case, based on the allowable ampacities given in Tables 1 to 4, but rather on their 75ºC ampacities. It is important to note that in addition to the wiring insulation temperatures specified in Table 37, motor conductor sizes must be selected from the 75ºC column of Tables 1 to 4, which often results in larger wire sizes. Rule 28-104(1) provides an exception for Class A motors, to permit the 90ºC conductor ampacity.

Non-Continuous Duty Service

For non-continuous duty service motors, minimum conductor ampacities are specified in Rule 28-106 and Table 27 for the following duty service classifications:

  • Short time duty
  • Intermittent duty
  • Periodic duty
  • Varying duty

Table 27 specifies the minimum motor conductor ampacities as a percentage of full-load currents. As shown in Table 27, the minimum conductor ampacities are also based on the length of time during which the motors are expected to operate.

For example, the minimum conductor ampacity for an intermittent duty passenger elevator which may run for up to 15 minutes is 85% of the motor full load amperes. If on occasion that elevator motor must run for longer periods, the minimum conductor ampacity is increased to 140%.

Otherwise, the same conditions as for continuous service duty motors apply. After selection from Table 27, the minimum conductor temperature ratings must still be selected from Table 37 and their ampacities determined on the basis of their 75ºC insulation ratings. There may also be other reasons to increase wire sizes such as voltage drop.

As with previous articles, you should always check with your local electrical inspection authority for a more precise interpretation of any of the above, in each province or territory as applicable.

Read more by Leslie Stoch

Tags:  Canadian Code  September-October 2007 

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Has UL listed any CSST? Does UL list connectors to bond CSST?

Posted By Underwriters Laboratories, Saturday, September 01, 2007
Updated: Saturday, February 09, 2013

Question: Corrugated stainless steel tubing

I recently received a corrugated stainless steel tubing (CSST) manufacturer’s technical bulletin in the mail that I understand was mass mailed to a lot of electrical inspectors all around the country promoting the need to bond CSST due to lighting strikes. Has UL listed any CSST? Does UL list connectors to bond CSST?


As of this writing (June 2007), UL has not Listed any CSST or any grounding or bonding fittings intended for use on hexagonal shaped CSST fittings intended to bond CSST. Corrugated Stainless Steel Tubing (CSST) is a flexible corrugated tubing made of stainless steel with a polymeric jacket that is used in many areas of the country for distribution of natural gas. The technical bulletin in question recommends the use of a ground clamp secured around the hexagonal compression nuts on CSST fittings to bond the CSST gas piping system to the grounding electrode system.

UL Lists ground clamps under the product category Grounding and Bonding Equipment (KDER), located on page 172 in the 2007 White Book. Ground clamps are intended for use with ground rods and/or pipe electrodes in accordance with the NEC and are marked with the size of electrode and electrode grounding conductor with which the clamp is intended to be used. Clamps suitable for use on copper water tubing are marked ‘‘Copper Water Tubing,’’ or the equivalent, preceded or followed by the size of tubing. Ground rods, pipe electrodes and water tubing trade sizes are stated in fractions, such as 1/2, 5/8, etc. They have not been evaluated for use on hex nuts for CSST fittings.

If in the future, UL promulgates a Listing of bonding clamps for CSST, UL’s Regulatory Services Department will issue an email notification through its Ultimate Email notification system. If you aren’t currently an Ultimate Email subscriber and would like to be notified if a clamp for bonding of CSST is Listed, please logon to register for Ultimate Email and select gas and electrical as your interest areas.

Tags:  September-October 2007  UL Question Corner 

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Electric Shock Drowning

Posted By James D. Shafer, Sunday, July 01, 2007
Updated: Sunday, February 10, 2013

Yachts moored in a marina and connected to shore power present a unique electrical safety hazard which may be as lethal as the proverbial "hair dryer in-the-bathtub.” This review will explore the implications of this and what we have learned from investigating many in-the-water electrical accidents, a number of which have involved fatalities. The respected IAEI mentor Eustace Soares would have been intrigued by this unique lesson in the importance of grounding and bonding.

Photo 1. Houseboats moored at a marina

Electric Shock Drowning

Everyone was relaxing and enjoying the atmosphere at a party to welcome a new houseboat to the marina when the scene was suddenly shattered by the piercing screams of a young girl! The owner had given the girl permission to try out the new swim slide. She was in serious trouble from the moment she hit the water. One of the guests immediately jumped in to help—now there were two people in the water in great distress. The rescuer managed to push the girl to safety, and then disappeared below the surface—leaving a wife and two children.

Subsequent investigation disclosed that an ac "hot” lead in the lighting circuit developed a fault (insulation failure) to the metal hull, at a current level below the circuit-protection trip point, and something had happened to the green safety grounding wire. Thus, because this occurred in fresh water, the hull potential (voltage) went to some lethal level. It could have been as little as 25 VAC.

This became another incident of what we have termed electric shock drowning. We have catalogued over 100 similar accidents and this listing may be requested though the e-mail address at the end of this article.

Because fresh water is such a poor conductor, any fault that may occur in a boat’s wiring that is attempting to return to the source through the bonding system will cause a rise in potential on the hull or underwater gear if the bonding system to the dock is not intact.

As Soares Book on Grounding and Bonding points out, bolted faults rarely occur, so the integrity of the bonding conductor from the boat back to the source takes on a whole new importance in preventing a voltage rise on underwater hardware, since a breaker will usually not trip. While not easily confirmed it is suggested through many studies that as little as 2 v/ft gradient in the water can produce lethal conditions near a faulted boat. A person may feel a nasty shock at 2–3 ma through the body, but at 10 ma a child may become paralyzed and not be able to swim or stay on the surface — also referred to as let-go current (this 2 v/ft gradient will produce a 10-ma current in a nominal 1000-ohm person with a hand span of 5 ft). An electrician gets a broken arm from being knocked off a ladder because of the violent muscle reaction at these levels—but a swimmer will drown.

While the dock bonding system has only been implicated in a few accidents, the faulty wiring found on boats presents a real and more common problem. Because owners and nonqualified technicians do not understand the importance of a proper bonding system, work they undertake may totally ignore this essential element.

If the ABYC (American Boat and Yacht Council) Standard is followed, the ac and dc bonding systems on a boat are joined so that all metal components remain at the same potential. The NEC requires this also. Since salt water is a very good conductor, it will adequately substitute for a missing bonding connection to shore and lethal conditions will not occur around a faulted boat. Also, there is a greater likelihood that a circuit breaker will trip in this situation.

Fresh water is where the problem is—the "hair dryer in-the-bath tub.” Since current takes all paths back to the source, some water path current will always result from a fault to ground on the boat. Even a relatively low level current in fresh water will cause a high voltage gradient and cause lethal conditions near the boat if the bonding system is missing. In fresh water, the current split between a good bonding system and the water is about 95% (ground wire) to 5% (water path), and no dangerous water voltage gradient is produced. In salt water, the split may be more like 50 – 50, but nosignificant gradient will occur even with a defective or missing bonding system.

As inspectors, you may never get to see boats connected to shore power because your job is finished before the marina becomes operational. But on the occasion you happen to be in an operating marina, here is a test you might like to try.

Photo 2. Marina operators are in the best position to prevent accidents.

As stated, because current takes all paths even the smallest fault on a boat will cause some parallel water path current back to the source. If you clamp the shore cord with a good quality ac amp meter (two decimal places) this "missing” current will be displayed, and you have found a boat with a fault (note that GFCIs also work on detecting and acting on this missing current).

Do you get the feeling that there may be a lot of water path fault currents out there that people are not aware of? Your feeling is correct—and in the event of a defective bonding connection, in fresh water, the stage is set for a fatal accident. A one-page procedure for this test is available from us, and it outlines some important considerations for the above test.

Since GFCIs are not now required on the marina 30-A and 50-A locking-type receptacles, we have developed a system for locating boats with low-level faults, and the system is on duty 24 hours a day. Our Marina Guard® ground-fault monitor may be located near the service, or at any new derived point, and will alert marina personnel if there is any fault either in the dock wiring or on a boat above a preset trip level. As a result of a proposal made to the NFPA-303 committee two years ago, ground-fault monitoring has become a part of this standard in the 2006 edition. This was a major step forward to help prevent these rather unique and tragic marina accidents.

The monitor alarm levels are set, at this time, based on the marina and ambient current both on the docks and the connected boats. As repairs are made to these systems, the leakage current trip levels can be set low enough to provide a warning below the danger level. Since the dock wiring and the associated group of boats monitored (as many as 20 – 30) will have some combined ambient leakage, alarm set levels cannot be specified at the initial installation.

We think the next step may be some kind of ground-fault protection (GFP) device at the main electrical panel disconnect on the boat or at the dock-pedestal receptacle breaker. The USCG has provided us with a grant to study this problem and to make a recommendation to improve electrical safety in the marina environment. One aspect of our study is aimed at determining what trip level would be suitable for a GFP, taking all the factors into account. This year-long study is currently underway—information on this may be requested.

While the 5-ma GFCI level has become the standard for most applications, it is our opinion at this time that the trip current setting of a GFP could be a good deal higher and still provide swimmer protection because of the uniqueness of the situation. The problem with the 5-ma GFCI is it may be subject to nuisance tripping (a bad word, I know) and is therefore only infrequently found in marinas. A GFP level which will not cause false tripping and yet provide a safe level of protection for any one who is in the water is what our study is to determine.

Most of our efforts are directed toward educating marina operators because they are on the front line every day and are in the best position to prevent accidents. To address this need, we have developed a half-day electrical safety seminar for non-technical marina staff, and it has been very well received. Of all the things we have done to solve this problem, this probably has been the most effective.

We appreciate this opportunity to bring our message to IAEI. We need the support of highly trained professionals like you who understand the problem.

A number of articles are available on request and information on the Marina Guard® may be found on our website We welcome your questions and comments, so please do not hesitate to contact us.

Read more by James D. Shafer

Tags:  Featured  July-August 2007 

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Calculated Demand and Underground Ampacities

Posted By Robert Edwards, Sunday, July 01, 2007
Updated: Sunday, February 10, 2013


The main thrust of this article is to establish that Section 8 of the Canadian Electrical Code Part I does not have adequate rules to address derating factors for continuous loads, or to calculate the minimum ampacity requirements for the safe sizing of conductors and electrical equipment, when the underground ampacity calculation is performed to size conductors, and to propose how solutions to these issues should be developed. The current derating factors for continuous loads apply strictly to installations above ground.

It is shown that the continuous load derating factors in circuits installed underground, and the correction factors to be applied to the calculated demand to obtain the minimum required ampacity, can only be derived from derating factors currently in Section 8. However, their application is not intuitively clear and lead to increased complexity compared to circuits installed above ground. Accordingly, the proposals for accommodation of new rules applicable to continuous loads in underground installations need to be simplified as far as possible. The application of appropriate correction factors to the calculated demand is recommended to this end, in place of the more obscure format of derating factors applied to the ampacity, which presently exist for installations above ground.


Most code users are generally familiar with the provisions of Section 8, which addresses circuit loading and demand factors. In general terms the rules provide a means of properly sizing conductors and electrical equipment so that they will adequately and safely support the anticipated load currents demanded of the circuits of electrical installations, whether in consumer services, feeders, or branch circuits.

The purpose of most of the rules from 8-200 onward relate to the calculation of the expected electrical loads based on a number of defined attributes of the premises. They include such attributes as their area, the type of use and occupancy, and the types of electrical load anticipated on those premises. Having estimated these load currents by calculation as provided for in the 8-200 to 8-400 series rules, the calculated loads are then used in turn for the sizing of conductors and equipment in each of the circuits.

Rules for the sizing of conductors are contained mostly in Section 4 of the Code, with some further applicable rules appearing in Section 12. However, the provisions of Rule 8-104 must also be observed, and this rule plays an important role in the safe and proper sizing of conductors and electrical equipment. Rule 8-104 has been around for several code cycles in various incarnations, and its provisions merit some in-depth scrutiny to examine whether it continues to meet the needs of code users and regulators.

Rule 8-104

If the purpose of Section 8 is to determine the required circuit ampacity as a basis for establishing the appropriate conductor sizes and equipment ratings for the circuits of the installation, Rule 8-104 has to be examined thoroughly to find any clues as to how this goal is furthered. The title Maximum Circuit Loading suggests limitations or constraints on the loading of the circuits rather than a basis to choose conductor sizes and equipment ratings. In fact, Rule 8-106 appears to give the appropriate signal as to how to obtain conductor sizing, particularly subrule (6). The maximum circuit loading theme is picked up in subrules (4) and (5) of 8-104. In both subrules the key phrase "….the continuous load…..shall not exceed (some prescribed percentage of) the rating of the circuit…” is employed. We can conclude that one major reason for subrules (4) and (5) to exist is to limit the continuous load on the circuit, based upon its ampere rating.

The basis for limiting the continuous load is found in CSA and UL standards for certain common types of electrical equipment, which are described in the first few words of subrules (4) and (5). The product standards provide for equipment to be marked either as suitable to carry 100% or its nameplate rating, or, more commonly, as suitable to carry 80% of its nameplate rating. In order to prevent the overheating of electrical equipment marked as suitable to carry 80% of its nameplate rating, the equipment is required to be derated. When the conductor size is determined in accordance with Tables 2 or 4 of the code (for wiring in raceways, or multiple conductor cables) the continuous current is limited to 80% of the circuit ampere rating. In the case of conductors selected from Tables 1 or 3 of the code (for single conductors in free air), the applicable derating factor is 70%. A derating factor of 85% is also applicable to equipment marked as suitable to carry 100% of its nameplate rating when conductors are chosen from Tables 1 or 3.

Influence of Conductor Size on Electrical Equipment

The application of the specified derating factor is essential to avoid the overheating of the electrical equipment. The conductors are derated along with the equipment, not because the conductors cannot carry the continuous load without overheating in their installed location (which they can), but because the selection of the smaller conductor sizes which are permissible for non-continuous loads would potentially contribute to equipment overheating. Smaller conductors simply cannot conduct heat away from the terminals of the equipment as efficiently. For many years there was no special consideration given to the sizing of equipment in the case of conductors rated according to the single conductor free air ratings of Tables 1 and 3. Rule 8-104 only used to make provision for a derating to 80% of the circuit ampere rating, no matter which tables were used as a basis for conductor selection. The growing application of the single conductor free air ampacities raised concerns that the smaller conductors permitted in Tables 1 and 3, compared with Tables 2 and 4, might give rise to a greater incidence of equipment overheating, particularly in the case of continuous loads. In the 1970s a manufacturers’ task group, with representation from the electrical equipment and wire and cable manufacturers, recommended the derating factors which are present today in subrules (4) and (5). The higher derating factors to be applied when conductors are sized in accordance with the free air ratings of Tables 1 and 3 were supported by test programs carried out by electrical equipment manufacturers.

Continuous and Non-Continuous Loads

Note that subrules (4) and (5) only apply in the case of continuous loads. The case of non-continuous loads is adequately provided for in subrule (2). The question is, how do we differentiate between continuous and non-continuous loads? The best answer to this is found in subrule (3). The adjective "best” is used because subrule (3) provides a practical "rule of thumb,” rather than a precise means of differentiation. In practice, equipment can be installed in a wide variety of possible locations, with different rates of heating and cooling depending on a wide range of factors. These factors include those such as physical dimensions, proximity of other heating and cooling sources, loading factors, and many others besides. Consequently, there is a wide variety of possibilities of the temperatures on the equipment terminals, but only two options are available for the decision as to whether the load is continuous or non-continuous, as outlined in subrule (3)(a) and(b). [See also Rule 8-302(2)]. In addition, the onus of proof for the decision as to whether the load is continuous or non-continuous generally rests with the installer or designer, although some authorities having jurisdiction take this decision out of their hands by declaring that all loads are to be considered continuous. In some "rough and ready” way, subrule (3) provides a means to differentiate between what is considered to be a continuous load, and one which is not. By the wording of the different criteria [either (3)(a) or (3)(b)], there is also some recognition that equipment of lesser ampere rating, and therefore of generally lesser physical bulk, will achieve its steady state temperature more quickly than equipment of higher ampere rating, and greater bulk.

A further observation is pertinent to the issue of continuous and non-continuous loads. The "rule of thumb” of subrule (3) has been around in the Code for many years, and precedes the inclusion of underground ampacities in Section 4. In an underground environment, the time for the conductors to reach a steady state temperature will take far longer than the period of 6 hours, which is the longest period mentioned in subrule (3). When conductors are run underground, whether directly buried or in raceways, the ultimate steady state temperature of the hottest conductor underground will not be achieved within a matter of hours, rather of days, perhaps even many days in the case of high ampacity circuits with many conductors connected in parallel. (A more detailed discussion of this point is provided separately elsewhere). It is clear that subrule (3) is inadequate to describe the characteristics of the conductors installed in the greater (underground) part of the circuit. Of course, the ends of these conductors are connected to the equipment outside of the underground portion of the conductors, because the equipment is installed almost invariably in air, even though the conductors may run underground for much the greater part of their length. For this reason, installations run underground may still quite properly be addressed by the criteria of subrule (3), even if the steady state conductor temperatures in the underground portion of the circuit take much longer to achieve their steady state temperature than does the electrical equipment connected at their ends.

Determination of Circuit Ampacity

We still have to address the question of how the Section 8 rules provide for the progression from the calculated demand to the required ampacity and equipment rating. Subrules (4) and (5) are designed primarily, as we have just seen, to limit the temperature of connections on electrical equipment to safe levels through the use of derating factors. How does this help with the sizing of conductors and equipment? There is perhaps a clue in the use of the phrase "…….the continuous load as determined from the calculated load” in both subrules (4) and (5). The phrase may be considered as ambiguous upon first reading, in fact. It does not say how the continuous load is to be determined from the calculated load. What the wording in italic print is intended to mean is "….the continuous load which for, the purpose of this rule, is to be read as the calculated demand load……” In practice, this phrase actually intends to equate the maximum permitted continuous load with the calculated load, and therefore creates a tie to the circuit ampacity through the derating factors specified. Neither subrule, in fact, explicitly tells the code user to calculate the circuit ampacity from the calculated demand and the derating factors. However, it is implicit, provided that it is agreed that the continuous load mentioned in subrules (4) and (5) is the calculated load. Most code users have learned to apply the derating factors of subrules (4) and (5) inversely, correcting from percentage values to per unit values. For example, a derating factor of 80% would equate to a per unit factor of 0.80, used as a divisor to the calculated demand load to determine the ampacity. This would require a calculation to divide the calculated demand load by 0.80, which is the same as multiplying by 1.25. This is logical, if a little convoluted. It does raise the question, however, as to whether a subrule intended primarily as a means of preventing equipment overheating is the best vehicle for the determination of ampacity from the calculated demand load. Why does such an important calculation not deserve explicit rules of its own?

In retrospect, it is considered that the rules related to limiting the continuous current on electrical equipment for safety reasons would be better separated from the rules related to the determination of minimum required ampere rating from the calculated demand. It can even be argued that, if the code had satisfactory rules to determine the required circuit ampacity from the calculated demand, the necessity to consider what the maximum circuit loading should be would become a redundant exercise. If, in the example given in the previous paragraph, the rules were rewritten to say something such as "Multiply the calculated demand by 1.25 to obtain the minimum required circuit ampere rating,” the step from the calculated demand to the ampere rating of the circuit would be clear. The need to consider what the maximum circuit loading should be also becomes redundant, since the rules would provide the correct ampacity, and the equipment would be automatically protected from overheating without the need to address it. The need for a "determination of minimum circuit rating” rule, instead of a "maximum circuit loading” rule, becomes clearer in considering the particular circumstances associated with underground ampacities and the determination of the appropriate derating factors and correction factors to be applied.

Derating Factors When Conductors Are Installed Underground

A further look at Rule 8-104 brings out a point which is even more important, in that there is a serious deficiency concerning the requirements for conductors sized to underground ampacities. Several years ago, when Rules 4-004(1)(d) and (2)(d) were added to the Code to better accommodate ampacities of conductors installed underground, a further subrule was added to Rule 8-104 in recognition of the possible effects of the conductor sizing on equipment overheating. [See 8-104 subrule (7)]. Calculated underground ampacities can yield conductor sizes which are smaller even than those provided in Tables 1 and 3 for single conductors in free air in some cases. Subrule (7) was added to ensure that conductors used in underground installations cannot in any case be smaller than would be obtained from Tables 1 and 3 for the same ampacity, particularly in the case of continuous loads. However, for conductors sized according to Tables 1 and 3, a derating factor is required according to subrules (4)(b) and (5)(b). As we have seen, this would lead to an increase in the required ampacity and conductor size for continuous loads. How does Rule 8-104 address derating factors for conductor sizes calculated from underground ampacity rules of Section 4? Are derating factors required, or not required, when conductors are sized according to Rules 4-004(1)(d) and (2)(d)? Scrutiny of 8-104(4) and (5) shows that the rules are silent on this issue. Rule 8-104 subrules (4) and (5) only apply to cases when the conductors are installed above ground, whether according to Tables 1 and 3 (for single conductors in free air) or according to Tables 2 and 4 (for wiring in raceways or multiple conductor cables). Not in Rule 8-104, nor anywhere else in the code, are derating factors required when the conductors are sized according to the calculated underground ampacities. This is a serious omission which needs correction. In fact some code users and regulators may sometimes intuitively turn to established derating factors intended for conductors installed above ground, commonly 80%, even without code rules for underground circuits to justify this. However, it will be shown that the technically correct choice may not be readily apparent, and some thought needs to be applied in order to obtain the correct derating factor when conductors are installed underground.

From the point of view of the equipment, the terminals do not "know” whether the conductors connected to them are installed underground or above ground outside the equipment. Common sense dictates that the equipment should be protected from overheating in equal fashion, whether the conductors run underground, or above ground outside the equipment. We have seen, however, that we apply different derating factors for single conductor free air installations than we do for conductors installed in raceways above ground. For conductors installed underground, would the derating factors for single conductor ratings or those for conductors in raceways be the most appropriate choice? Or should there be a separate set of derating factors when the conductor sizes are based on the underground ampacity calculation?

Development of Derating Factors for Underground Installations

It has been shown elsewhere the calculated ampacity of an underground circuit conductor can be significantly different than the ampacity of the same conductor run in free air, and than that run in a raceway above ground. In lower ampacity circuits, the calculated underground ampacity may be considerably higher than that of the same conductor run in raceways above ground, and even exceed the free air ampacity of that same conductor. However, in higher ampacity circuits, the calculated ampacity of the underground conductor may be lower even than the ampacity of that same conductor run in raceways above ground. In circuits of intermediate ampacity, the calculated underground ampacity of the conductor will usually fall between the single conductor free air value and the value of that same conductor run in a raceway above ground. Various cases will be considered for the determination of which derating factor is most appropriate, when the load is continuous. For explanatory purposes, only the case of copper conductors connected to electrical equipment marked as suitable to carry 80% of its nameplate ampere rating will be considered.
The following notes refer to figure 1.

Note 1. When the conductor size calculated from underground ampacity rules equals that provided in Table 2
Given that the equipment is connected to the same size conductor, whether the conductors run above ground in a raceway or below ground, it stands to reason that the derating factor to be applied to the continuous load should be the same in either case, i.e., 80%. Conversely, a correction factor of 1.25 should be applied to the calculated demand load in order to determine the appropriate minimum circuit ampacity.

Note 2. When the conductor size calculated from underground ampacity rules equals that provided in Table 1
By similar reasoning to Note 1, the derating factor to be applied to the continuous load should be the same in either case, i.e., 70%. Conversely, a correction factor of 1.43 should be applied to the calculated demand load in order to determine the appropriate minimum circuit ampacity.

Note 3. When the conductor size calculated from underground ampacity rules lies between the sizes obtained from Table 1 and Table 2

If the calculated load according to Section 8 rules leads to a conductor size in this range, i.e., smaller than that provided by Table 2, but larger than that provided by Table 1, a derating factor of 80% would not be appropriate, as it would not protect the equipment adequately. The smaller underground conductor size than that obtained from Table 2 translates into poorer heat dissipation from the terminals of the equipment, and higher terminal temperatures. Clearly the risk of overheated terminals would exist, although less severe than the degree of overheating which would result from choosing the even smaller conductors which would be obtained from Table 1. Logically, there would be a theoretical derating factor somewhere between 70% and 80% which would be safe for any particular calculated load, but there is no way of knowing what that value would be without extensive testing. In the absence of any other appropriate derating factors to be applied to the continuous load, other than 80% or 70%, the 70% value must be used, even though it would be conservative in many cases. Conversely, a correction factor of 1.43 would be appropriate to apply to the calculated demand load in order to determine the appropriate minimum circuit ampacity.

Note 4. When the conductor size calculated from underground ampacity rules is smaller than that obtained from Table 1
It has already been shown that the effect of 8-104(7) is to limit the ampacity of conductors installed underground so that they cannot exceed the free air ampacity, in this case, of Table 1. The appropriate derating factor is the same as in the case of item 2, i.e., 70%, since the Table 1 ampacity overrules the calculated underground ampacity. Applied to the continuous load, the 70% derating would ensure safety from overheating. Conversely, a correction factor of 1.43 would be appropriate to apply to the calculated demand load in order to determine the appropriate minimum circuit ampacity.

Note 5. When the conductor size calculated from underground ampacity rules is larger than that obtained from Table 2
The larger conductors would lead to more efficient heat dissipation at the equipment terminals than the conductors selected from Table 2, and this is clearly a safer condition than in the case of Note 1. Such a condition would be similar to the case of oversized conductors required from voltage drop considerations. It would also be expected that the equipment would run cooler than would be the case under certification testing, in which the conductors are effectively the same sizes as in provided in Table 2. A derating factor of 80% applied to the continuous load would be appropriate to ensure safety from overheating. Conversely, a correction factor of 1.25 would be appropriate to apply to the calculated demand load in order to determine the appropriate minimum circuit ampacity.

Note 6. When the conductor size calculated from underground ampacity rules is as large or larger than obtained from Table 2, when the calculated demand is increased by 125%

A special case exists of that described in Note 5 when the calculated underground ampacity is less than 80% of the Table 2 ampacity of the same conductor. In that case, the conductor size is clearly adequate without any derating to the underground ampacity, for the conductor is as large or larger than would be the case of the choice from Table 2 even after the application of a 125% factor to the calculated demand. The conductor size would be as large or larger than would apply for certification testing, and would therefore be considered safe. On the other hand, the equipment would still require to be derated to 80% of its rating, for this is also the test current for certification testing. In this case, a factor of 125% would be applied to the calculated demand in order to give the minimum equipment rating, but the conductors could safely be sized with an underground ampacity of 100% of the calculated demand.

Although in the examples chosen, we have considered only copper conductors and electrical equipment marked as rated to carry only 80% of its nameplate ampere rating continuously, it is considered a simple task to extend the logic of items 1 to 5 above to those installations having aluminum conductors, and to equipment marked as rated to carry 100% of its nameplate ampere rating continuously.

It is beyond the purpose of this discussion to propose new code rules to address the points that have been raised. This is the prerogative of the Part I Committee and the Section 8 Subcommittee. It is hoped that the nature of the perceived deficiencies of the Part 1 rules in addressing derating factors, and the required factors to obtain the minimum circuit ampacity from the calculated demand, are better understood. It is expected that the rules addressing the needs of deratings and determination of ampacities may turn out to be more complex in their wording than the wording of the existing 8-104 subrules (4) and (5). This is because the determination of conductor size according to underground ampacity rules leads inevitably to a comparison against what the conductor size would be if the same conductors were to be installed in free air, and if they were to be installed in a raceway above ground. Only then can the appropriate derating factor and factor appropriate to determine the circuit ampacity from the calculated demand be established.

A significant part of this exercise is expected to be the development of a flow chart, intended to be located in Appendix B, associated with rule 8-104. The flow chart will complement the code rules and provide a step-by-step basis to work through the natural progression from the calculated demand to the minimum circuit ampacity. The flow chart has been under development for some time. Because the determination of the minimum ampacity from the calculated load in underground installations is tied closely to the method required for single conductors in free air, and conductors installed in raceways above ground, each of these conditions is included in the flow chart. It should be understood that the flow chart does not apply under current code rules in Section 8, but under Section 8 rules which still require development.

Read more by Robert Edwards

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Summer Camping Electrical Safety

Posted By Bruce A. Hopkins, Sunday, July 01, 2007
Updated: Sunday, February 10, 2013

As the season of sun comes upon us, many folks will be planning their summer vacations. To enjoy the freedom of adventure and flexibility, camping is the perfect family getaway. Whether one is using a folding camping trailer, a full-sized motor home or any of the many other models of recreational vehicles (RV), fun is the key motivator. However, as with anything, safety is a primary concern and needs to be investigated to ensure that fun is the memory of the summer.

First, check all power supply cords

When camping with an RV, be sure to pay attention to electrical safety basics. Most RVs have a 120-volt ac electrical system that allows the conveniences of home to be with you. TVs, radios, electrical frying pans, coffee pots and a host of other devices can be safely used within the RV. A power supply cord is required by the National Electrical Code to be of sufficient length to connect the RV to the power supply at the campground. Sometimes, the space between the RV and the power pedestal is greater than the power cord permits and an extension cord is needed to make the connection. Various considerations need to be evaluated when using an extension cord. Be sure the extension cord is of sufficient size to handle the load demanded by the RV. If the power cord of the RV is rated 30 amperes, the extension cord also needs to be rated for at least 30 amperes. Such extension cords are more expensive, but well worth their cost. Typical extension cords used in the home are not rated for exterior use and do not have wires of sufficient size to carry the load. This can lead to under powering appliances and devices, or, of greater concern, the wires may become overheated leading to a potential fire.

Second, use only cords with the third pin

Also, be sure the third pin on the extension cord has not been removed. The removal of the ground pin could allow the plug to be inserted improperly, leading to reversed polarity. If another fault is present in the system, such as a loose wire, the combination could be fatal as the entire exterior skin of the RV could be come energized. Touching the energized exterior of the skin could cause electrocution. A correctly wired RV, using the proper extension cord with an intact ground pin will provide safe and enjoyable usage.

Third, ensure all GFCIs are working properly

Another safety tip that can e-liminate potential issues is to check the ground-fault circuit-interruption (GFCI) protection devices that are installed in all RVs on receptacles that are close to sinks, lavatories, and shower/bathtubs. The GFCI device is designed to "trip” in the event a leakage out of the circuit is more that 5 milliamperes. If the leakage is greater than the 5 milliamperes, the device will turn itself off. A special receptacle or circuit breaker can be identified as a GFCI device by the presence of a test and reset button on the receptacle, or a test button on the circuit breaker. You should push the test button to be sure these devices are in working order. Once the device is off, no power should be at that receptacle or at any other receptacle that is downstream and on the same circuit. Push the test button, plug a hand-held device, such as a hair dryer, into the receptacle and turn it on. If the hair dryer does not work, reset the circuit breaker by flipping the handle back to the on position or pushing the reset button on the receptacle. If the hair dryer works again, the GFCI is working.

The proper use of extension cords and ensuring the GFCI devices in the RV are working correctly can ensure the safe fun time you are expecting on your vacation. The easy steps outlined herein will preserve your fun vacation and leave you with fond memories.

Read more by Bruce A. Hopkins

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Illegal Multi-Family Dwelling

Posted By Bart Archibald, Sunday, July 01, 2007
Updated: Sunday, February 10, 2013

Connecticut had experienced unseasonably warm weather for the months of November, December and January, with days reaching into the sixties, but by February, winter had returned with a vengeance with nighttime temperatures declining into the minus six degrees range.

On the night of February 20th, as I was just finishing an evening walk, my cell phone rang. It was Brian Donovan, my supervisor and the building official for the town of Stratford. He asked if I were on the couch keeping my feet warm. When I replied that I was not, he requested that I respond to a call he had just received from fire dispatch regarding a broken pipe. Water from the pipe was flowing from a first floor apartment into electrical equipment that was installed in the basement. As part of our duties as town inspectors, Brian and I are on-call 24/7. We alternate responding to emergencies that are related to structures and/or equipment that is damaged and regulated by the code, such as structural failures, fires, automobiles hitting buildings, storms and wave damage, natural gas leaks, water damaged electrical equipment, etc.

Photo 1. The author posts a notice alerting anyone entering the basement area of the potential shock and fire hazard due to water-soaked electrical equipment and conductors.

Photo 2. The lampholder and switch were outside the entrance to the basement apartment; notice that there are no boxes for either. Conductor is a lamp cord, with cord and terminal exposed to contact and physical damage. Both are attached to the door trim

When I reached the site, a fire truck, with its lights flashing, was parked in front of a two-story house. Hanging from a pole in the front yard was a real estate sign that read, "Multi-family Residence FOR SALE.” As I approached the fire truck, the driver behind the wheel recognized me and said that the lieutenant was "around back.” At the back door was the real estate agent who had called the fire department after discovering the broken pipe, as well as the lieutenant and two additional firefighters.

The lieutenant explained that the agent had come by to check on the house because the owner was on vacation in Brazil. Apparently, before leaving the country, the owner had lowered the thermostats in three apartments. The first floor heating pipes had "let go,” and the water had covered most of that level before leaking into the basement. The pipe had probably broken during the extremely cold weather last night or earlier in the week. Now that the weather had warmed up, any pipes that had frozen and broken during the cold spell, would start running water. That is what occurred here.


Photo 3. This luminaire (lampholder) is installed in a clothes closet [NEC 314.17(A) & (B), 410.8(C)

As I followed the lieutenant down the stairway to the basement, he warned me to watch my head, since the headroom was about five feet, five inches and one of his men had already hit his head.


The water main had already been turned off. There were three electrical panels in the basement. Since the lieutenant could not isolate the particular circuits to the affected areas, the main breakers had been opened to avert a potential fire and shock hazard.
I followed the flow of water that was dripping from the ceiling into the light fixtures and down the wall and into the electrical wiring and outlets. From there the water went into a sump pump that had kept the basement from filling up with water. Without a sump pump, it is common for a cellar to fill up with water when a broken pipe goes undetected

Opening a door at the bottom of the stairs, we entered a kitchen via a corridor, which connected to a bathroom and three bedrooms. There was no other means of egress! All the windows in the bedrooms where six feet above the floor and very tiny—about twelve inches high by twenty inches wide. I thought to myself that in an emergency, if the one exit were blocked, no one would be able to escape though these windows. Without a second means of egress, a person’s chances of getting out of the basement were slim.

No smoke detectors, sprinklers or fire alarm systems where installed. I mentally noted that without an early warning system, the possibility of survival in a fire became very doubtful. There were also signs indicating that this basement apartment had recently been constructed. By now, I began to suspect that it was highly unlikely that any inspections, permits, or certificate of occupancy had been issued. This property was an illegal multi- family dwelling.

Photo 4. Only one of the three basement kitchen counter-top receptacles is installed in a box; note the length of Romex in box. Coming out from underneath the cover was a lamp cord that fed the downstream receptacle and attached to the top of the back spl

I questioned the agent about the number of apartments, and whether they were occupied at this time. The agent stated that the vacationing owner lived in the first-floor apartment. Because the house was for sale, the second-floor and basement apartments were empty. A female tenant, who was not at home at this time, occupied the third-floor apartment. I explained to the agent that unsafe conditions existed due to the lack of exits, as well as the fact that the electricity and water had been turned off. I stated that the building is currently in violation of the Connecticut General Statutes and would remain so until the following occurred: (1) She needed to contact the owner, or some other person authorized to hire a plumber and electrician, both for emergency repairs and to abate the unsafe conditions and violations; (2) the necessary permits and inspections would also have to be obtained and a certificate of occupancy issued. Since it was getting late and the house was extremely cold, I decided to return in the morning when there was more light.

Just as we were preparing to leave, the third-floor tenant drove up. The agent tried to explain to the young woman what had happened and why she could not currently live in her apartment. The tenant told us she was from Brazil and understood very little English, due to being in this country for only a short time. She comprehended the basics, however, and told us that she had been visiting with relatives and could stay with them for a few nights. When she asked if it would be OK to get some clothes from upstairs, I used my flashlight and accompanied her to the third floor apartment, via the rear stairs. This apartment, which had sloping ceilings, consisted of a kitchen–living room combination, a bathroom, and two bedrooms. There were no emergency and/or rescue-size windows, nor a second exit.


Photo 5. Receptacle (installed in sheet rock) terminal is touching the insulation paper that reads, "warning this paper will burn. [NEC 110.3 (B), 110.8, 110.18, 240.5, 250.4, 300.15, 314.16, 314.17(A), 400.8, 402.11

The next morning arrived with bright sunshine and warmer temperatures. I searched through the building department files, looking for any permit for the address. As I expected, none had been issued. I contacted Deputy Fire Marshall, Brian Lampart, and the real estate agent. We all agreed to meet at 10:30 a.m. to continue my inspection. In addition, because this was a four-family dwelling, the fire marshall had jurisdiction. Before leaving the office, I contacted Ron O’Malley from the engineering department and asked if he were available during lunchtime to join us with his camera to take some pictures of the electrical violations. I knew that without visual proof, the violations would not be believable. In keeping with the saying, "A picture is worth a thousand words,” this article will be thousands of words shorter because of pictures.
As our group made our way though the rooms in the basement and then the third floor taking photos, documenting violations, and discussing the conditions, Brian and I knew we had a long afternoon ahead of us writing the applicable notices and reports.


In Connecticut, Section 115 of the code requires that if an unsafe condition is found, the building official shall serve on the owner/agent of the person in control of the structure, a written notice which includes the following: (1) a description of the conditions deemed unsafe; (2) a specification of the required repairs or improvements to be made to abate the unsafe conditions; and (3) a statement of the requirement that an unsafe structure is to be demolished within a stipulated time. Section 113 states in part that "it shall be unlawful for any person, firm or corporation to erect, construct, alter, extend, repair, move, remove, demolish or occupy any building, structure or equipment regulated by this code, or cause same to be done, in conflict with, or in violation of, any of the provisions of this code. Such order shall direct the discontinuance of the illegal action or condition and abatement of the violation.” After completing the notice of unsafe conditions and violations, I mailed the owner a certified original with return receipt, filed the copies, and returned to my assigned tasks.

Three weeks passed before the owner came into my office. He had the orders in hand and a proposal that would abate the illegal four-family dwelling to its original two-family residence status, with the addition of a habitable attic that would communicate with the second floor apartment. The basement would be converted back to its original storage use. After reviewing the plans, I issued the appropriate permits.

I am happy to report that an inspection was performed yesterday, and the work is proceeding as planned. The necessary repairs to abate the documented violations and unsafe conditions are very close to being completed. After finishing the inspection, the owner and I walked outside, discussing a few additional alterations he had been planning. He thanked me for taking the time to explain the ways to make his plans code-compliant. The owner then commented that being an inspector seemed like a thankless job, and asked me, with my experience and knowledge in the building industry, why I would choose being a building inspector as a profession.

In a flashback, I remembered that I had pondered this question many times when first starting as a building official in another town. I especially remembered one of these occasions. I had just performed a certificate of occupancy inspection on a two-story addition, with a couple of bedrooms for a growing family. The contractor had neglected to install a smoke detector in one of the bedrooms. When I informed the homeowner that she was required to have a smoke detector installed in all the bedrooms before I could issue the certificate of occupancy, she became very agitated, giving me "the look” of total disgust, that is so familiar to all inspectors. She wanted to know why an additional smoke detector was required when there were smoke detectors in all other parts of the house. I explained to her that, according to Connecticut code, when a new bedroom is added, smoke detectors are required in each bedroom. When leaving, I asked myself if this job were worth the aggravation.

Then, a few days after the New Year, I responded to a house fire that claimed the lives of two small children and a father. One child who died was not a family member but had been sleeping over. Of all the possible reasons they did not get out in time, a significant one was that there had been no working smoke detectors in the home. Thinking about the children being carried out, changed me forever. That night on the way home, I purchased two boxes of smoke detectors, stopped by the homes of all my friends and family members who had children, and installed smoke detectors in their rooms. Each one of my grandchildren also has a smoke detector that they take with them when sleeping over at a friend’s house.

About two weeks after the tragic house fire, I was called back to do a re-inspection at the house of the woman who had been so upset with me. When she answered the door, she immediately apologized for her behavior on the previous inspection, saying she had read in the newspaper about the children dying in that house fire, and told me that she respected my insistence on having all the detectors in place before I issued the C.O. Walking out of the house that day, I had a feeling of total satisfaction of a job well-done.

To respond to the man’s question regarding why I chose being a building inspector as a profession, I simply stated that if one person’s life is saved, then I have done my job, and that is thanks enough for me!

Read more by Bart Archibald

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A Swimming Pool Is Just a Big Bathtub, Isn’t It?

Posted By Jim Maldonado, Sunday, July 01, 2007
Updated: Sunday, February 10, 2013

The answer to this question is yes and no. That sounds like an answer from an inspector, doesn’t it? Yes, it is just a large container of water, but when you mix electrical equipment, such as pumps, heaters, and lighting with this large container of water, there can be problems. Article 680 addresses "…all swimming, wading, therapeutic, and decorative pools; fountains; hot tubs; spas; and hydromassage bathtubs, whether permanently installed or storable…” (680.1 Scope).

Pools are pools, why keep changing the Code?

Photo 1. Typical forming shells used for underwater lighting being bonded to the equipotential bonding grid. Ground clamp used in this fashion needs to be listed for direct burial.

I have been around the construction business my whole life, beginning as the son of a general contractor, then as a journeyman electrician, and for the last twenty years as an inspector and a plan check engineer. During this time, I have observed many changes within the industry. New methods and materials are continually being developed and used in all types of construction.

The construction of swimming pools is no different. Most people understand the obvious dangers involved with a swimming pool. In the Phoenix metro area, there were around 52 fatal drowning incidents in residential backyard pools this past year. Fire Departments continue to preach the need for pool fencing and other safety measures to keep small children away from pools and for adults to supervise children around pools. Most cities have adopted very strict pool fencing ordinances that require fences, self-closing gates and doors, alarms on doors and windows or pool covers. Of all the public service announcements on pool safety every year, I have yet to hear one that addresses electrical safety. Most pool owners take it for granted that their pool is safe from electrical hazards. I imagine they are not concerned about their pool’s safety, since there are not as many newspaper articles that document deaths or injuries directly attributed to electrical problems. I would like to think that the low numbers of these accidents are because of the electrical installation requirements of theNECand good inspection practices.

In this article, we will discuss some new materials and practices currently being used for pool construction. How do we keep up with all of these changes and make sure that the pools we inspect are electrically safe? First, we need to keep up on Code changes by attending code update classes conducted by IAEI. Second, we also need to adopt the most current edition of theNECavailable; and, third, we need an understanding of the problems related to electrical hazards around pools. In the 2005NECamendment process, there was a rewrite of the bonding requirements for pools in NEC 680.26, but even with our best efforts, the re-write was hard to understand, so a tentative interim amendment (TIA) was issued to clarify the requirements of this section. If you have adoptedNEC-2005, you need to get a copy of NFPA 70, TIA 05-2 to understand this section clearly. InNEC-2008, the language was tweaked even further to address additional testing data and to zero in on the whole intent of this section.

How are pools different today?

Photo 2. Gunnite (concrete) permanently installed pool with concrete deck using bare structural steel reinforcing embedded within the concrete. The belly and deck steel will serve as the equipotential bonding grid.

When I first started as electrician about thirty years ago, pools were built pretty much the same way. Usually, they consisted of gunnite (concrete) walls, concrete Kool Deck that used bare structural steel reinforcing embedded within the concrete. The reinforcing steel usually consisted of #3 (3/8″) rebars spaced at 12″ on center, both horizontally and vertically, around the shell of the pool and extended from the pool wall into the deck surface. They usually had a filter, chlorination system, and lights with metal light niches; sometimes they included a gas heater, diving board or a slide.

Pools are now being designed and built for salt-water use or with salt-based chlorination systems, which can corrode the bare reinforcing steel embedded within the concrete. Lighting is now being provided using fiber optic lighting systems or low-voltage lighting systems. Kool Decks are sometimes made of pavers or stone without reinforcing steel. The steel used within the pool walls is not always being tied into the Kool Deck reinforcing in order to address expansive soil conditions. Pools shells and Kool Decks are also being built out of fiberglass reinforced concrete that has no steel reinforcement, or the steel reinforcing is epoxy coated to address corrosive environments. We have been discussing conductive pool shells and decks so far, but pools are also being built completely out of fiberglass, or pool shells have vinyl liners over the structure itself.

What are the requirements of Article 680 that address these new types of installation?

Figure 1. The above is a slide from the upcoming Analysis of Changes NEC-2008. The Code is consistently evolving to encompass the latest methods and materials to provide the safest environment possible for users of such things as swimming pools. This sect

There have been many reports of stray currents being felt by swimmers in pools. These stray currents can come from many sources; some are from faulty wiring or equipment around pools, and others are currents caused because of a failure of current-carrying conductors in the utility service laterals. No matter what the cause of these stray currents, they need to be safely handled to keep swimmers from becoming grounding conductors themselves.

InNEC-2005, the bonding requirements of Article 680 were expanded, and equipotential bonding was introduced in Section 680.26. In 680.26(A), there is an explanation as to what the intent of this bonding system is. Its purpose is "to eliminate voltage gradients in the pool area”; it is not designed to eliminate current flow, but to control it.

NEC 680.26 addresses this by creating an equipotential bonding system within and around the pool area. This system as required in 680.26(B) includes the bonding of metallic structural components of the pool and deck. This requires all of the metal structural steel within the pool shell, coping stones, and deck to be bonded together using approved connections. This section also requires that if reinforcing steel "is encapsulated with a nonconductive compound,” such as epoxy-coated rebar, "an alternate means to eliminate voltage gradients” is to be provided. This alternate means is specified in Section 680.26(C)(3). Article 680.26 also requires that forming shells used for underwater lighting, certain metal fittings, all metal within 5′ of the pool, and electrical equipment associated with the pool be bonded together using a #8 copper conductor and approved connectors. All lugs or connectors need to be listed for their application. When a connector is buried within concrete or underground, it needs to be listed for concrete encasement or for direct burial.

In Article 680.26(C), the equipotential bonding grid is outlined. In order to understand this section better, remember to refer to TIA 05-2, which was approved to add clarity. This section requires that an equipotential bonding grid be established under or within the bottom and sides of the pool shell and also extend 36″” from the walls of the pool within or under paved walking surfaces of the pool deck. The TIA eliminates the requirement for the equipotential bonding grid being installed behind the walls and bottom of a pool made completely of fiberglass or a pool that is completely lined with a vinyl polymer.

Section 680.26(C)(1) requires that the bare structural reinforcing steel of the pool structure be bonded as required by 680.26(B)(1) and requires this steel to be bonded to the deck reinforcing steel using a #8 copper conductor. Section 680.26(C)(2) requires the walls of a metal pool to be part of the equipotential bonding grid. Section 680.26(C)(3) addresses the alternate means of bonding required when structural steel is not used in the pool structure or deck or when the structural steel is encapsulated with a nonconductive compound. This alternate system requires a grid of bare #8 AWG wire to be installed within or under the pool shell and to extend 36″ beyond the pool walls under the deck. This grid is laid out in a 12″ by 12″ pattern, similar to the pattern usually required for reinforcing steel.


If we do not adopt and enforce the latest electrical codes that address these new materials and practices, incidents of electrical accidents may increase in the future. Pools are now being constructed differently and require the NEC to keep up with these new methods and materials and to require electrical installations that are safe. If you are under an NEC edition older than 2005 and an alternate material or method is proposed for pool construction that would pose a problem addressed by NEC-2005 requirements, you may wish to stipulate the requirements of NEC-2005, Article 680, in the letter of modification approved for using these alternate methods and materials, as allowed in the building code.

We all need to keep up with the changing times and the new methods of construction that are being developed. In order to keep up, the NEC is updated at least every three years, and even with this three-year-cycle it seems like we are always behind the new technology being developed. Having participated in the 2008 NEC Report on Proposals (ROP) and Report on Comments (ROC) processes, I can just say that changes are still on the way for this section, not only to clarify the code language but also to address new problems presented during this new cycle.

Read more by Jim Maldonado

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Isolated Power Systems in Health Care Facilities

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

Grounded Systems Generally Required

Photo 1. Health Care Facility Room

Generally, electrical systems used in power distribution systems for premises wiring are required to be grounded. The NEC includes rules that often make this determination. Some electrical systems are required to be grounded, while other systems are permitted to operate ungrounded (see 250.20 and 250.21). Then there are those systems that are not permitted to be grounded (see 250.22). One such ungrounded electrical system is the isolated power system utilized in health care facilities. This article focuses on some key installation requirements for these systems, and also takes a look at essential elements of installing and inspecting these ungrounded electrical systems.

Brief Look at the History

In early years of health care methods and procedures, the anesthetics utilized were mostly of the flammable types. Even prior to the use of electricity for medical equipment and appliances, the challenges of flammable anesthetics presented themselves often with resultant injuries and many deaths. Explosions and fires were linked to ignition of flammable anesthetics (such as ethylene ether) by open flames of candles as well as static electricity and other sources. The problem had escalated to frequent occurrences of these types of accidents in the health care world. The committee on health care facilities was formed in the 1930s to deal with this as well as many other challenges. This committee work was the initial development of what is now known in the codes and standards world as NFPA 99, the health care code.

Photo 2. Nonflammable anesthetics in a gas storage room of a hospital

TheNECdealt with electrical installation provisions for health care facilities generally in the early editions of the document. The practice of medicine and medical procedures in health care was also paralleled with the practice and learning stages of the safe use of electrical power in these early times. The ignition component of the fire triangle, and the fire triangle itself were discovered and had to be dealt with in health care facilities as well as in other occupancies. In the early editions of the NEC (1930s through the 1950s), the Code included provisions for health care facilities only generally, but did include a section (5135) on combustible anesthetics under Article 510 on hazardous locations in the early 1950s. In the code cycles to follow, the NEC continued to include information and provisions for combustible anesthetics under Article 510 through the early 1960s. In NEC-1965, Article 517 was formed and titled "Flammable Anesthetics.” That title was changed from "Flammable Anesthetics” to "Health Care Facilities” in development of NEC-1971. Many of the provisions contained in Article 517 at that time were electrical provisions already contained in NFPA 99. Health care facilities electrical rules and provisions were now included as a special occupancy in the NEC, and rules for flammable anesthetics as well as other electrical requirements for health care facilities had arrived.

Use of Isolated Power Systems

Photo 3. Isolated power systems are required to be listed

Isolated power systems were a method of dealing with flammable anesthetics in early Code rules. By operating the electrical system ungrounded, the arc from a first ground fault is minimized. This type of system helped minimize the hazards of ignition of flammable gases during health care procedures and operations. Other methods of reducing ignition sources, such as static electricity, are conductive operating room floors and equipotential grounding and bonding to reduce the likelihood of current flow across to conductive surfaces that might be at different electrical potentials. Some operating rooms still have evidence of first generation protective techniques utilized in preventing fires and explosions. This evidence might be in the form of the old conductive flooring with the occasional drag chain hanging from old rolling metal operating room tables. Isolated power systems were utilized heavily as one of the primary protection techniques in operating rooms and critical care locations of health care facilities. These systems are still in use, although many of the problems with flammable anesthetics are significantly fewer in numbers. Nonflammable anesthetics have replaced the common use of the flammable types (see photo 2). There are areas and other countries that still utilize the oxygen inspired gases that are flammable and some laboratories in health care facilities might require use of flammable gases. The hazardous (classified) locations associated with flammable anesthetizing locations are still delineated in Article 517. Part IV of Article 517 continues to include the requirements for electrical wiring and equipment in an anesthetizing location of a heath care facility that is classified as a hazardous (classified) location.

Ungrounded System Characteristics

Photo 4. The transformers of isolated power systems are typically of low kVA capacity.

When an electrical system is operated ungrounded, there is no solid reference to ground from any of the conductors supplied by the secondary of such systems. A few key advantages of such systems include minimal arcing effects from a first phase-to-ground fault condition. Another benefit is continuity of service (uninterrupted power) of such systems. A third benefit is reduced shock and electrocution hazards from phase-to-ground contact with such systems. These systems provide an equal and effective form of electrical safety for health care facilities. As with other ungrounded systems, these systems must be monitored and operated by qualified persons. Isolated power systems operate ungrounded, but a line isolation monitor is required to continuously monitor leakage current from each phase conductor supplied by the system as part of this listed equipment. This monitor detects leakage current to ground in the milliamp threshold range of not greater than 5 mA similar to high-impedance grounded neutral systems and ungrounded systems with ground detectors. When the line isolation monitor of an isolated power system provides annunciation of leakage current beyond the acceptable limits, appropriate corrective action is required by qualified personnel. This usually includes discontinued use by medical personnel at first, then corrective actions by facilities maintenance staff thereafter. Common causes for alarm conditions identified by line isolation monitors of isolated power systems include, but are not limited to, equipment or medical appliance insulation failures as well as breakdown on insulating in electrical circuitry supplied by such systems. While breakdown of the insulation of the isolated power-system branch circuits is possible, the monitor usually detects leakage currents when dielectric insulation in equipment or appliances fails. An important protection feature of these isolated ungrounded systems is the continuity of electrical service that they provide even with an insulation failure. This allows the power to remain on for these systems that are supplying life support equipment and other critical care apparatus essential to the well-being of patients receiving treatment in locations supplied by isolated power systems.

Listing Required

Photo 5. Infant is being kept alive by life support equipment supplied from an isolated power system.

Isolated power systems are required to be listed as indicated in 517.61(A)(2) [see photo 3]. This means the system is listed to an appropriate electrical safety standard (see UL Standard 1049). This also means that specific instructions and guidelines for use will be required for proper installation and inspection of such systems.

A couple of key areas of concern are the dielectric values associated with the branch-circuit conductors supplied by the isolated power system. Since the system is measuring leakage current to ground in the milliamp range, conductor and system insulation are important. This is a primary reason that these listed systems are kept at low kVA transformer ratings, usually below 10 kVA (see photo 4). This helps minimize the amount of leakage capacitance on the secondary side of the isolation transformers used in these systems.

Isolated Power Systems Required

Photo 6. Life support equipment used in a critical care patient location of an intensive care unit

The decision on when to use isolated power systems in health care facilities depends on the patient care area and the characteristics of the electrical system supplying the patient care area. For example, isolated power systems are permitted as an optional protection technique for critical care locations of health care facilities [see 517.19(E)]. This rule became optional in NEC-1996. However, isolated power systems become a requirement and not an option when wet procedure locations, as defined in 517.2, preclude the use of ground-fault circuit interrupters (GFCIs) where interruption by GFCI devices cannot be tolerated (see photos 5 and 6). In this case, the protection technique must be provided by an isolated power system [see 517.20(A) and (B)]. Once the isolated power system becomes a requirement, it must be listed equipment and installed to meet all applicable rules in 517.160.

Wet Procedure Locations

Photo 7. XHHW conductor insulation used on branch-circuit conductors supplied by an isolated power system.

The definition title wet locations in 517.2, under "Patient Care Area,” has been revised for the NEC-2008 to wet procedure location. This revision provides more specific criteria of the wet locations covered by the definition in 517.2 and provides a bit more differentiation from the wet location definition in Article 100. See IAEI’s book, Analysis of Changes NEC-2008 for additional information about this revision.

Isolated Power System Branch-Circuit Conductors

Isolated power systems and their proper installation and use involve specific criteria. Insulation and identification of the branch-circuit conductors is more specific than that allowed in the general rules of the Code. The dielectric insulation resistance values are critical for system functionality. Minimizing the length of branch-circuit conductors and using conductor insulations with a dielectric constant less than 3.5 and insulation resistance constant greater than 6100 megohm-meters (20,000 megohm-ft) at 16°C (60°F) reduces leakage from line to

Photo 8. Brown and orange XHHW conductors installed for isolated power-system branch circuits

ground, reducing the hazard current. THHN/THWN typically do not offer these high dielectric insulation resistance values. XHHW is one type of conductor insulation that meets the dielectric insulation values required by these systems (see photo 7). The manufacturer’s instructions and installation guidelines for these systems will often specify the type of conductor insulation required or acceptable for use with the particular system. Sometimes a maximum length for the circuits is also specified. Wire-pulling compounds that have a deterioration effect on the dielectric values of conductor insulation are not permitted to be used when installing these branch-circuit conductors [see 517.160(A)(6)].

Branch-Circuit Color Code Required

The Code does not include a color code for general wiring branch-circuit conductors. However, there is a specific color code required for the branch-circuit conductors supplied by the isolated power system. Section 517.160(A)(5) requires the branch-circuit phase conductors to be orange (for conductor No. 1) and brown (for conductor No. 2) (see photos 8 and 9). Yellow is the required color for the third conductor if a three-phase isolated power system is used.

Photo 9. Brown and orange XHHW conductors installed for isolated power-system branch circuits

NEC-2008 Update: As of this writing, Section 517.160(A)(5) has been revised to require that the orange, brown, and yellow conductors used with isolated power systems are now required to be identified with a distinctive colored stripe other than white, green, or gray. See IAEI’s book, Analysis of Changes NEC-2008 for additional information about this revision.

Where the isolated power system branch circuits supply 125-volt 15- or 20-ampere receptacles, the orange conductor is required to be connected to the terminal on the receptacle intended for the grounded conductor (see photo 10). Since there is no grounded conductor supplied by these systems, this clarification was made inNEC-1999.

Grounding and the Reference Grounding Terminal

Photo 10. Orange ungrounded circuit conductor is required to be connected to the receptacle terminal that is normally intended for a grounded conductor.

Although the isolated power system itself is ungrounded, equipment grounding conductors are required to be installed to the receptacles and connected to the grounding terminal of such receptacles to serve as a ground reference for connected equipment or appliances. The equipment grounding conductors associated with the isolated power system branch circuits are permitted to be installed either inside the conduit or raceway or on the outside of the raceway. This is in contrast to the requirements of 300.3(B) and 250.134, which generally require the equipment grounding conductor to be run in the same raceway, cable, or trench. This minimizes the effects of impedance in the equipment grounding circuit in ground-fault conditions for normally grounded systems. The need is different for ungrounded (isolated) systems because the systems are monitoring leakage current and will not facilitate an overcurrent device in the event of a single phase-to-ground fault from any of the ungrounded conductors of the system. It is recommended to install the equipment grounding conductor in the raceway with the circuit conductors. This offers greater protection in the event of a second phase-to-ground fault condition on the system [see 517.19(F)]. The equipment grounding conductors with the branch circuits of isolated power systems are required to be connected to the reference grounding bus in the listed isolated power system equipment. This reference grounding bus is connected to the equipment grounding conductor supplied with the primary circuit feeding the isolated power system (see photo 8). If there are any electrostatic shields present with the system, they are required to be connected to the reference grounding bus within the equipment. This is also required by NFPA 99.

Photo 11. Line isolation monitor of an isolated power system (digital)

Where isolated power systems are used to supply power circuits to task illumination, selected receptacles, and fixed equipment in critical care areas that utilize anesthetizing gases, or the system is used in special environments, the isolated power system is required to be supplied by a circuit that supplies no other load. This circuit is required to be connected to the critical branch of the emergency system, which is part of the essential electrical system [see 517.30(C)(2)]. Circuits supplying primary side of isolated power system transformers must not operate at more than 600 volts between phase conductors and are required to be protected with properly rated overcurrent devices. The equipment grounding conductor with the primary circuit for the isolated power system is required to be not less than the sizes given in Table 250.122, based on the rating of the primary overcurrent device supplying the isolated power system.

Line Isolation Monitor

Photo 12. Line isolation monitor of an isolated power system (analog)

The use of an isolated power system requires, as part of the system, a line isolation monitor (LIM) that is installed so as to be visible to personnel in the care areas where the isolated power circuits are used. The line isolation monitor includes a green (status OK) lamp and a red (hazard leakage current) lamp, both of which are to be visible by personnel (see photos 11 and 12). The monitor is supplied as part of the isolated power system panel, but many times remote monitors are installed where the equipment is located outside the critical care area. An audible warning signal is initiated when the total hazard current (consisting of possible resistive and capacitive leakage currents) from either isolated conductor to ground reaches a threshold value of 5 mA under nominal line voltage conditions. The line monitor is not required to alarm for a fault hazard of less than 3.7 mA or for a total hazard current of less than 5 mA [see 517.160(B)(1)]. It is often a desirable design specification to locate the ammeter and LIM so that they are conspicuously visible to persons in the anesthetizing location.

System Testing

Isolated power systems are tested for acceptance upon initial installation for insulation resistance values and potential differences to the reference grounding bus in the equipment. Although the NEC does not require initial performance testing of these systems, this testing is a requirement of NFPA 99 and must be performed periodically thereafter. If the system is modified or altered after initial installation, it must be tested again. The manufacturers of isolated power systems often provide this service when the systems are first installed. Many testing organizations can also provide these testing services. Many of the major health care facilities perform these tests on a regular schedule with their own trained qualified personnel. Appropriate records are required to be kept of such tests. See NFPA 99 for specifics on these types of tests and required testing time frames.


Isolated power systems were primarily utilized as a protection technique to minimize the possibilities of explosions and fires in flammable anesthetizing locations in health care facilities. Areas in health care facilities that utilize flammable anesthetics are classified as hazardous locations and require isolated power systems as well as other hazardous (classified) location wiring and protective techniques. Isolated power systems are still utilized, but more as an optional protection technique or as required in wet procedure locations as defined in Article 517 because interruption of power by ground-fault circuit interrupters cannot be tolerated. The isolated power system provides an equal and effective means of electrical safety for the patient and personnel in health care facilities. These special systems are operated ungrounded, but must be monitored. Not only is it important to install these systems correctly and test them upon initial installation for acceptability, but it is equally important that the personnel utilizing such systems be trained and qualified in their proper use. This includes both the electrical staff and the medical personnel providing the patient care in these critical care areas. The authority having jurisdiction should work closely with installers when such systems are being installed in the health care facilities. Installation instructions and recommended testing criteria provided in the installation instructions and the applicable codes and standards are of critical importance for installers as well as inspectors. Chapter 5, Special Occupancies, many times modifies the rules in chapters 1 through 4 to be more restrictive. The installation of isolated power systems is one such case and is worth a closer look. This article is not totally inclusive of all situations and uses of isolated power systems, but does cover many of the requirements.

Read more by Michael Johnston

Tags:  Featured  July-August 2007 

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To Build Wealth, Look at Both Sides of the Balance Sheet

Posted By Jesse Abercrombie, Sunday, July 01, 2007
Updated: Sunday, February 10, 2013

At a recent golf tournament for the construction industry, I spoke with a gentleman about a once very successful contractor who is no longer in business. I instantly figured that the gentleman had sold his business and pursued other endeavors. However, I found out that although he was successful, every dollar he made was spent on homes, cars and boats. This isn’t as common in the construction industry as it is in other industries, but I see more and more business owners get leveraged right out of business.

To achieve your financial goals, you need to be a diligent saver and investor. But you need to do more than just build your assets; you also must do a good job of managing your debts. If you let your debts get out of control, they will eventually erode your savings and investments—and when that happens, the road to financial success can get pretty bumpy.

Unfortunately, your fellow Americans are doing a poor job of saving money and staying out of debt. Here are some telling statistics:

  • Debt is rising.By September 2006, household debt had reached 130.9 percent of disposable income, according to the Center for American Progress. In plain English, that means we owe about a third more than we have available to spend after we’ve paid our taxes and met our expenses.
  • Savings have fallen.For most of 2005 and all of 2006, the personal savings rate was negative, according to the U.S. Commerce Department. Previously, we haven’t had a negative savings rate since the Great Depression. In short, we’ve gotten into the habit of spending more than we save.

These grim figures foretell a discouraging financial future for many of us. Every dollar you pay for debt is a dollar you can’t use to invest. Furthermore, if you have too little in savings, you may well be forced to dip into your existing investments to pay for short-term needs, such as a business expense like a new truck or repair to your existing fleet. And the more you take from your investments today, the less you will have available tomorrow when you might need the money to help pay for retirement or your children’s college tuition.

So what can you do to protect your savings and investments against the demands of debt? You probably already are familiar with some steps you can take to cut costs: Extend the life of your fleet, eat out less often, look for cheaper phone and cable service, etc. Especially, watch your phone bill at your company. In short, review your entire lifestyle, and try to separate the "nice to have” items from the "must have” ones. If you can reduce your expenses, you can start whittling away at your debt.

While you’re taking steps to cut your costs, you can still add to your investments. How? For starters, increase your contributions to your 401(k) or other employer-sponsored retirement plan every time your business achieves growth. Until you retire, you generally won’t be able to access this money without taking a big tax hit, so you won’t be tempted to "raid” your 401(k) to pay off debts. [You can, however, typically take loans from a 401(k) or similar account.]

You also may want to "pay yourself first.” Each month, before you pay the mortgage, the utility companies and your other obligations, set aside an amount for your investments. It’s easier if you set up a bank authorization to move the money directly into the investment you choose. By having the money taken out this way, you are less likely to "miss” it—and, hopefully, you’ll be less likely to look at it as a source of funding for your daily life.

By cutting your debts, boosting your 401(k) contributions and paying yourself first, you can help yourself get a firmer grip on your financial situation—today and tomorrow.

Read more by Jesse Abercrombie

Tags:  Featured  July-August 2007 

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What are you paying for electricity? Part 3, Commercial Electric Rates

Posted By David Young, Sunday, July 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. In this segment, I am going to share with you and discuss in detail the small commercial 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. Some of the terms I am using in this article have been previously defined and discussed in parts 1 and 2 of this series.

Photo 1. Typical small commercial businesses.

Medium General Service Rate

For our example utility, their medium general service rate is available to any customer having a monthly energy use exceeding 3,500 kWh and a summer maximum measured fifteen-minute demand of less than 300 kW. This is the basic rate for most small commercial customers. For our example utility, this rate has a customer charge of $25.42 per month. The energy charge is 6.2533 cents per kWh in the summer months and 6.9533 cents per kWh in the winter months. The demand charge is $22.6935 per kW in the summer months and $14.7419 per kW in the winter months. The measured demand is the greatest demand established by the customer during any fifteen-minute period of the month taken to the nearest whole kilowatt, but not less than 1 kW. Note that the demand is not time dependent. On this rate, hitting a peak fifteen-minute demand at 2 a.m. is just as expensive as one at 2 p.m.

Table 1. Medium General Service Rate

For a restaurant that uses 24,000 kWh of energy with a 150 kW demand in a summer month, the bill will be $1,500.79 for energy, $3,404.02 for demand, and $25.42 for customer charge. The demand charge is over two times the energy charge. If load management can be done to reduce the demand, a significant savings can be achieved. In one such case with which I was involved, a few hundred dollars of electrical work saved a restaurant thousands of dollars in their electric bills each month. The dining area of the restaurant was air-conditioned with two units. Under the worst case outside temperature conditions, the two units were each on less than half the time. This meant the units could be operated one at a time, and they would still maintain the desired temperature. The owner had an electrician wire the controls so that only one unit could be on at a time. The unit that operated more frequently (the one that cooled the area closest to the kitchen) was designated the primary unit. If the primary unit was on, the other unit could not turn on until the primary unit’s thermostat was satisfied. The result was a fifty percent reduction in the air conditioning demand. The air conditioning demand was a large piece of the restaurant’s total demand. For a restaurant that uses 24,000 kWh of energy with a 150 kW demand each month in the summer months and 16,000 kWh of energy with a 100 kW demand each month in the winter months, the annual bill would be $40,617.96 on this rate.

Medium General Service Off-Peak Rate

Table 2. Medium General Service Off-Peak Rate

Our example utility has an optional service very similar to the above rate except that the demand is only measured during on-peak hours. For this rate, on-peak hours are 6:00 a.m. to 10:00 p.m. Monday through Friday. During Daylight Savings Time, on-peak hours are 9:00 a.m. to 10:00 p.m. Monday through Friday. Note that the on-peak hours during Daylight Savings Time (summer) are very different from the normal on-peak hours. Since the on-peak time starts at 9 a.m. in the summer, turning on the air-conditioning system well before 9 a.m. to cool the building down is usually a good cost saving move. All the charges are the same as the medium general service rate except there is an additional service charge of $8.99 per month. Because the customer pays the additional service charge, the utility ignores off-peak demand. Under this rate, if you use equipment like elevators that use a lot of power for short periods of time during off-peak hours, you pay for only the energy associated with the use of the equipment. Under this rate, a small commercial establishment that uses 24,000 kWh of energy with a 130 kW on-peak demand each month in the summer months and 16,000 kWh of energy with a 90 kW on-peak demand each month in the winter months, would have an annual bill of $37,731.00.

Medium General Service Space-Heating Rate

Table 3. Medium General Service Space-Heating Rate

Our example utility also has an optional service for customers where at least one third of the demand during the heating season is from electric resistance heat or electric heat pump. For this rate, during the months October through May, the billing demand will be reduced by 75% of its excess, if any, over the greatest billing demand of the previous billing months of June through September. For example, if the measured demand for the month of December was 200 kW and the previous summer maximum demand was 100 kW, the customer’s billing demand for December would be 125 kW.

Billing demand = 200 kW – 0.75
x (200 kW – 100 kW) = 125 kW

The charges for this rate are the same as for the medium general service rate. Under this rate, a small commercial establishment with electric heat that uses 24,000 kWh of energy with a 100 kW demand each month in the summer months and 30,000 kWh of energy with a 200 kW demand each month in the winter months, would have an annual bill of $46,815.44. If the same customer were on the Medium General Service Rate, they would pay $8,845.16 more each year.

Next time, in Part 4, I will get into the details of the rates that apply to large commercial and industrial facilities.

Read more by David Young

Tags:  July-August 2007  Other Code 

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