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Connecting IT Equipment

Posted By Keith Lofland, Thursday, March 01, 2012
Updated: Monday, February 04, 2013

Question

Can information technology equipment be cord-and-plug connected if the cord is either hard usage type or portable power cable type? Is such IT equipment required to be marked as being suitable for cord-and-plug connection before such connection be utilized? Is there a maximum length for power-supply cords used to connect IT equipment as well as for cables that interconnect separate IT equipment? JP

Answer

First, we must assume that the information technology equipment in question does qualify as IT equipment by meeting all of the six conditions listed at 645.4. If the IT equipment in question does not meet all of the special conditions of 645.4, then this equipment would be subject to the provisions of Chapters 1 through 4 of theNEC.
 
Figure 1. Typical IT equipment, cord-and-plug connected under a raised floor.

Section 645.5(B)(2) covers the type of cords that are permitted for IT equipment and the terms "hard usage” and "portable power cable” are not used in this section. This subsection does require IT power cords to be listed and of a type permitted for use on listed information technology equipment. Section 645.5(B)(2) also permits power cords constructed of listed flexible cord and listed attachment plugs and cord connectors of a type permitted for information technology equipment. Section 645.4(3) requires all information technology equipment to be listed and the determination of whether the IT equipment can be cord-and plug-connected is better suited for the product standards and the product certifications rather than theNEC. From the UL White Book Category "NWGQ” the following is stated, "When listed equipment intended for use with a detachable power-supply cord is not provided with such a cord, a cord suitable for connection of the equipment to the branch circuit should be separately provided.” The length of the power-supply cord for IT equipment is limited to 4.5 m (15 ft) by Section 645.5(B)(1). Interconnecting cables are not limited to 4.5 m (15 ft) like the power-supply cables as noted at 645.5(C). Interconnecting cables are required to be listed but the length of the interconnecting cable is not restricted by theNEC.

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Tags:  Focus on the Code  March-April 2012 

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Question: When installing a supply-side bonding jumper, what are the requirements for installing such a conductor both inside and outside a raceway? What type of conductive material is suitable for a

Posted By David Williams, Sunday, January 01, 2012
Updated: Monday, February 04, 2013

Question

When installing a supply-side bonding jumper, what are the requirements for installing such a conductor both inside and outside a raceway?What type of conductive material is suitable for a supply-side bonding jumper and how is it sized? EJ

Answer

The term supply-side bonding jumper first appeared in the 2011 National Electrical Code as a result of a CMP-5 Task Group regarding the proposed revisions to Section 250.30 for grounding separately derived systems.

This revision created a new definition that was added to Section 250.2. "Bonding Jumper, Supply-Side. A conductor installed on the supply side of a service or within a service equipment enclosure(s), or for a separately derived system, that ensures the required electrical conductivity between metal parts required to be electrically connected.”

Previously, we identified all bonding jumpers the same, whether they were on the supply side of an overcurrent device or if they were on the load side of an overcurrent device. By designating it as a supply-side bonding jumper, it is easier to understand how the conductor is used and how to size it properly. A bonding jumper on the supply side of an overcurrent device is sized from Section 250.102(C), which takes you to Table 250.66. The size of the supply-side bonding jumper is based on the ungrounded phase conductors. An equipment bonding jumper on the load side of an overcurrent device is sized from 250.102(D) based on Table 250.122, similar to sizing an equipment grounding conductor from the rating of the overcurrent devices protecting the conductors of the branch circuit or feeder.

A supply-side bonding jumper installed on the inside of a raceway must be installed with the circuit conductors from the source enclosure to the first disconnecting means. Section 250.104(E) governs how the bonding jumper is to be installed: (1)inside the raceway, it must comply with 250.119: bare, covered, or insulated. If covered or insulated, it must be green or green with yellow stripe(s); (2)outside the raceway or enclosure, it generally cannot exceed 6 ft in length and must be routed with the raceway or enclosure. There is an exception for outside pole locations allowing the jumper to be longer than 6 ft for isolated sections of metal conduit or raceway.

The supply-side bonding jumper is sized per Table 250.66 based on the size of the ungrounded phase conductors. It is not required to be larger than the ungrounded phase conductors. Section 250.102(A) states that bonding jumpers may be of copper or other corrosion-resistant material, and may be a wire, bus, screw, or similar suitable conductor.

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Tags:  Focus on the Code  January-February 2012 

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Question: Where branch-circuit conductors pass through a panelboard and do not originate or terminate in that panelboard, is there any requirement for identifying where the overcurrent devices are loc

Posted By Keith Lofland, Sunday, January 01, 2012
Updated: Monday, February 04, 2013

Question

Where branch-circuit conductors pass through a panelboard and do not originate or terminate in that panelboard, is there any requirement for identifying where the overcurrent devices are located for these pass-through conductors? TG

Answer

In this instance, the panelboard is serving the function of a pull box for these pass-through conductors. A panelboard is permitted for this purpose if proper wire bending space is provided as per 408.55. Feed-through conductors are permitted in a cabinet that contains overcurrent devices (such as a panelboard) per 312.8. One of the conditions required by 312.8 in permitting this application is that a warning label is required to be applied to the enclosure that identifies the closest disconnecting means for any feed-through conductors. This is a new requirement for the 2011 NEC.
— Keith Lofland, CMP-9


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Tags:  Focus on the Code  January-February 2012 

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Question: Both dc and ac photovoltaic systems in a common enclosure?

Posted By James Rogers, Tuesday, November 01, 2011
Updated: Monday, February 04, 2013

Question

Where conductors from both dc and ac photovoltaic systems utilize a common junction box or other enclosure, are there any special identification requirements for these conductors? Also, where photovoltaic circuits are run inside a building (whether in conduit or not), can these circuits be run embedded within insulation, and if so, is there any derating of such conductors required? E.C.

Answer

Section 690.4 is the first section of the 2011NECthat covers the installation raised in the first portion of your question. There seems to be one summation that is being made for clarity, the question inquires about "both dc and ac photovoltaic systems.” The summation being made deals with a common junction box where the PV output circuit conductors and the inverter output circuits are both present on an interactive system.

This being clarified, 690.4(B) states, "Photovoltaic source circuits and PV output circuits shall not be contained in the same raceway, cable tray, cable, outlet box, junction box, or similar fitting as conductors, feeders, or branch circuits of other non-PV systems, unless the conductors of the different systems are separated by a partition. Photovoltaic system conductors shall be identified and grouped as required by 690.4(B)(1) through (4). The means of identification shall be permitted by separate color coding, marking tape, tagging, or other approved means.”

Looking at the original proposals that were submitted for this clarifying change in the 2011NEC, Proposal 4-183 and Proposal 4-184, the submitter intended that whenever they were part of the same "PV system” that both the ac and dc conductors could be contained in the same box or enclosure provided they are properly grouped and indentified.

One of the problems that arises here is that the current language can still lead to confusion on the part of the installer and the enforcer. In 690.2 the definition ofPV output circuitis as follows, "Circuit conductors between the photovoltaic source circuit(s) and the inverter or dc utilization equipment.” The definition ofinverter output circuitis as follows, "Conductors between the inverter and an ac panelboard for stand-alone systems or the conductors between the inverter and the service equipment or another electric power production source, such as a utility, for electrical production and distribution network.”

When you look at these definitions, the allowance does not clearly extend to the inverter output circuits, commonly the multiwire branch circuit from the inverter to the ac panelboard, as being allowed in the same enclosure even though that was the intent of the submitter in the substantiation. To that extent, I understand the confusion that you may have on this requirement and acknowledge that CMP-4 needs to further clarify this in the 2014NEC.

At this point in time, it is my opinion that the conductors from the same system, both ac and dc, can occupy the same box or enclosure provided, as stated above, that they are properly grouped and identified. The other thing to remember here is that all of the Chapter 3 requirements for whatever wiring method is utilized also need to be complied with, including conductor insulation rating, conditions of use and terminal temperature ratings.

A very similar issue exists with the installation of multiple PV systems on the same roof top. These could be ac, dc or both. The conductors from these multiple systems must also be run from the roof top into the building or structure. In my opinion, CMP-4 also needs to address this issue. Any proposals or documented field experience that is submitted to CMP-4 through the NFPA proposal system would be beneficial to everyone.

That brings us to the second portion of the question as to whether or not PV circuits (in or out of conduit) run inside of a building or structure need to consider adjustment and correction factors, especially where run through thermal building insulation. Section 90.3 of theNECstates that Chapters 1 through 4 apply generally unless supplemented or modified by Chapters 5, 6 or 7. Part IV of Chapter 690 addresses the acceptable wiring methods for use when installing a PV system on a building or structure and it does not contain any modification to the installation requirements for wiring methods installed in or through thermal building insulation. So the answer to the question is yes, PV conductors installed in an acceptable wiring method can be run in or through thermal building insulation; and yes, any correction or adjustment factors that are required for the applicable wiring method must be considered.

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Tags:  Focus on the Code  November-December 2011 

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Question: Single receptacle for a refrigerator?

Posted By Bill McGovern , Tuesday, November 01, 2011
Updated: Monday, February 04, 2013

Question

Do I need to install a single receptacle for a dwelling unit refrigerator if I install a 15-ampere individual branch circuit by employing Exception No. 2 to 210.52(B)(1), or can I install a duplex receptacle for this appliance? I see a duplex receptacle installed in this application all the time, but the individual branch circuit thing makes me think this might need to be a single receptacle. JL

Answer

A single or duplex receptacle is acceptable in this situation. Section 210.52 addresses the requirements for dwelling unit receptacle outlets. Part (B) of this section covers the requirements for receptacles installed in the kitchen and other associated areas that will serve portable appliances along with refrigeration equipment. Exception No. 2 to 210.52 (B)(1) allows a receptacle for refrigeration equipment to be supplied from an individual branch circuit rated 15 or 20 amperes instead of the 20-ampere-rated small appliance branch circuit as specified in 210.11(C)(1).

It is best to understand what an individual branch circuit exactly is. Article 100 defines an individual branch circuit as: "A branch circuit that supplies only one utilization equipment.” Installing a duplex receptacle and connecting only a single piece of refrigeration equipment is not in violation of the Code in my opinion nor is it the opinion of Code-Making Panel 2.

A proposal (2-239) similar to this question was submitted at the Report on Proposal (ROP) stage for the NEC 2011 code cycle and was rejected with the following panel statement: "The panel does not agree that a single receptacle is required. A receptacle other than a single receptacle could be used and other means such as configuration or arrangement of the equipment could limit the application to a single utilization equipment.” A duplex receptacle occupying a dedicated space behind the refrigerator would not allow for the use of the other contact device, or the connecting tabs between the conductor terminals could be removed making the other contact device inoperable.

A similar situation may be the installation of a 110-ampere service using 2 AWG copper service conductors and Class J fuses. A 200-ampere fusible service disconnect would be required to accommodate the 110-ampere fuses. It would only be a violation to install overcurrent protection in excess of 110 amperes but the equipment involved would easily allow fuses greater than 110 amperes. It is always important to remember to check with the local authority having jurisdiction (AHJ) when in doubt of a specific interpretation.
—Bill McGovern, CMP-2

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Tags:  Focus on the Code  November-December 2011 

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Question: Protect grounding electrode conductor in crawl?

Posted By Michael Johnston, Thursday, January 01, 2009
Updated: Monday, February 04, 2013

Question

Section 250.64(B) states where exposed and on a surface, a grounding electrode conductor should be protected. If I sleeve an 8 AWG GEC in rigid nonmetallic conduct from the service panel to the crawl, do I have to protect the GEC in the crawl, or is it ok to run the GEC on the bottom of the floor joists without protection to the water pipe? It’s a 100-amp service with 2 AWG copper. Does that last sentence apply to the whole length by 250.64?

Personally, I don’t think it is subject to being physically damaged in the crawl. The crawl is a little less than 3′ high. — A. C.

Answer

You are correct in your understanding of this rule. The last sentence of 250.64(B) requires an 8 AWG copper grounding electrode conductor to be protected from physical damage by installing it in rigid metal conduit, rigid nonmetallic conduit, intermediate metal conduit, electrical metallic tubing, or cable armor, and no exceptions to this requirement. If the conductor is a 6 AWG, it could be judged as not subject to physical damage in the installation you’ve described in the question. As I see it, the solutions are to either size up to 6 AWG or protect it with one of the methods specified in 250.64(B). As always, consult the local approving inspector/AHJ for any local requirements or interpretations. I hope this helps with your question. — Michael J. Johnston, CMP-5

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Tags:  Focus on the Code  January-February 2009 

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Breakers not listed on panelboard data sheet

Posted By Lanny McMahill, Thursday, January 01, 2009
Updated: Monday, February 04, 2013

Question

I would like some advice and general guidance regarding the use of breakers that are not listed on the panelboard data sheet. Some of these panels have not been made in twenty years and the company is out of business. I generally recommend finding surplus breakers on the internet. Most electricians try to get by with breakers that physically fit and if those are rejected, they might get a "classified” breaker. My understanding is that the "classified” breakers are listed for use in specific panels (which is not disclosed in the marketing literature). Am I correct in believing that unless the breaker is listed for use in the specific panel that it is to be used in, it does not meet the code requirement of listed and labeled? — J. C.

Answer

First, it is understandable that for older panelboards it is difficult to find new or replacement circuit breakers. Typically, the panelboard may be obsolete, the manufacturer may be out of business or perhaps purchased by another manufacturer. In addition, electrical equipment design and manufacturing technologies change. As a result, the equipment is not produced or there is little demand for such equipment.

Second, it is imperative to note that it is not good to encourage the use of "surplus breakers” or "breakers that physically fit.” Doing so could create a potentially unsafe condition. Obviously, it is difficult to determine the operating condition of a surplus circuit breaker, and simply because a circuit breaker fits in a panelboard does not make it correct for installation and use. Since safety is paramount in any electrical installation, the installation and use of appropriate equipment is necessary!

Third, as you have noted, classified circuit breakers are intended for installation and use in specific panelboards. Such circuit breakers should be marked or information should be provided to indicate the specific panelboards in which they can be installed. If the circuit breaker is not marked or the information is not provided, it is necessary to contact the circuit-breaker manufacturer. The manufacturer should be able to provide such information and it should be readily available.

As a general note, be aware that some circuit breakers are classified only and others are listed and classified. Generally, classified-only circuit breakers are limited to 15- and 20-amperes, 120/240-volts, and a maximum 10,000-ampere short-circuit current rating; they are intended for use in panelboards with a maximum 225-ampere rating. Although not obvious, there is a difference between listed and classified products.

Last, an article in Underwriters Laboratories The Code Authority, 2007 Issue 1, "Molded Case Circuit Breakers,” written by Warren Shilling, provides a good explanation for listed and classified circuit breakers. The article can be viewed at:http://www.ul.com/tca/issues/tca_issue_1_2007.pdf. — Lanny McMahill, CMP-1

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Tags:  Focus on the Code  January-February 2009 

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Exhaust Fans on Pitched Roofs

Posted By Lanny McMahill, Thursday, January 01, 2009
Updated: Monday, February 04, 2013

Question

The question I have is spread over several sections of the NEC (or so I think). I am inspecting a surgery center that has a 14-in-12 or, possibly, 16-in-12 pitch roof. The engineer wants to place an exhaust fan on this roof. I am finding nothing specifically in the NEC that would preclude the placement of an exhaust fan on this roof. If they build a working platform that meets the code requirements of space about electrical equipment and rent a crane to hoist a service tech to the location as the portable means, is this acceptable? I would like to say that none of this meets the requirements of the NEC (I am not one that likes to use AHJ) but have found nothing specifically that keeps them from doing this. The safety concerns and cost of having a man tethered to a crane just to change or service the motor is beyond my comprehension. It is just one fan motor on this roof. All other motors have been placed in the top floor penthouse. Is there anything in the NEC-2002 that can help me win this argument and prevent this motor from being placed on this roof? — J. C.

Answer

As you have noted, there is nothing in the National Electrical Code to preclude the installation of an exhaust fan on a roof — this is regardless of the roof being flat or pitched. Realistically, installing an exhaust fan on a roof is no different than if it were installed up high in an exterior building wall or down low in an underground vault.

An exhaust fan is electrical equipment. Section 110.26 requires that electrical equipment must have "sufficient access and working space” to "permit ready and safe operation and maintenance.” This section is a general requirement for all electrical equipment. The subsections that follow this section provide more specific requirements for access and working space. The more specific requirements are contingent on conditions that the equipment is "likely to require examination, adjustment, servicing or maintenance while energized.”

Do the general requirements apply to the exhaust fan? Generally, yes! What is considered "sufficient access” and "working space” is a judgment call for the authority having jurisdiction (AHJ). Naturally, a means must be available to reach the equipment and enough space must be available to work on the equipment — this is a general requirement. Sufficient access could be provided by a portable means, such as a ladder, lift or crane; sufficient working space could be provided by means of a platform or other structure. So, as with any electrical equipment, and depending on the intended purpose and function, generally sufficient access and working space must be available.

Do the specific requirements apply to the exhaust fan? Generally, no! For obvious safety reasons an exhaust fan should not be examined, adjusted or serviced while energized. An exhaust fan should always be disconnected from the power source before any type of work is performed. This should always be a standard safety practice. Since this is motor-operated equipment, Section 430.102(B) requires that a disconnecting means must "be located in sight from the motor location and driven machinery location.” It must also clearly indicate if it is in the open or closed position and must be readily accessible. The disconnecting means allows for the exhaust fan to be serviced in an electrically safe manner.

The "cost of having a man tethered to a crane just to change or service the motor” is not an NEC concern. This is something the design professional, installer and building owner should take into consideration. Fortunately, the cost of installing or servicing electrical equipment is not an enforcement issue.

Keep in mind that the purpose of the NEC "is the practical safeguarding of persons and property from hazards arising from the use of electricity. Practical safeguarding is a general statement too. Such statements require that the AHJ use good judgment, reason, logic and common sense in an enforcement practice. An exhaust fan on a roof is perhaps a good example of where such practice comes into play.

Although this may not be the response expected, hopefully it provides some guidance regarding your enforcement decision. — Lanny McMahill, CMP-1

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Tags:  Focus on the Code  January-February 2009 

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Is an additional bare copper bonding wire jumper required?

Posted By Michael Johnston, Monday, September 01, 2008
Updated: Monday, February 04, 2013

Question

Article 250.92(A)(2) of NEC-2005 requires bonding between service enclosures.

I have a meter base can with the grounding electrode conductor connected to the neutral lug going to the grounding electrode. I have a single-phase three-wire service conductor system feeding from the meter can to the service-disconnect panel. The meter base can and the service-disconnect panel is connected by PVC pipe, not metal pipe.

As I see it, Article 250.92(B)(1) allows bonding equipment (the service-disconnect panel) to the grounded service conductor neutral bar (in the service-disconnect panel). Is this correct, or is an additional bare copper bonding wire jumper required to be connected from the service-disconnect panel neutral bar to the meter base can neutral bar? — R. P.

Answer

Your question deals with use of the grounded conductor for grounding and bonding on the supply side of the service disconnecting means. Your understanding is correct. The grounding conductor is permitted to be used for grounding and bonding on the supply side of the service disconnecting means. The grounded (neutral) conductor is required to be routed between enclosures and bonded to both, and this is common practice. The supporting NEC references are 250.92(B)(1) and 250.142(A)(1).

An additional equipment bonding jumper between the meter socket enclosure and the service disconnecting means enclosure is not required for bonding the enclosures together based on the information provided in your question.

Note that on the load side of the service, disconnecting means (service disconnecting means overcurrent device), separation between the grounded (neutral) conductor is required in accordance with 250.24(A)(5). The grounding electrode conductor connection to the grounding electrode is permitted to be made in either the meter socket enclosure or the service disconnecting means enclosure in accordance with 250.24(A)(1).

Note that some utilities do not permit this connection in the meter socket enclosure by local regulations because of customer accessibility issues. I hope this helps answer your question. — Michael J. Johnston, CMP-5

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Tags:  Focus on the Code  September-October 2008 

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Size of bonding wire for 200-amp load center

Posted By Michael Johnston, Monday, September 01, 2008
Updated: Monday, February 04, 2013

Question

For a 200-amp load center used for feeding charging equipment that is approximately 400 ft from main switchboard, what size of bonding wire is required? — T. C.

Answer

The question appears to deal with a voltage-drop situation, but information is missing. I will answer the question by inserting the minimum necessary information. The first item to clarify is the terminology. I presume you are referring to the size of the equipment grounding conductor with the feeder and not a bonding wire which is undefined by the NEC. The next bit of information needed is the size of the ungrounded phase conductors intended to be installed for this feeder. Note: if a voltage-drop calculation is performed for this 400-ft feeder, then the system voltage and phase configuration of the feeder are necessary for the voltage-drop calculation. I will answer the question without the voltage-drop calculation information since this information is missing.

First, the question is restructured as follows:

What is the minimum size equipment grounding conductor required for a feeder (400 feet in length) supplying a panelboard for charging equipment?

For a 200-ampere feeder, a 3/0 copper conductor is generally required by the minimum requirements of the NEC. The minimum size equipment grounding conductor required for a 200-ampere feeder is not less than 6 AWG copper (see 250.122 and Table 250. 122). Now if the feeder ungrounded conductors have been increased in size from 3/0 copper to 250 kcmil copper (for example) for voltage drop reasons, then the required equipment grounding conductor must also be increased in size proportionately [see 250.122(B)]. This is done as follows using Table 8, chapter 9 of the NEC:

Using Table 8, Chapter 9
Required size 3/0 AWG = 167,800 cm
Adjusted size 250 kcmil = 250,000 cm

Adjusted size phase conductor ÷ Required phase conductor size = 250,000 ÷ 167,800 = 1.49
The multiplier is 1.49. The size of the ungrounded circuit conductors has been increased 149%; therefore, the equipment grounding conductors must be increased 149% as well, per 250.122(B).

Required equipment grounding conductor = 6 AWG copper (Table 250.122 based on 200 ampere overcurrent protection for the feeder)

Using Table 8, Chapter 9
6 AWG = 26,240 cm × 1.49 = 39,097.6 cm

According to Table 8, a 4 AWG copper is required = 41,740 cm

The minimum size equipment grounding conductor for this 200-ampere feeder is a 4 AWG copper conductor. The answer is based on NEC-2008, Sections 250.122, Table 250.122, and Chapter 9, Table 8 (conductor properties).

I hope this helps with you questions concerning sizing equipment grounding conductors for feeders. As always, consult the local authority having jurisdiction for any local electrical code rules that may be necessary in addition to the minimum requirements of the NEC. — Michael J. Johnston, CMP-5

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Tags:  Focus on the Code  September-October 2008 

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