Code Q&A by Mike Holt

[Following is reprinted from Mike Holt's Newsletter]
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Q1. A main lug only distribution panel is fed through an automatic transfer switch. The automatic transfer switch, the generator, and normal power are all located remotely from the distribution panel. I was told that the distribution panel does not require a main circuit breaker (disconnect). I contend that in order to disconnect the power to the distribution panel, you have to open both the normal and generator circuit breakers (cannot be disconnected by a single breaker). Therefore a main breaker (disconnect) is required to be installed "in" the disruption panel, but I cannot support this with a specific NEC rule. Am I right?

A1. No. Section 384-16(a) does not require a disconnecting means for a panelboard. But it does require panelboard with a neutral that has more than 10 percent of its overcurrent devices rated 30 amperes or less to be protected against overcurrent by a device that has a rating not greater than that of the panelboard. Exception No. 1 to this rule states that the overcurrent protection is not required to be located in the panelboard, if the panelboard feeder has overcurrent protection not greater than the rating of the panelboard. In your case if the panelboard has proper overcurrent protection, the installation meets the NEC requirements.

As. Yes. Section 373-8 states that enclosures for overcurrent devices shall not be used as a junction box or raceways, unless adequate space is provided. Conductors inside a panelboard shall not fill the wiring space at any cross section to more than 40 percent, and splices and taps shall not fill the wiring space at any cross section to more than 75 percent, Figure 1.

Q3. How do I ground a transformer in a building where there is no accessible effectively grounded structural metal member of the structure and effectively grounded metal water pipe is a over 200 feet from the transformer?

A3. Drive a ground rod. Section 250-30(a)(2) requires a grounding electrode conductor to connect the grounded (neutral) conductor of the transformer to a grounding electrode. Section 250-30(a)(3) requires the grounding electrode to be as near as practicable and preferably in the same area as transformer. Where effectively grounded structural metal member of the structure or effectively grounded metal water pipe within 5 ft from the point of entrance into the building is not available, then a ground rod installed in accordance with the requirements of Sections 250-52 can be used.

Q4. I have encountered a design specification, which states: "Pull points shall be provided in each conduit run to conform with the requirements of the NEC ". I have always installed "pull boxes" 100 feet from each other. I tried looking this up in the Code but was unable to find anything in reference to the distance between pull boxes. Is there any rule in the NEC that pertains to this?

A4. No. The NEC does NOT contain any requirement limiting the distance between pull points. Conductors cannot be spliced within a raceway [300-13(a)], so the maximum distance between pull boxes is dependent on the length of the conductors.

The Code specifies (this is contained in each of the raceway articles) that there shall not be more than the equivalent of four-quarter bends (360 degrees total) between pull points. In addition, the Code also alerts us to the fact that “raceway fill” is based on common conditions where the length of the pull and the number of bends are within reasonable limits. It states that for certain conditions, a larger size conduit or a lesser conduit fill should be considered [FPN to Table 1 of Chapter 9].

Q5. I recently had an electrical inspector require a 75-kVA transformer be removed from a drop ceiling grid area. He claims that the Code does not allow a 75-kVA transformer to be installed above a suspended ceiling. Our position is that this is not a Code violation if the transformer complied with all the clearance, access and ventilation requirements of the Code. Does the Code allow a 75-kVA transformer to be installed above a drop ceiling grid area?

A5. No. The general requirement of Section 450-13 is that transformers must be readily accessible to qualified personnel for inspection and maintenance. However, dry-type transformers rated not over 600 volts and not over 50 kVA, can be located above a suspended ceiling (not readily accessible), if not permanently closed in by structure and provided they meet the ventilation requirements of Section 450-9 and separation from combustible materials requirements of Section 450-21(a) [450-3(b)]. Since your transformer is greater than 50 kVA (75 kVA), it cannot be installed above the suspended ceiling space because it is not readily accessible, Figure 2.

Q6. What is the maximum size hole an electrician can drill in a ten-inch floor joist? I have been in commercial construction most of my life and always left the structural supports intact. When having a house built I was surprised to see a four-inch hole cut into the two outside joists for an exhaust fan. I do not believe there was any harm done to my structure, but does the NEC cover this?

Q7. For purposes of computing the lighting load for feeders and services, many engineering firms in our geographical area disregard Table 220-3(a), and instead use 125% of the actual installed lighting load. When the bulk of the light fixtures employ T8 fluorescent lamps with electronic ballasts, such a computation results in a lower load than Table 220-3(a) would require. Does the National Electrical Code permit this?

A7. No. Section 220-3(a) is very clear in that it states that the “lighting load of not less than that specified in Table 220-3(a) shall constitute the minimum lighting load for each square foot of floor area”. Example D3 in Appendix D contains a note that clarifies that “where the actual connected lighting load (at 125%) is less than 125% of the load from Table 220-3(a), “the minimum lighting load from Table 220-3(a) shall be used in the calculation. Had the actual lighting load been greater than the value computed from Table 220-3(a), 125% of the actual connected lighting load would have been used.”

Q8. I am confused as to how to size the neutral conductor for commercial service and feeder conductors. Am I required to size the neutral conductor at 125% for continuous loads?

A8. Yes. NEC Section 215-2 for feeders and Section 230-42 for services require the ampacity of the conductors (before the application of any adjustment or correction factors) to have an ampacity of not less than 125 percent of continuous loads, plus the sum of noncontinuous load. Since the neutral (grounded) conductor is part of the feeder or service, it must also comply with the same requirements, therefore the neutral must be sized not less than 125 percent of continuous loads, plus the sum of noncontinuous load in accordance with Section 220-22.

Example: If the load on the feeder/service consisted of 150 amperes of three-phase 208 volt loads and 150 amperes of single-phase 120 volt loads, the feeder/service conductors would be, 3 500 kcmil and 1 No. 3/0.

Q9a. We recently moved a large circuit breaker for some heavy industrial equipment. Now the load conductors will not reach the bottom of the circuit breakers. The customer wants us to back-feed the circuit breaker (line conductors terminate on the bottom of the breaker and the load conductors terminate to the top of the breaker) instead of running new (and expensive) wire. The manufacturer of the heavy industrial equipment insists that we can connect the line or load to either side of the circuit breaker. However, many of electrical people here at the facility feel that the NEC requires the supply to terminate to the top terminals and the load to terminate to the bottom terminals. I haven't been able to find this regulation in the NEC.

Q9b. I have a question regarding the proper connection to a circuit breaker and I can't find anyone who will make a statement with confidence or who can steer me in the right direction. I understand that it is common practice to connect the line side to the top of the breaker and the load side to the bottom of the breaker. I was also told that an inspector always assumes that the breakers are wired this way. However, if you have an underground service entering a CT cabinet and where the main breaker is located directly above the CT cabinet, why must you still wire the line side to the top of the breaker? In this situation, it is obvious where the line side originates. Doesn't the breaker function the same way whether it is fed from the top or the bottom? Does the NEC cover this?

A9. Yes. NEC Section 110-3(b) states “Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.” According to Underwriters Laboratories Inc. (UL) “General Information Directory,” breakers that are marked “Line and Load” are intended to be wired so that the supply (line) terminates to the “Line” terminal and the feed (load) terminates to the “Load” terminal. Circuit breakers that do not have “Line and Load markings can be wired in either direction, Figure 3.

Q10. I installed a panel on the wall of a bathroom of a commercial building, where the distance from the front of the panel to the toilet is 5 feet. My question is, is it legal to install a panel in a commercial bathroom?

A10. Yes. Section 240-24(e) only prohibits overcurrent devices in bathrooms* of dwelling units and guest rooms of hotels and motels. Since this is not a residential bathroom, the installation of the panel in the bathroom is permitted. Careful, Section 230-70 prohibits the installation of the service disconnecting in any bathroom.

Q11. My question is about the use of 3” pancake boxes (½” deep). It seems to me as that there is not enough volume in the box to handle a light fixture connection consisting of a hot, neutral, and a ground. Does the canopy of the light fixture have any effect when calculating volume requirements?

A11. Yes. Section 370-16(b)(1) Exception states that equipment grounding conductor and not over four fixture wires smaller than No. 14 are not required to be counted when they enter a box from a domed fixture, Figure 4.

Q12. NEC Section 250-56 states, “A single electrode consisting of a rod, pipe, or plate that does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode.” How do you determine if the electrode meets this requirement, and why don't inspectors require testing of grounding electrodes.

A12. The resistance of a ground rod can be determined by using the “fall of potential method”. For more information visit http://www.mikeholt.com/Newsletters/GroundResistance.htm. There is no need for an inspector to measure the resistance of the ground rod, if there are two ground rods installed in accordance with Sections 250-52 and 250-56.

A13. Maybe. This is a judgment call by the inspector. Section 240-24(d) prohibits overcurrent devices (circuit breakers) from be located in the vicinity of easily ignitible material, “such as in clothes closets”. To me the key is “easily ignitible materials”, but my experience is that most inspectors focus on “such as in clothes closets” and will probably prohibit this installation.

Q14. If a wraparound style fluorescent fixture is secured to a T-bar ceiling, can you run a cord out the top of the fixture to a receptacle located in the ceiling area, if the ceiling space is not used as a plenum area in an office space?

A14. Maybe. Section 410-14(a) permits electric-discharge lighting fixtures supported independent of the outlet box to be connected to the branch circuit by flexible cord if:

2. The fixture is located directly below the outlet box and the flexible cord is visible for its entire length outside the fixture, and the cord is not subject to strain or physical damage [410-41(c)].

A15. No. Telecommunications systems [800-40(b)], antennas and lead-in cables [810-21(f)], CATV [820-40(b)], and network-powered broadband communications systems [830-40(b)] must all be bonded to one of the following locations Figure 5:

Mike's Comment: When a ground rod is installed for a communications system (your question), it must be bonded with a No. 6 copper or larger bare or insulated conductor to the grounding electrode system at the building or structure served.

Q16. Does the Code allow Class 2 low voltage cable (CL2) to be run exposed in occupied public space? Can the cable be run exposed in a non-public workspace, i.e. mechanical room, etc.?

A16. Maybe. Section 725-7, which covers mechanical execution of work, specifies that Class 1, Class 2, and Class 3 circuits shall be supported by the building structure in such a manner that the cable “will not be damaged by normal building use”. Cables installed in public places where they could be damaged by normal building use would have to be protected or installed in a suitable raceway.

Cables installed in mechanical rooms where they could be damaged by normal building use would also have to be protected or installed in a suitable raceway. The bottom line is that this is a judgment call by the “authority having jurisdiction”, which is usually the electrical inspector.

A17. Yes. There is no NEC rule on the separation of underground raceways or cables from other piping systems. However, underground conductors for satellite dishes and antenna [810-18(a)], direct-buried coaxial cable [820-11(b)], and network-powered broadband communications cables shall be separated at least 12 in. from conductors of any light or power circuits.

Q18. My local inspector believes the bending radius on 500 kcmil conductors entering the back of a 6 inch deep enclosure was violated. The inspector passed the installation but said he would not the next time. Can a 6 inch deep enclosure, such as a panel cabinet be used for 500 kcmil conductors entering the back of the enclosure?

A18. Yes. Conductors shall not be deflected (bent) within a cabinet or cutout box unless sufficient width (in this case dept) is provided in accordance with Table 373-6(a). Table 373-6(a) required a minimum of 6 inches of width (depth) in the cabinet so that 500 kcmil conductors can be properly deflected (bent), Figure 6.

Q19. A 230 volts central air conditioning specifies a maximum 45-ampere fuse or HACR breaker, with a minimum circuit ampacity of 27.8 amps. Can I use No. 10 THHN with a 40-ampere HACR Breaker?

Conductors Sizing Section 440-33. Conductors supplying a motor-compressor with additional load(s) shall have an ampacity not less 125 percent of the highest motor or motor-compressor rating in the group, plus the other loads.

Protection Sizing Section 440-22(b). The protective device having a rating or setting not exceeding 175% of the largest motor-compressor rated-load current, plus the other loads, shall be permitted. Where the protection at 175% is not sufficient for the starting current of the motor, the protection rating can be increased to 225% of the largest motor-compressor rated-load current, plus the other loads.

Ground Rod/Plate Electrode [250-66(a)]. Where the grounding electrode conductor is connected to a ground rod or plate electrode [250-52(c)(d)], that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than No. 6 copper wire.

Concrete-Encased Electrodes [250-66(b)]. Where the grounding electrode conductor is connected to a concrete-encased electrode [250-50(c)], that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than No. 4 copper wire.

Ground Rings [250-66(c)]. Where the grounding electrode conductor is connected to a ground ring [250-50(d)], that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than the conductor used for the ground ring.

Other Electrodes. Where the grounding electrode conductor is connected to any other electrode [250-50], the conductor shall not be less than given in Table 250-66.

So the answer depends on the electrode. It would not have to be larger than No. 6 copper to a ground rod, No. 4 copper to concrete-encased steel (Ufer), No. 2 copper to a ground ring, or No. 3/0 copper for all other electrodes.

Q21. I'm installing a feeder in parallel. Can I use to different types of insulation on the different phases? Example: A phase - THHN, B phase - XHHW, and C phase - THHN.

A21. Yes. Section 310-4. When conductors are run in parallel (joined together at both ends electrically, thereby forming a single electrical conductor), the currents need to be evenly divided between the individual parallel conductors so that each conductor is evenly heated. This is accomplished by ensuring that each of the conductors within a parallel set has the same impedance, material, cross-sectional area, and insulation type, and that all conductors terminate in the same manner.

The FPN to this Section in the 1996 NEC indicated that conductors of one phase or grounded (neutral) conductor were not required to have the same physical characteristics as those of another phase or grounded (neutral) conductor to achieve even current distribution. In the 1999 NEC, this text was relocated from the FPN into a positive Code requirement for Section 310-4.

A22. No, No. The NEC does not require a separate circuit for a refrigerator. Section 210-23(a) allows a refrigerator (or any appliance) to be on a 15 or 20 ampere circuit with other loads if the appliance does not exceed 50 percent of the branch-circuit rating. Section 210-52(b)(1) identifies that the 20 ampere small appliance circuit for a dwelling unit can supply refrigeration equipment, but only if the refrigerator does not exceed 50% of the small appliance circuit rating in accordance with Section 210-23(a).

A23. No. Flexible wiring methods are used for installation convenience, reduction of audible noise from vibration, and where flexibility is required. Generally a flexible wiring method is used for the primary and secondary supply for a transformer, because is much easier to install flex then EMT or PVC. However, electrical metallic tubing, rigid nonmetallic conduit, or any other fixed raceway could be use for the transformer primary or secondary supply, Figure 9.

Q24. I'm terminating No. 14 THHN stranded wire to a circuit breaker. One of the electricians on the job said that terminating stranded wire to a breaker was a Code violation and a fork connector was required whenever we terminate stranded No. 14 or No. 12 wire. Is this true?

A25. No. The NEC only requires that a switch not be installed within the wet location of a tub or shower spaces, unless the switch is part of a listed tub or shower assembly, Figure 10.