NEC Questions and Answers Based on the 2008 NEC
June – Part 1

By Mike Holt for EC&M Magazine, http://ecmweb.com/

Here’s the follow up to yesterday’s newsletter. This includes all of the answers to the questions sent yesterday, so you can see how you did.

Q1. What are the rules regarding electrical raceways and cables near gas piping?
A1. There aren’t any rules in the NEC that cover this, so you can put them as close as you would like.

Q2. I recently saw a circuit breaker that was locked in the “on” position. Is this a Code violation? It sure seems like it should be.
A2. It may look odd, but there is nothing in the Code that says you can’t do this. In fact, if you use the exception to 700.12(F), the Code requires the breaker to be locked on. This is safe because breakers are required to “trip free,” meaning that they will trip internally under an overcurrent condition, even if the handle is locked “on”.

Q3. What is the length of raceway where the conductor ampacity is not required to be adjusted for conductor bundling?
A3. The conductor ampacity adjustment factors of Table 310.15(B)(2)(a) don’t apply to conductors installed in raceways not exceeding 24 in. in length [310.15(B)(2)(a) Ex No. 2].

Q4. Is it legal to splice conductors in an “LB” fitting?
A4. Splices are only permitted in conduit bodies that are marked by the manufacturer with their volume; and the maximum number of conductors permitted in a conduit body is limited in accordance with 314.16(B) [314.16(C)(2)].
Example:: How many 12 AWG conductors can be spliced in a conduit body that has a capacity of 15 cu in.?
(a) 4              (b) 6             (c) 8           (d) 10
Answer: (b) 6 conductors (15 cu in./2.25 cu in.)
12 AWG = 2.25 cu in. [Table 314.16(B)]
15 cu in./2.25 cu in. = 6 conductors

Note: Short-radius conduit bodies, such as capped elbows, handy ells, and service-entrance elbows must not contain any splices or taps [314.5].
 
Q5. We have a line voltage fire alarm system in a commercial building. I thought it was illegal to install the supply conductors with the signaling conductors (120V) in the same raceway.
A5. Power-supply and fire alarm circuit conductors are only allowed in the same cable, enclosure, or raceway where they are connected to the same equipment [760.48(B)].

Q6. How do you properly size a generator? Is there a standard somewhere that provides any guidance?
A6. Prior to the 2008 NEC, the Code was silent on requiring any types of calculations for optional standby systems. New to the Code in the 2008 edition is 702.5(B)(2) which tells us that the optional standby power source must have adequate capacity to supply the full load transferred, if using an automatic transfer switch.

For a new installation, the load is determined by Article 220 or an alternate method approved by the AHJ. For existing facilities, the maximum demand data for 1 year or the average power demand of a 15-minute period over a minimum of 30 days can be used to size the power source [220.87].

Q7. For a 240V to 208Y/120V transformer, is it better to bond the neutral to the metal frame at the transformer itself, at the panel, or at both locations?
A7. A system bonding jumper must be installed at the same location where the grounding electrode conductor terminates to the neutral terminal of the transformer. This connection can be either at the transformer or the system disconnecting means, but not at both locations [250.30(A)(1) and (A)(3)].

Q8. Does the Code address sharing a neutral for two conductors of the same phase?
A8. Well, not really. 310.10 is the closest thing you will find, which says conductors must not be used where the operating temperature exceeds that designated for the type of insulated conductor involved. With that said, it would be legal to do this if the neutral was big enough.

Q9. I was written up for having my NM cable in the same drilled stud hole as my doorbell wiring. I have been doing this for years…have I been wrong all this time?
A9. No, you haven’t been doing it wrong. The section you were probably cited was 725.136(A), which states “Class 2 and Class 3 circuit conductors and cables must not be placed in any enclosure, raceway, or cable with conductors of electric light, power, and Class 1 circuits.” Notice that this rule applies to conductors of electric light and power, not cables of electric light and power.

Q10. Does the Code specify a maximum length for a disposal cord?
A10. Yes. A flexible cord is permitted for a waste disposal if the cord has a grounding-type attachment plug, the cord length is at least 18 in. and not longer than 3 ft, the waste disposal receptacle is located to avoid damage to the cord, and the waste disposal receptacle is accessible [422.16(B)(1)].

Q11. We typically put the refrigerator for a house on its own circuit, but do I have to do this for commercial as well? These are very small refrigerators, if it makes any difference.
A11.There is nothing that requires a refrigerator to be on an individual branch circuit, either for residential or commercial applications.

Q12. Can I install a panel in the clothes closet of a house if the working space of 110.26 is maintained?
A12. No, Overcurrent devices are not permitted to be located near easily ignitible material, such as in clothes closets. Figure 240–30
Author’s Comment: The purpose of keeping overcurrent devices away from easily ignitible material is to prevent fires, not to keep them out of clothes closets.

Q13. We do a lot of generators for residences, and only recently have been getting written up on our transfer switches. The inspectors are saying that if I use the transfer switch to transfer the entire house, and I put it between the meter and the service disconnect, then the transfer switch must be “service rated.” Can you help me understand the rules please?
A13. There are a couple of rules that have to be followed that ultimately get you to what your inspector is saying. In general, electrical equipment must not be connected to the supply side of the service disconnect enclosure, which means that transfer equipment can’t be on the supply side of the service disconnect [230.82.]. Therefore, you must make your transfer switch your service disconnect; in order to do that, it must be listed as “suitable for use as service equipment” [230.66].