Charlie Trout, author of Code FAQs and Code Question of the Day, has retired. Enjoy these highlights from his past responses.
Sealing conduit that passes into refrigerated room
Where can I find information in the National Electrical Code (NEC) detailing requirements for sealing conduit that passes from ambient temperature rooms into a refrigerated room? I know that condensation will form inside the raceway unless sealed.
NEC 300.7(A) requires that, where portions of a raceway are subjected to different temperatures and condensation is known to be a problem, the raceway must be filled with an approved material to prevent the circulation of warm air to a colder section of the raceway. An explosion-proof seal is not required for this purpose. Duct seal (electrical sealing putty) has been generally approved (90.4) for this purpose. Section: 300.7(A)
Neutral in each switch box?
We just failed inspection on a home rough-in and were told that each switch box had to have a neutral. This would mean installing cable with an additional insulated conductor for all switch loops run in the residence. The switches we are installing do not require a neutral connection to operate. Why do we have to install a neutral to each switch box?
Sounds like your inspection jurisdiction must have adopted the 2011 edition of the NEC. If that is the case, the inspector is correct. There is a new requirement to install a neutral (grounded conductor) in each switch box where the switch controls a lighting load. This was a significant change in the NEC that contractors and installers must be aware of to get right on the rough-in, as this applies to single-pole, three-way and four-way switches. It also applies to all occupancies, not just residential. The reason is related to all the electronic switches and devices that require a 120-volt (V) circuit to power the circuit board on the device. The equipment grounding conductor should not be used for this purpose as a current-carrying conductor. There are two exceptions to this rule that relax this requirement for the neutral. The first exception is for switch boxes installed using a raceway system where a neutral can be easily installed if needed in the future. The second exception is for installations where a cable assembly is accessible in a framing cavity open at the top or bottom on the same floor level, or where the cable is in a wall that is unfinished on one side, allowing access to the cable installation. On the other hand, cable assemblies are available with the additional insulated conductor to meet this requirement. Many quality NEC update classes are available to gain this knowledge of important Code changes that can be costly if one is unaware. I hope this is helpful, but it sounds like you have some more work to do before this rough wiring passes inspection. Section: 404.2(C) and Exception
Bushing for SER fitting
I have always requested an insulated bushing for SER cable connectors in the meter enclosure and service panel. I have recently been informed that the outer covering of the cable is not considered a raceway and that the inner surface of the connector is finished, so it does not require a bushing. Article 100 (raceways) includes a listing of various types but does not specifically state the category that the covering falls into.
Listed SER fittings provide a smoothly rounded surface to protect the conductors, and a bushing is not required. However, heavy conductors may tend to stress the conductors, and the use of an insulated bushing, while not required, may reduce the risk of insulation failure. Check 300.4(G), which applies to only raceways at this time, but logic would indicate a bushing should be installed to protect the conductors of a cable assembly from abrasion at the connector throat where it enters the cabinet or other enclosure. Section: 300.4(G)
When reading the Code on arc-fault circuit interrupters (AFCIs), I see the listed rooms that require AFCIs. Does that include lighting outlets or just receptacles? Also, do the rooms that are exceptions—such as bathrooms, kitchens, laundry and garages—need AFCIs on light outlets? Do other rooms such as storage, mechanical, workshop and exterior lights and plugs require AFCI protection?
NEC 210.12(A) requires all 15- and 20A circuits supplying outlets installed in those areas to be protected by a listed combination-type AFCI. Combination-type means capable of providing protection from both parallel and series type arc faults. The term outlets include both lighting and receptacle outlets. Only those rooms shown are required to be protected by an arc-fault circuit breaker. Section: 210.12(A)
Calculating ampacity of conductors
What is the ampacity of three 8 AWG XHHW conductors installed in a wet location with an ambient temperature of 45°C?
NEC Table 310.15(B)(16), formerly Table 310.16, shows the ampacity of an 8 AWG XHHW conductor to be 50 amperes (A) based on a temperature termination rating of 75°C and an ambient temperature of 30°C. The temperature correction factors are found in Table 310.15(B)(2)(A). For an ambient temperature or 40°C, multiply the ampere-carrying capacity by 0.95 in accordance with 110.14(C), resulting in 47.5A or 48A [220.5(B)].
Violating the NEC
A customer lost power on his home. Half the lights and plugs worked, but nothing 240V did. When I checked, I found that the main breaker had lost one leg. When I went to get a replacement breaker, it had to be ordered. Not wanting the homeowner to have to go without heat for three days (the amount of time they said it would take to get the breaker), I bolted lugs in the panel and hooked it up without overcurrent protection as a temporary fix. My question is what is your take on this solution? It actually only took two days, and I have since replaced the breaker. I have done service changes from 100A fuse boxes to 200A breaker panels, and I run a 6/2 Romex jumper between the two meters for temporary power until I get an inspection and the power company can run the new service. Inspectors are fine with this even though the 6 AWG is highly undersized.
The next time you obviously violate the requirements of the NEC and the inspector says it’s fine, write and tell me about it and be sure to have the inspector co-sign to verify his agreement. The only difference in a temporary power setup from a permanent power installation is typically in the wiring methods. All overcurrent protection, grounding, bonding, service, and other requirements should be followed; otherwise, it is an NEC violation. It also is important to get the authority having jurisdiction involved in these types of situations, which it sounds like you did. Sections: 230.90, 240.4, 240.21
Neutral in service disconnect
Is it required to install a neutral in the service disconnect even if there are no line-to-neutral loads? We have a 480V, three-phase, 3-wire, delta-connected system supplying the service disconnect, and there does not appear to be a grounded neutral conductor provided. The utility company says they would have to change the service drop to a 4-wire drop to accomplish this. The transformers on the pole appear to be wired in a wye configuration. What does the NEC require? We have step-down transformers installed on the load side of the service disconnecting means to produce 208Y/120V.
Where the service is supplied by an alternating current (AC) system that is grounded, the grounded conductor(s) must be routed with the ungrounded service conductors to each service disconnecting means and is required to be connected to each disconnecting means grounded conductor(s) terminal or bus. A main bonding jumper must connect the grounded conductor(s) to each service disconnecting means enclosure. There are no exceptions to this requirement, and it applies regardless of whether any line-to-neutral loads are supplied. The grounded conductor, usually a neutral, serves two functions. It carries any line-to-neutral current in normal operation, and it serves as the effective ground-fault current path to facilitate overcurrent device operation in the event of a ground fault on the system. It is a good idea to check with the serving utility to verify what type of system is being supplied and if it is grounded. Many utilities will no longer serve ungrounded systems under 600V.
The next time you obviously violate the requirements of the NEC and the inspector says it’s fine, tell me about it and be sure to have the inspector co-sign to verify his agreement.
Editor's Note: This is the last article in this series from Charlie Trout. We wish him the absolute best in his retirement. Stay tuned next month as James Dollard steps into Charlie's shoes as the new Code FAQs columnist.