If you have a problem related to the National Electrical Code (NEC), are experiencing difficulty in understanding a Code requirement, or are wondering why or if such a requirement exists, ask Charlie, and he will let the Code decide. Questions can be sent to email@example.com. Answers to questions are based on the 2011 NEC.
Disconnecting four-gang box
The first question in your February 2011 article is a good one. It regards de-energizing both legs in an electrical box when they both are not connected to the outlet. Most everyone understands that both legs connected to the same returning neutral need to be de-energized by breakers with tied handles. This question goes a bit further and asks, if there are four individually breakered circuits in one four-gang box—say, with four outlets in it—would all the circuit breakers’ handles need to be tied together so that everything in the box would turn off at the same time?
OK, let’s try it again. NEC 210.4(B) requires that each multiwire branch circuit be provided with a means to simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates. This means that a multipole breaker or breakers tied together with handle ties must be used to supply multiwire branch circuits. The purpose of this requirement is to reduce the risk of shock to those working on equipment supplied by a multiwire branch circuit by disconnecting the entire multiwire branch circuit supplying the equipment. Simultaneous disconnection is required where a neutral conductor is shared by two or more phase conductors. As to the question concerning a four-gang box with four outlets, I presume you mean receptacle outlets, with each on its own circuit. Simultaneous disconnection would only be required for those circuits sharing the same neutral and those required by 210.7 for any multiple circuits supplying devices or equipment on the same yoke.
Sizing grounding-electrode conductors
What size grounding-electrode conductor should be used for service panels requiring 4/0 or larger copper wire where the grounding-electrode conductor is connected to a concrete-encased electrode and a metal water pipe?
NEC 250.50 requires that, where present, the metal underground water pipe and the concrete-encased electrode shown in 250.52(A)(1) and (3) be bonded together to form the grounding-electrode system. This can be accomplished by installing a 4 AWG grounding-electrode conductor to the concrete-encased electrode [250.66(B)] and a 2 AWG to the metal water pipe (250.66). You are permitted, however, to run a 2 AWG to the metal water pipe and bond the concrete-encased electrode to the water pipe using a 4 AWG bonding conductor. If you run to the concrete-encased electrode first and then bond the metal water pipe to it, you must run a 2 AWG the entire length to maintain the proper conductor size to the metal water pipe.
Purpose of new article
What is the purpose of 210.7?
NEC 210.7 is new in the 2011 Code. Its purpose is to provide safety by requiring simultaneous disconnection where multiple circuits supply devices on a common yoke. Multiple circuits in 210.7 means more than one circuit, on separate phases, each with its own neutral as opposed to a multiwire circuit where a neutral is shared. The reason I specify “on separate phases” is that simultaneous disconnection would not be possible if the multiple circuits were on the same phase.
Is neutral current-carrying?
In March 2011, you state the neutral wire is not a current-carrying conductor and does not need to be counted for derating purposes. The question states that the fourth wire is a neutral. Please explain how a neutral carrying the unbalanced load is not a current-carrying conductor. I have never had an instructor or inspector who did not consider the neutral a current-carrying conductor.
Of course the neutral is a current-carrying conductor. However, it carries only the unbalanced current from the other conductors of the same-circuit. For this reason, it is not counted as a current-carrying conductor when applying the provisions of 310.15(B)(3)(a). In the March issue, I stated “but only the three-phase conductors are considered as being current-carrying,” and I see no problem with that.
Encasement of service laterals
When is concrete encasement of service laterals required when inside a building?
To be considered as being outside the building where installed within a building, 230.6(2) requires encasement in concrete or brick not less than 2 inches thick.
Are travelers for three-way and four-way switches to be counted when calculating ampacity correction conduit wire fill?
Travelers are required to be counted when calculating conduit fill but not for applying the provisions of Table 310.15(B)(3)(a) for ampacity-adjustment factors.
Unsafe back-wired receptacles
When will the NEC require manufacturers to stop making receptacles that can be back-wired (wires pushed in from the back instead of wires tightened under the screws)? We have seen too many very badly burned receptacles, outlet boxes, and even mattresses due to failing connections in back-wired receptacles. If the NEC is truly interested in life-safety issues, eliminating the possibility of back-wiring a receptacle should be a priority.
If a proposal is submitted to the National Fire Protection Agency (NFPA) in proper form with definitive substantiation showing the need for acceptance of the proposal, the Code-Making Panel (in this instance, CMP-18) will review the substantiation and decide whether to reject or accept the proposal in some form.
Service equipment marking
Why are some panelboards marked “Suitable Only For Use As Service Equipment” while others are marked “Suitable For Use As Service Equipment”?
Panelboards with the neutral bar-factory-bonded to the frame or enclosure are marked “Suitable Only For Use As Service Equipment.” Panelboards incorporating provisions for bonding the neutral bar to the frame or enclosure in the field are marked “Suitable For Use As Service Equipment.”
Splitting countertop receptacles
Are countertop receptacles required to be split so that we have two circuits at each receptacle outlet?
No. Section 210-52(b)(3) requires that receptacles installed to serve countertop spaces shall be supplied by not less than two small-appliance branch circuits. These two circuits can be the same ones that supply other outlets in the kitchen, pantry, breakfast room, dining room and similar areas of the dwelling unit. All that is required is to have countertop receptacles supplied by two small-appliance branch circuits. You can use the two circuits by splitting receptacles, you can alternate receptacles, or you can put a single receptacle on one circuit and all the rest on the other circuit. Remember, you are not limited to two small-appliance branch circuits in the dwelling unit.
Neon sign above drywall ceiling
Can I locate the ballast for a neon sign above the drywall ceiling of the show window where the sign is located?
Yes, assuming there is access to the area above the ceiling and that you comply with Sections 600.21(E). Where the secondary conductors pass through the ceiling, be sure to follow Section 600.32.
What is meant by the term “series rated”?
A circuit breaker can be used on a circuit having an available fault current higher than its marked interrupting rating if it is connected on the load side of an acceptable overcurrent device having the higher rating. For example, if a service panel had 14,000A of available fault current at its terminals, circuit breakers marked 10,000A could be used if the main breaker was marked 22,000A. If a fault occurs on the load side of a branch breaker, then the main breaker and the branch breaker act “in series,” and both trip “off.” Section 240.86 has additional information relating to series ratings.
TROUT answers the Code Question of the Day on the NECA website. He can be reached at firstname.lastname@example.org.