Jim Dollard has an extensive background in codes and standards. If you have a query about the National Electrical Code (NEC), Jim will help you solve it. Questions can be sent to email@example.com. Answers are based on the 2014 NEC.
Multiwire branch circuits and outlet-type AFCIs
Can I wire arc-fault circuit interrupter (AFCI) outlets from two single-pole, 15-ampere (A) breakers with a shared neutral by wiring the receptacles beyond the shared neutral? My inspector is asking for documentation that the AFCI outlets can be used this way.
Yes. Based on your question, I assume the installation is in a dwelling unit on a single-phase, 120/240-volt (V) system. There are two issues to discuss. First, the installation is a multiwire branch circuit, and the NEC will require the two single-pole circuit breakers to be installed with an identified handle tie to facilitate simultaneous disconnection as Section 240.15(B)(2) requires. Second, the NEC does not specifically address the installation of outlet-branch-circuit-type or outlet-circuit-type AFCIs on a multiwire branch circuit. The answer here is driven by Section 110.3(B), which requires listed or labeled equipment to be installed and used in accordance with any listing or labeling instructions.
In this case, I believe the inspector’s concern is the ability of the outlet-type AFCI devices to function properly when supplied by a multiwire branch circuit. The 2015 UL White Book does not prohibit such an installation in any of the AFCI categories. The concern here may be generated due to requirements for AFCI circuit breakers supplying a multiwire branch circuit. The White Book clearly prohibits two-wire circuit breakers with ground-fault circuit interrupter (GFCI) or combination-type AFCI (DIYG) from being applied in a multiwire branch circuit as the NEC defines. Any type of device that will open where a ground fault occurs, such as a GFCI or combination-type AFCI circuit breaker, will not function properly when the device supplies a multiwire branch circuit. These devices measure the current supplied to the load and the current returning to the device to monitor current to ground and would constantly trip due to the common neutral (grounded) conductor. The NEC and applicable product standards permit supplying 125V, outlet-type AFCI receptacles from a multiwire branch circuit.
GFCI installation requirements in 70E?
In a recent electrical safety class, we learned that NFPA 70E now requires GFCI receptacles to be installed for maintenance and construction. Is this requirement in the NEC? If so, where?
NFPA 70E does not contain installation requirements. The requirements that you refer to are work-practice requirements located in Section 110.4(C)(2). These requirements are based on a “specified activity” of maintenance and construction, and they mirror federal regulations that require GFCI protection for personnel. The same requirement in Section 110.4(C)(1) mandates GFCI protection where other federal or local codes require.
GFCI installation requirements exist throughout the NEC, most notably in Section 210.8. The NEC contains GFCI requirements for temporary wiring used during construction, remodeling, maintenance, repair or demolition. In addition, the 1926 and 1910 standards contain GFCI requirements for personnel in federal Occupational Safety and Health Administration (OSHA) regulations for construction and general industry.
In many cases, these requirements do not require a GFCI-protected device to be installed. They require GFCI protection for personnel, and they permit a listed cord set or device that incorporates listed GFCI protection that is identified for “portable use.”
System grounding connection
The Code requires 208/120V services to be grounded. On a recent project, I installed a 200A temporary service on a construction site on a metal framing system 2 feet from the utility pole supplying the service. The utility visibly grounded the transformer secondary for the service 2 feet from the service equipment. We ran SE cable up the same pole the transformer is on to supply the service. The system is already grounded. Why do I still need to drive two ground rods?
Section 250.24 contains requirements for grounding service-supplied alternating-current (AC) systems. Section 250.24(A)(1) through (5) requires a grounding electrode conductor (GEC) to be connected to the grounded conductor at the service. In this case, the conductors from the utility-owned transformer to the service point are service-drop conductors. Section 250.24(A)(1) requires the GEC connection to be made on the load end of the service drop. Therefore, the Code permits the required connection to a grounding electrode to be made at any point downstream of where you spliced the SE cable to the service drop.
The NEC does not recognize a utility-installed conductor from the transformer to ground as a grounding electrode conductor. The NEC and the AHJ have no jurisdiction upstream of the service point. Without regard to how close they are to the utility transformer, all services must be grounded in accordance with the NEC. You are correct in that the utility has grounded the system. However, all NEC rules apply.
Tap 14 AWG on 20A circuit for switch legs?
We are installing lighting fixtures that come supplied with and require light-emitting diode (LED) lamps. The amount of current to supply these fixtures is extremely small. To provide an efficient, cost-effective installation for the homeowner, we use 14/2 Type nonmetallic (NM) cable for all of our switch legs in the home. Recently, an inspector cited us for this after the drywall was installed, and we had to replace those 20A circuit breakers with 15A circuit breakers to be compliant. Why does the NEC not permit this practice? Is the switch leg a fixture wire since it supplies the fixture?
The NEC prohibits using 14 AWG copper conductors for switch legs on a branch circuit protected at 20A. Conductors are required to be protected at their rated ampacity. There are specific “tap rules” that, under specific conditions, will permit smaller conductors; however, using smaller conductors for switch legs is not permitted. As Section 240.4(D) states, the general rule for 14 AWG copper overcurrent protection is to not exceed 15A. Provisions in 240.4(E) recognize tap rules in 210.19(A)(3) and (A)(4) for ranges and cooking appliances and 240.5(B)(2) for fixture wire, but these permissive requirements do not apply to switch legs. Article 402 contains requirements for fixture wires and lists all types of fixture wires in Table 402.3. Switch-leg conductors are typically installed in a raceway or cable assembly with conductor types listed in Table 310.15(B)(16) and are not fixture wires.
When applying the rules from Section 110.26(C)(2)(a), a single entrance and egress is permitted where there is unobstructed egress. We have a situation where a switchboard around 16 feet wide needs to meet Section 110.26(C)(2)(a) requirements, but there is a break in the wall toward the exit door that removes a direct path from one end of the switchboard to the exit. Due to this building’s equipment layout, the only possible additional exit would be right next to the single exit as designed. What is meant by unobstructed?
You have captured the meaning of unobstructed in your question. To exit a room, if you need to step around or over any obstacle—such as a wall, transformer or other equipment—from within the working space footprint that Section 110.26(A) requires, your egress path is obstructed. The general rule in Section 110.26(C)(2) is for two means of access and egress (entrances) with one at each end of the working space. Note that there is no mention in this unobstructed path requirement. In this case, I suggest you confer with the authority having jurisdiction (AHJ) and designer to determine a compliant solution. One example is to ensure that there is extra working space as permitted in Section 110.26(C)(2)(b).
Equipotential plane at service equipment?
The bid drawings for a highway project require an equipotential plane for multiple small services that supply equipment for stormwater retention basin systems. Is this an NEC requirement or a design requirement?
It is an NEC requirement. In this case, refer to Article 682, Natural and Artificial Made Bodies of Water. Section 682.33 requires an equipotential plane to mitigate step and touch voltages at electrical equipment. An equipotential plane is required for service equipment with a metallic enclosure, and it must encompass the area around the service equipment and extend from the area directly below the service equipment a minimum of 3 feet in all directions from which a person would be able to stand and come in contact with the equipment.