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. Send questions to firstname.lastname@example.org. Answers are based on the 2017 NEC.
Supply 240V equipment at 208V?
Is it permissible to supply cord-and-plug-connected equipment rated at 120/240 volts (V) from a 208/120V system? The owner had problems with some equipment and asked us to find out why. The cord-and-plug connections are 240V, which confused us at first.
No, this installation is not NEC-compliant. This is a violation of 110.3(B), which requires listed or labeled equipment to be installed in accordance with any instructions included in the listing or labeling. The electrical equipment supplied, the male cord caps and associated receptacles must be installed in accordance with their listing and labeling. This also violates 110.4, which requires the voltage rating of electrical equipment to be not less than the nominal voltage of the circuit to which it is connected. While this installation did not likely involve a marina or boatyard, there is an informational note (IN) in Article 555 that is very helpful here. See the IN that follows 555.19(A)(3) for branch circuits supplying shore power receptacles. It explains that, where receptacles are supplied at voltages other than that marked on the receptacle, overheating or malfunctioning of the connected equipment may occur.
Receptacle replacement, knob and tube
In our area, a significant number of older homes are still wired with knob and tube, which means combined neutrals throughout the home. Replacing old two-wire, nongrounding receptacles is going to become a significant challenge now that we have adopted new editions of the NEC. We are getting completely different interpretations based upon the township we are discussing this with. In some areas, we are told we can replace the old devices with dual-function receptacles and protect others downstream. In another township, we have been told to comply with 210.12(D) because we are modifying the circuit. What is required? Just 406.4(D)? Where does 210.12(D) apply?
In your question, you refer to the adoption of new NEC editions. My response is based on the 2017 NEC.
We must first determine if 210.12(D) applies. The requirements of 210.12(D) do not affect the replacement of receptacles of any type in an existing dwelling unit. This requirement applies only where branch circuit wiring is modified, replaced or extended. Where this occurs, the branch circuit must be protected by one of two methods: (1) a listed combination-type arc flash circuit interrupter (AFCI) at the origin of the branch circuit (which must be a circuit breaker because that is where the branch circuit begins) or (2) a listed outlet branch-circuit-type AFCI located at the first receptacle outlet of the existing branch circuit.
There is an exception to this requirement that applies where the extension of existing conductors is not more than 6 feet and does not include additional outlets or devices. As you are not adding additional outlets or devices and are not extending the branch circuit, this requirement does not apply in this case. However, the requirements of 406.4(D) do apply. AFCI protection of receptacle replacements will be required by 406.4(D)(4) for all receptacles replaced in areas identified in 210.12(A) and (B). This protection is permitted to be (1) a listed outlet branch-circuit-type AFCI receptacle, (2) a receptacle protected by a listed outlet branch-circuit type AFCI receptacle or (3) a receptacle protected by a listed combination-type AFCI circuit breaker. Where the replacement receptacles are nongrounding-type receptacles as permitted by 406.4(D)(2)(a) and are not in locations that require GFCI protection as per 210.8, all that is needed is a listed combination-type AFCI circuit breaker or an outlet branch-circuit-type AFCI protecting the replacement receptacles. These devices are not required to provide ground fault protection whether it be at GFCI or ground fault protection (GFP) levels and will function properly whether or not shared neutrals exist downstream.
It is important to note that some devices may have a GFP/GFCI component. It was a common practice to combine neutral conductors throughout the dwelling unit in knob-and-tube wiring, so devices (circuit breakers or receptacles) that use GFP or GFCI technology will open when multiple loads are turned on due to the fact that not all of the current will return over one neutral conductor. That means dual-function devices and AFCI devices that have a GFP component may not work well with knob-and-tube wiring. Different types of AFCI technology are available for use in these applications, and it is imperative to contact the AFCI circuit breaker or receptacle manufacturer to determine the best solution. Homeowners typically desire the replacement device to be a three-wire receptacle including an equipment grounding conductor connection.
Since equipment grounding conductors do not typically exist in dwelling units wired with knob and tube, replacement devices must comply with 406.4(D)(2)(b) or (c), requiring GFCI protection in addition to AFCI protection. This will require one of the following: (1) dual-function receptacles or circuit breakers, (2) a combination of an AFCI circuit breaker and a GFCI receptacle, or (3) a combination of a GFCI circuit breaker and an outlet branch-circuit type AFCI receptacle. Shared neutrals will have to be addressed either at the panelboard through the use of two-pole AFCI/GFCI dual-function circuit breakers or at the locations where the shared neutrals exist.
It is important to note that, where installed, AFCI, GFCI or dual-function circuit breakers and receptacles must be readily accessible. The exception to 406.4(D)(4) is no longer relevant. This exception permitted AFCI protection to be omitted where the installation complied with four list items. Listed combination type AFCI circuit breakers and GFCI/AFCI dual-function receptacles are now commercially available, which means this exception cannot be applied.
Parallel feeders in wireway
When installing parallel feeders in a wireway, are the number of current-carrying conductors determined in the same manner as we do for branch circuits?
The general requirement in 310.15(B)(3)(a) applies where the number of current-arrying conductors exceeds three and each conductor of a paralleled set of conductors must be counted as a current-carrying conductor. Section 376.22(B) modifies 310.15(B)(3)(a) requirements, and the adjustment factors apply only where the number of current-carrying conductors exceeds 30 at any wireway cross-section. It is important to note that, when calculating the number of current-carrying conductors, we must include all spare conductors. See the note to Table 310.15(B)(3)(a).
Additionally, the requirements of 376.20 apply where feeders are installed in parallel in a wireway. This requires separating the paralleled feeder into groups consisting of not more than one conductor per phase, neutral or grounded conductor to prevent current imbalance in the parallel conductors due to inductive reactance. This can be achieved through using cable ties or other methods.
Insulated service conductors
We recently replaced a service and found the neutral was uninsulated copper installed in rigid conduit. Is that permitted? I have always been under the impression that, in a service, the only time bare neutrals are permitted is in service entrance cable.
The general rule in Section 230.41 is all service entrance conductors entering or on the exterior of buildings or structures must be insulated. An exception lists five scenarios where a grounded service conductor is permitted to be uninsulated. List item (1) permits bare copper in a raceway or service cable assembly, and list item (4) permits aluminum or copper-clad aluminum without individual insulation where it is part of a cable assembly. There are multiple other methods permitted in the exception.
Doors and measurements in 210.8
New language in Section 210.8 explains how to determine the distance from receptacles. This is creating confusion in two scenarios. Where we have a laundry tub right next to a doorway and a receptacle is just on the other side, we are within 6 feet. The other problem we are having regards cabinet doors directly below a sink with a receptacle installed inside. Does this mean we do not need GFCI protection in these areas?
The text you refer to is a new second paragraph added to the parent text of 210.8 in the 2017 NEC revision cycle. This was added to provide the Code user with a prescriptive method to measure distance as 210.8(A)(7), (A)(9) and 210.8(B)(5) require. I agree with you that this text has created confusion. As written in the 2017 NEC, where the measurement to receptacle outlets would pierce a floor, wall, ceiling or fixed barrier, or would pass through a door, doorway, or window, the requirements of 210.8 do not apply.
The problem here is the reference to passing through a door or doorway. In my opinion, this warrants a tentative interim amendment. GFCI protection should be provided wherever this measurement passes through a door or doorway and a receptacle outlet is within 6 feet of a sink, bathtub or shower stall. The confusion will be corrected in the 2020 edition. See First Revision 7863, which deletes the words “door or doorway.”