Jim Dollard has an extensive background in codes and standards. Send questions about the National Electrical Code (NEC) to Jim at firstname.lastname@example.org. Answers are based on the 2020 NEC.
In-law suite emergency disconnect
We installed an emergency disconnect for a new dwelling unit in a combination meter housing and disconnect as permitted in 230.85. This project included a second, smaller dwelling unit as an in-law suite that we supplied with a 200A feeder underground. Since the in-law suite is a dwelling unit, was an emergency disconnect required? We did not install one and the inspector approved the job.
The installation you described complies with the requirements for an emergency disconnect in 230.85 of the 2020 NEC . This section requires that a disconnecting means having a short-circuit current rating equal to or greater than the available fault current must be installed in a readily accessible outdoor location for all service conductors supplying one- and two-family dwelling units. This requirement applies only to service conductors. The supply to the second dwelling unit is an outside feeder and must be installed in accordance with Article 225.
It is interesting to note that this issue is being addressed in the 2023 NEC cycle, and it is likely that, moving forward, the feeder-supplied dwelling unit will require an emergency disconnecting means.
Cord-and-plug connected range
Is it permissible to install an electric range in a dwelling with a cord and plug where the range must be pulled out to disconnect?
Yes, provided that you install a disconnecting means in accordance with 422.31. In this case, that would require a circuit breaker within sight of the range, or it must be capable of being locked in the open position in compliance with 110.25. See also 422.33(B), which permits cord-and-plug-connected electric ranges where the attachment plug and receptacle connection is at the rear base of the range and is accessible from the front by the removal of a drawer.
We are completely renovating an apartment complex one floor at a time. Each floor has a common area laundry with six washers and six dryers. Is AFCI protection required for the common laundry areas on each floor?
No, as described in your question, the laundry area is not part of a dwelling unit. Each apartment will be considered as a dwelling unit. In this case, the washers and dryers are accessible to, but not part of, a dwelling unit. The parent text of Section 210.12, “Arc-Fault Circuit-Interrupter Protection,” requires compliance with 210.12(A), (B), (C) and (D). The first three subdivisions tell us where AFCI protection is required: (A) dwelling units, (B) dormitory units and (C) guest rooms and suites and patient sleeping rooms in nursing homes and limited-care facilities.
Section 210.12(D) applies only to branch-circuit extensions and modifications. The requirements of 210.12(A) apply only to the specific areas identified (laundry areas included) in dwelling units. The laundry area as you described it is not inside or part of a dwelling unit. This same concept holds true for the other venues addressed in this section. For example, a careful look at 210.12(B) reveals that the title very specifically restricts this requirement to dormitory units and not dormitories. There are dormitory units that contain a laundry area within the unit and any 120V, single-phase, 15- and 20-ampere (A) branch circuits supplying outlets and devices in the laundry area would require AFCI protection. However, as written, it is clear that a common laundry area that may be in the basement of a dormitory would not require AFCI protection.
120- and 277-volt circuits
I know that we can install a 277V circuit in the same conduit with 120V circuits. We installed circuits in this manner to a security shack on the loading dock. I was questioned as to where in the NEC this permission exists. I cannot find it, can you help?
This is a general question about the installation of conductors and is addressed in Section 300.3. Where conductors of different systems are installed, 300.3(C) applies and 300.3(C)(1) permits conductors installed in circuits rated 1,000V nominal or less to be installed in the same equipment enclosure, cable or raceway. Where this is done, this requirement mandates all the conductors that are mixed in the same enclosure, cable or raceway have an insulation rating equal to the maximum circuit voltage applied to any conductor in the group.
It is important to note that this installation contains branch circuits from more than one nominal voltage system, and the requirements of 210.5(C)(1) apply. This requires each ungrounded conductor of all branch circuits in that occupancy be identified by phase or line and by system voltage class at all termination, connection and splice points. This is a common installation requirement and mandates, in general, permanent posting of the identification at each branch-circuit panelboard or similar branch-circuit distribution equipment.
Documenting in a readily available manner is also permitted. In the installation you described, you have installed grounded conductors from different systems in the same raceway and 200.6(D) for identification of grounded conductors requires that they be identified by system. Additionally, now that you have mixed grounded conductors of different systems in the same raceway, the permanent posting required for ungrounded conductors in 210.5(C)(1) must be supplemented with how you are identifying the grounded conductors of different systems.
Parallel feeder taps compliant?
In a small industrial installation, an engineer has provided us with drawings to add an 800A feeder at 208/120A that will run the length of the building. The drawings show two 4-inch conduits, each containing four 500-kcmil copper conductors running through two junction boxes (JB) and terminating in a third JB. At each JB location, we will tap into the 800A feeder to supply a 400A panelboard. The issue is that the drawing shows us tapping into one set of parallel conductors for one of the panelboards and tapping two panelboards from the other set of conductors. The engineer told us that the load calculations permit this installation. Is this permitted, with nothing in Article 310 prohibiting it?
No, the installation you described contains multiple NEC violations. The 800A feeder is permitted in parallel using 500-kcmil copper conductors. We will assume the insulation is THWN. The rated 75°C ampacity for each conductor is 380A. 380 + 380 = 760A. Section 240.4(B) permits us, in this case, to round up to 800A. Each tap made into the parallel feeder must connect to all conductors of the paralleled set. This requirement is not found in the general rules for paralleled conductors in 310.10(G); it is located in 300.3(B)(1) that provides general requirements for the installation of all conductors. This means that each of the 400A panelboards must be supplied from both sets of conductors in the parallel feeder. The supply to each panelboard will be a feeder tap that is in parallel.
Section 310.10 applies and requires a minimum of 1/0 copper for conductors in parallel. While that will not impact this installation, tapping into a smaller overcurrent protection device from this feeder, such as a 200A panelboard, would require parallel 1/0 AWG copper conductors. In this installation, each 400A panelboard must be supplied copper conductors, with a minimum size of 3/0 AWG, from each parallel set. It is also important to note that feeder tap conductors are not permitted to be rounded up to the next-higher standard overcurrent device rating as is permitted in 240.4(B). See the parent text in 240.21(B).