Jim Dollard has an extensive background in codes and standards. Send questions about the National Electrical Code (NEC) to Jim at [email protected]. Answers are based on the 2020 NEC.

Is an Airbnb space a guest room?

The renovation of a two-story commercial building includes retail spaces on the first floor and what seems to be rooms for rent on the second floor. These dwelling units have bedrooms, full bathrooms, a living space and more. When we questioned the need for AFCIs in these rooms, we were told by the general contractor that they were Airbnb rooms and not a hotel or motel, and AFCIs are not needed. Is that right?

No, those rooms are considered guest rooms or guest suites with respect to the application of the NEC . See the definitions of guest room and guest suite in Article 100. Typically, renting these spaces requires the owner to qualify the space as a hotel or motel with respect to licensing, property management, taxes, etc. Section 210.12(C) requires AFCI protection for all 120V, single-phase, 15A and 20A branch circuits supplying outlets in guest rooms and guest suites. It is important to note that if any of those guest rooms or guest suites include permanent provisions for cooking, Section 210.17 requires those rooms to have branch circuits installed to meet the requirements for dwelling units.

Underground pool lighting

During a recent trench inspection for a pool job, the inspector said the conduit for low-voltage lighting did not need to be at 18 inches and that a reduced depth was permitted. Is that correct?

In the 2014 NEC , requirements for underground pool wiring were located in Section 680.10 and Table 680.10. These requirements for underground wiring were modified during the 2017 NEC revision cycle to more adequately address the underground wiring installations for pools, etc., that operate at not more than the low-voltage contact limit. The net result is that the previous table for underground wiring (Table 680.10) was deleted, and the requirements of Table 300.5 are now referenced in Section 680.11 (2017 and 2020 NEC ).

The locations in the first column of Table 300.5 do not specifically address pool installations. Therefore, the column marked “All locations not specified below” applies. See Column 5, which addresses “Circuits for Control of Irrigation and Landscape Lighting Limited to Not More Than 30 Volts and Installed with Type UF or in Other Identified Cable or Raceway.” See the burial depth listed for this location, which is 6 inches and has two superscript identifiers (6a,b) sending the user to the associated table notes. Remember that table notes are enforceable, and they are not informational. The table note for superscript b permits a depth of 6 inches for pool, spa and fountain lighting, installed in a nonmetallic raceway and limited to not more than 30V where part of a listed low-voltage lighting system.

Elevator disconnect in a pit

We have an elevator where the controller is in the pit. We’ve done these before, and we usually install the disconnect right at that elevator doorway, just above it. We were going to do that here. The engineer feels that we should install a disconnect for that controller in the pit. The elevator people don’t want it. Does the controller need a disconnect in the pit?

Part VIII of Article 620 addresses machine rooms, control rooms, machinery spaces and control spaces. See Section 620.71. This requires guarding the controller. Section 620.71(A) permits the controller to be located outside an elevator equipment room. Where this is done (as in this installation), the disconnecting means must be located adjacent to the controller or must be an integral part of the controller. The answer is yes, a disconnect at the controller is required.

Ground rods’ effectiveness

As an inspector, I try to ensure the safest installation possible through NEC requirements. On a job at a dwelling unit, they hit solid rock just below the soil, causing a redesign of the home. Ground rod installation was not possible, and they went 20 feet from the home to bury two rods at 30 inches. No metal water pipe exists. This is Code -compliant, but what good are the rods at that point? They do nothing.

I agree that, as installed, the two ground rods in this case will do little to increase the efficiency of the grounding electrode system. See Section 90.1 that explains that the NEC is not intended as a design specification and compliance with NEC rules provides for an installation that is essentially free from hazard, but not necessarily efficient.

The installer and the designer have many options with respect to grounding electrode installations. Ground rods with 6 AWG copper are permitted but may not be the most effective solution. Other options include installing concrete-encased electrodes, ground rings, plate electrodes and other listed electrodes. In all cases, more than one of these electrodes are permitted to increase the efficiency of the grounding electrode system.

Outside feeder

The installation of a 100A panelboard in a garage at a dwelling unit includes 80 feet of underground in 2-inch conduit and 35 feet or so across the existing garage ceiling. Does the Code require larger conductors for voltage drop? Can I use the same cable in conduit underground and across the attic of the garage exposed or should it all be in conduit? Is SER OK?

The conductors in question are outside feeder conductors. The NEC does not require oversizing conductors to compensate for voltage drop due to distance. See Informational Note No. 2 to Section 215.2(A)(1) for guidance on reasonable efficiency of operation. With the exception of fire pumps (695.7), voltage drop is typically a design decision that must be made by the designer or the installer unless the voltage falls below requirements for listed products [110.3(B)].

These conductors originate in a dwelling and are leaving that building to supply the garage. Section 225.32 applies and requires a disconnecting means either outside the garage or inside the nearest point of entrance for the conductors. That means you cannot run the 35 feet described in the garage without a disconnecting means in accordance with 225.32. The minimum size conductors would be 3 AWG cu or 1 AWG al.

Four conductors are required: two (2) ungrounded, one (1) grounded and one (1) equipment-grounding conductor (EGC). A grounding electrode system is required as per 250.32. See 250.32(A) and (B)(1). Two ground rods and a 6 AWG cu conductor that terminates in the disconnecting means and is bonded at that point to the EGC is permitted.

Type SER cable is not permitted to be installed underground in a permanent installation. SER is permitted to be installed underground in conduit only for temporary power and lighting as permitted in sections 590.4(B)(2) and 590.4(C)(2). The underground portion must be a raceway and use conductors rated for wet locations or a cable assembly, such as type UF. Type SER cable can be used for all of the aboveground portions of this installation. For example, in the garage, the load side of the required disconnecting means could be type SER.

Clothes closets

We have a question about installing a data/network panel inside a clothes closet. Obviously, overcurrent protection is not permitted. Would this product fall into a similar category? That would be an internal receptacle, router and modem, as well as RG6, Cat 6 and Cat 3 connecting blocks.

The location of overcurrent protective devices is addressed in Section 240.24. The prohibition in 240.24(D) applies only to overcurrent devices where easily ignitable material exists. This requirement provides an example that is a clothes closet. While a clothes closet may not be an ideal location for data panels, routers and modems, it is not a violation of the NEC .