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.

Agricultural building wiring

We are wiring a new structure on a large farm that will be used to store and maintain tractors and other equipment. There will also be locker rooms and showers for employees. Does Article 547 apply in this new building?

No. Article 547 will not apply to that building/structure. See 547.3, which clarifies that buildings and structures that do not have conditions as specified in 547.1 must have electrical installations in accordance with all applicable articles in the NEC. Article 547’s scope is explained in Section 547.1. Two types of buildings/structures are considered to be agricultural buildings. Section 547.1(A) addresses buildings with excessive dust and dust with water, and 547.1(B) addresses buildings where a corrosive atmosphere exists. The new structure mentioned in your question does not fall under the scope of Article 547 and must meet all other applicable NEC requirements.

Accessible versus readily accessible

After a failed electrical inspection, we have been going in circles about definitions of “accessible.” It is confusing. If you need more than one definition for the same word, I think the requirement needs modification! In a commercial kitchen, we installed GFCIs behind refrigeration units that can be pulled out into the aisle to access the receptacle. It failed inspection and we had to get GFCI circuit breakers.

Section 210.8 contains requirements for GFCI protection of personnel. The parent text of this section requires that the GFCI be installed in a readily accessible location. If access to a GFCI device requires removing obstacles, such as a refrigeration unit, the GFCI device is not readily accessible.

There are three definitions in Article 100 for accessibility. The first definition is “accessible (as applied to equipment),” which is very basic and states that close approach is possible and there are no locked doors or elevation issues. The second definition is “accessible as (applied to wiring methods),” which means that we do not have to damage the building structure or finish to remove or expose the wiring methods. The third definition applies to your question, “readily accessible,” which means that access is not impeded in any manner: no obstacles, no ladders and no need to climb or crawl. These definitions provide significant clarity and usability. As always, if you think that a definition or requirement can be improved, the NEC technical committees welcome your public input.

Use of unlisted appliances

During a plan review, I saw that the engineer identified multiple refrigerated cases used for takeout that were not listed, but his note stated they met all applicable requirements. It turns out that the owner purchased the refrigerators some time ago. How would we know that this equipment meets U.S. standards?

The owner and engineer have only two options. The first is to have a field evaluation performed on the existing refrigeration equipment or they can buy listed appliances. See Section 422.6 that requires all appliances operating at 50V or more to be listed. The refrigerated cases for takeout in question are appliances as defined in Article 100. An appliance is utilization equipment, other than industrial, built in standardized sizes or types to perform a function such as refrigeration.

Bonding of piping systems

When completely rewiring a home, is it required to bond existing copper piping that is used as a soil line? The dwelling unit was built in the late 1960s, and using 3- and 4-inch copper for soil lines was popular then for the inside of the home. The inspector wanted it bonded. Was that required?

Not likely. Bonding of piping systems is covered in Section 250.104. All metal underground water piping (where present) is required to be part of the grounding electrode system (GES). Section 250.50 requires that a metal underground water pipe [see 250.52(A)(1)] be bonded to the GES. Metal water piping that does not qualify as a grounding electrode is required to be bonded. See 250.104(A). The metal piping in question is not metal water piping; it is a soil line that likely connects to cast iron or PVC piping to public sewer lines. Other metal piping is addressed in 250.104(B). This requirement applies to all metal piping other than metal water piping.

Where these other piping systems, including gas piping, are “likely to become energized,” they must be bonded in accordance with one of the methods provided in 250.104(B). The key phrase in this requirement is “likely to become energized.” For example, where a piping system supplies utilization equipment that is supplied with a branch circuit, the equipment is considered “likely to become energized,” and the branch circuit supplying the equipment is the source that is considered likely to energize the piping system. Section 250.104(B) list item (1) recognizes that the required bonding is achieved with the equipment grounding conductor run with the branch circuit to supply the utilization equipment. The metal piping in your question is copper used as a soil line, which would not likely be connected to utilization equipment because it only serves to handle the discharge from sinks, tubs, showers and toilets. Copper soil line piping is not “likely to become energized” and does not require bonding.

Capacitors for motors

When a capacitor is installed immediately adjacent to a motor, are we permitted to reduce the size of the motor circuit conductors because of the improved power factor?

No. Where a motor installation includes a capacitor that is connected on the load side of the motor overload devices, the NEC requires the motor overload devices be based on the improved power factor of the motor circuit. Section 460.9 prohibits the improved power factor from being applied to the motor circuit conductors that must be sized in accordance with 430.6 and 430.22.

Type NM in concrete

Is type NM cable permitted to be installed in concrete when used for temporary lighting? We were forced to run new temporary lighting circuits when a risk-management company did an audit and had issues with Type NM cable in concrete. We have been doing it this way for years without any issues. Isn’t this permitted in the NEC?

No. See Section 90.3, which explains that the NEC is made up of Article 90 and nine chapters. Chapters 1–4 apply generally. This means all requirements in chapters 1–4 apply in every electrical installation. Chapters 5, 6 and 7 are special and may supplement or modify the requirements in chapters 1–7. Article 590 does not modify the general requirements in Chapter 3 to allow Type NM cable in concrete. Additionally, Section 590.2(A) clarifies that all other requirements in the NEC apply except where they are specifically modified in Article 590. See Section 334.12(A)(9), which prohibits Type NM cable from being installed in cement, concrete or aggregate.

SE, SEU and SER

In the NEC, cable types SE and SER are used, but not SEU. What is SEU? Can it be used underground? Is it equivalent to type USE?

The confusion is based on how some cable manufacturers identify their products. The acronym SEU simply means a service cable that is unarmored. The NEC is clear; see the title of Article 338, only types SE and USE are listed. Types SEU and SER are type SE cable, and the requirements are the same. Type USE cable is very different; it is permitted to be installed underground, but not as interior wiring.

Header image by Shutterstock / Refrigerated Case.