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 2023 NEC.

Intrinsic safety

While supplying line-voltage circuits to new industrial control panels on a production line for a pharmaceutical firm, the engineer referenced separation from intrinsically safe circuits. What makes them safe?

As defined in Article 100, intrinsically safe involves a type of protection where any spark or thermal effect is incapable of causing ignition of a mixture of flammable or combustible material in air under prescribed test conditions. Intrinsic safety is one of many protection techniques listed in Section 500.7 and is permitted for equipment in Class I, Division 1 or 2; Class II, Division 1 or 2; or Class III, Division 1 or 2 locations.

Permitted wiring method

Can we use Type NM cable in a pole barn used in a commercial setting? This building is designed to store commercial vehicles and perform minor work/maintenance on the vehicles. The building type is 5B. We are confused by a note on the drawings that states it is “Moderate Hazard Storage S-1.” Does that matter?

Based on the limited information provided, Article 511 will apply to this installation, as it is a commercial structure used as a repair garage and vehicle storage. With respect to the use of Type NM cable, look at the uses permitted in Section 334.10. See 334.10 list item (3), which allows type NM cable in other structures including type 5 construction.

However, this permission requires the Type NM cable to be concealed within walls, floors or ceilings with a 15-minute finish rating. This means that Type NM may not be feasible and a different wiring method would be required. As stated in your question, only minor repair work will be performed. With the limited information provided, you must refer to Article 511 for additional requirements. For example, see Table 511.3(C) to determine if there are or will be classified locations. See also 511.12, which requires all 125V, 15/20A receptacles in the repair areas to be GFCI protected. It is likely that any receptacles in the structure could be used in that manner, so all must be GFCI-protected. 

The reference on the drawing to the structure being classified as “Moderate Hazard Storage S-1” is a building code issue and requires that the building code official apply requirements in the International Building Code Section 406.8, as applicable.

Countertop vs. work surface

What’s the difference between countertops and work surfaces, addressed in 210.52(C)?

Both of these terms are defined in Article 100. A countertop is a fixed or stationary surface typically intended for food preparation and serving, personal lavation (the act or an instance of washing or cleansing) or laundering, or a similar surface that presents a routine risk of spillage of larger quantities of liquids on outlets mounted directly on or in the surface. Countertops are typically located in kitchens, bathrooms and laundry rooms. A work surface may be similar in construction, and may look exactly the same as a countertop, but it is located in an area where the intended use is for dry tasks other than those identified for countertops and has an incidental risk of spillage.

AFCI requirements

In an apartment house project, the electrical inspector told us to protect all the house panel branch circuits for lighting, receptacles, etc., in common areas with AFCI devices. An AFCI is required because they are in the same wall in some areas. These circuits do not originate in nor do they supply a dwelling unit. Is AFCI protection required? How about AFCI and common areas in other occupancies?

No. Section 210.12 contains requirements for AFCI protection, and the spaces identified in your question are not addressed. The parent text of 210.12 clearly states that AFCI protection applies in the spaces or scenarios identified in 210.12(B) through (E). It further states that any of the means of protection identified in 210.12(A), list items (1) through (6), may be used. Your question is about an apartment complex, which is by definition a multifamily dwelling—a building that contains three or more dwelling units.

A dwelling unit is a single unit, providing complete and independent living facilities for one or more people, including permanent provisions for living, sleeping, cooking and sanitation. The common areas in an apartment complex are not part of a dwelling unit and 210.12(B) does not apply. The inspector may be correct in that those branch circuits may be located in a wall that is common to a dwelling unit. However, that does not mandate AFCI protection.

If we were to buy into that concept, all 120V, single-phase, 10A, 15A and 20A branch circuits supplying outlets or devices in any dwelling units would require AFCI protection. There would be no need for 14 list items identifying areas in the dwelling unit requiring AFCI protection. In other than dwelling units, the requirements in 210.12(C) and (D) provide clarity, and AFCI protection would not be required in common areas. It would only be required in the six locations listed for dormitory units; guest rooms and guest suites of hotels and motels; areas used exclusively as patient sleeping rooms in nursing homes and limited-care facilities; and areas designed for use exclusively as sleeping quarters in fire, police, ambulance, rescue and ranger stations and similar locations. 

Supply chain problems

We have an installation that is 90% complete, but the metering center was back-ordered for the second time in over a year. The owner wants to begin renting these spaces as soon as possible. There are 12 units, each of which has a 100A panelboard with a 100A main circuit breaker. We were able to get 12 meter/circuit breaker combination enclosures with 200A circuit breakers. Can we supply the feeders (sized at 100A) already installed and enclosed at 200A? It is a safe installation, because the 200A circuit breaker will protect the feeders from short circuits and the 100A circuit breaker will protect the feeder from overloads.

No, your proposed solution is noncompliant. The NEC requires all conductors be protected at their rated ampacity at the point of supply, which they would not be in your proposed solution. See the parent text in Section 240.21. This means they would be by definition “tap conductors” and would be subject to the requirements in 240.21(B).

Transformer disconnecting means

An apprentice informed us that transformers now require a disconnecting means and labeling. Can it be the circuit breaker protecting the primary? Where do we have to label the location of the disconnect?

Section 450.14 requires a disconnecting means located either in sight of the transformer or in a remote location. Where the disconnecting means (typically the overcurrent device protecting the transformer primary) is not within sight of the transformer, the disconnecting means must be lockable in the open position in accordance with Section 110.25, which mandates that the means for applying a lock must remain in place with or without the lock installed. Where the disconnect is not within sight, its location must be field marked on the transformer. 

Listed products

Is there more than one company that lists products where listing is required by the NEC? If so, where is that list?

Yes, there are many nationally recognized testing laboratories. Section 110.3(C) mandates that listing or “product certification” be performed only by recognized, qualified electrical testing laboratories. The listing must be in accordance with the applicable product standards. There is an informational note that follows this requirement to inform the Code user that OSHA recognizes qualified electrical testing laboratories. That list is readily available online.

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