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.

Luminaires mounted on trees

We have approved drawings with outdoor lighting fixtures mounted on trees—is that NEC compliant?

Yes, see 410.36(G), which permits outdoor luminaires and associated equipment to be supported by trees. It is important to note that there are two informational notes following this permissive requirement that send the Code user to sections 225.26 and 300.5(D). While a luminaire is permitted to be supported by a tree, Section 225.26 prohibits vegetation such as trees from being used as a support for overhead conductor spans. Section 300.5(D) requires underground conductors and cables to be protected from damage.

Island receptacle requirements

Everyone is talking about the changes for receptacles in kitchen island countertops. It is hard to believe that we saw an increase of required receptacle outlets in 2020 and then none in 2023. We are modifying the township’s guidance for homeowners when applying for permits. Essentially, the 2023 NEC takes us back to 2017 requirements if one installs a receptacle outlet, right?

No, there are significant differences. The requirement in 210.52(C)(2) simply states that if you do install a receptacle outlet (it is not required) for an island or peninsular countertop, it must be in accordance with 210.52(C)(3). This requires that the receptacle outlet be installed (1) on or above the countertop, but not more than 20 inches above. There is typically no way to install an outlet above an island countertop, so this only permits installation “on the countertop,” and (2) “in a countertop” using receptacle outlet assemblies listed for use in countertops. 

The major difference here is that in the 2017 NEC, provisions existed to install the receptacle outlet in the side of a cabinet below the countertop. However, the 2023 NEC mandates a receptacle outlet installed in an island kitchen countertop be installed “in or on the countertop.”

1,200A, 480/277V temporary service

For a 480/277V, 1,200A temporary service, we are installing used equipment with a 1,200A fused (fused at 1,200A) disconnect as the service disconnect. A 1,200A feeder then supplies a used switchboard. Is this equipment considered reconditioned? Do we need arc energy reduction? I don’t see any mention of it in Article 590.

Based on the information in your question, the fused disconnect and switchboard are used but in good operating condition and would not be considered reconditioned. The equipment is used. See the definition of “reconditioned” in Article 100. To be considered as “reconditioned,” the equipment must have had issues of some type and was “restored to operating conditions.” The process of reconditioning is different from normal servicing of equipment that remains within a facility or replacement of listed equipment on a one-to-one basis.

The requirements for arc energy reduction in 240.67 apply because fuses rated 1,200A or higher are installed. It is important to note that chapters 1–4 apply to all temporary power installations. See 240.67(B), which provides a performance-based requirement that fuses have a clearing time of 0.07 seconds or less at the available arcing current, or a means of arc energy reduction must be provided and must be set to operate at less than the available arcing current.

There are additional requirements not mentioned in your question. The requirement for arc energy reduction is one of many that apply. See Section 230.95, which requires ground fault protection of equipment for all solidly grounded wye electric services of more than 150V to ground but not exceeding 1,000V phase-to-phase for each service disconnect rated 1,000A or more. The same requirement applies for feeders; see Section 215.10. Where used overcurrent devices are used for temporary power, Section 590.8(A) requires they be examined to ensure they were properly installed and maintained, and there is no evidence of impending failure. The fuses (or circuit breakers) for 480/277V (solidly grounded wye) temporary services must be current limiting. See Section 590.8(B).

Mixing branch circuits

Understanding that we cannot mix emergency system circuits with other wiring, is it permissible to mix branch circuits supplied by an optional standby system with normal circuits in raceways and junction boxes, etc.?

Yes, it is permitted. See Section 702.10, which prescriptively permits optional standby system wiring to occupy the same raceways, cables, boxes and cabinets with other general wiring.

Older motion sensor switches

During a tenant space renovation, maintenance personnel informed us that the older existing switches that had marked on, off and auto positions allowed current to flow in the off position. Have you ever heard of this? Is that permitted in the NEC or product standards?

Those devices are at least 25 years old. The older design allowed a trickle flow of current through an impedance to create a small voltage, keeping the motion sensor active. There were documented issues of shock incidents where those devices were in the off position. This was addressed by a requirement in Part II, Construction Specifications, of Article 404. See 404.20(B), which mandates that where a device is moved into a marked off position, the switch must completely disconnect all ungrounded conductors to the load it controls. This NEC requirement drives the product standards prohibiting the older design.

Mounting fire pump controllers

To support a (larger) replacement fire pump controller in a fire pump room, we installed floor-to-ceiling treated 4x4s and plywood backing. The inspector failed the job and stated that wood was not permitted. Where is he getting his information?

The inspector is correct. Section 695.12(F) requires that all fire pump control equipment be mounted in a substantial manner on “noncombustible” supporting structures.

Does 240.4(B) apply?

As a designing engineer, I have always specified 500 kcmil copper for transformer secondary conductors on a 150 kVA transformer secondary at 208/120V because the maximum output is 416A and connected loads are typically in the ballpark of 320A. A new inspector is requiring 600 kcmil copper. This means rework and significant additional cost. This is overkill and it is ridiculous!

Thanks for your question, and I certainly hope that you engage in the consensus process by submitting a public input to the technical committee with purview over Article 240. The inspector is correct. No one (the inspector included) wants to see rework. 

The requirements for transformer secondary conductors apply; see the parent text in Section 240.21(C). The second-to-last sentence clearly states that the provisions of 240.4(B) are not permitted for transformer secondary conductors. The rated ampacity of a 500 kcmil copper in the 75ºC (167ºF) column is 380A. When used as a transformer secondary conductor, 500 kcmil copper is limited to termination in a 350A overcurrent protective device. The same limitations apply to feeder taps in 240.21(B).

Interrupting ratings

Where the utility delivers high values of available fault current, can we install an overcurrent device as the service disconnect with an interrupting rating (IR) of 65k and then supply panelboards rated at 22k IR? We cannot find anything that prohibits such an installation.

There are two methods for compliant series combination systems. The most common is a tested series combination system as permitted in 110.22(C). This is commonly seen in mass-produced panelboards supplied with a main overcurrent protective device rated at 22k IR supplying downstream circuit breakers rated at 10k IR. The manufacturer tests the series combination system and marks the series combination ratings on the equipment. The scenario in your question is very likely not a tested series combination. See Section 110.22(B) that allows an engineered series combination system in accordance with Section 240.86(A). That will require a licensed professional engineer engaged primarily in the design or maintenance of electrical installations to select, document and stamp the designed installation. 

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