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.

Panelboard location in closet

Understanding that overcurrent protective devices (OCPDs) cannot be installed in clothes closets, we have a tough situation. In a new 100-unit condominium, each unit has a walk-in closet that has a common area with shelves and then opens into separate spaces for hanging clothes. There is a 30-inch-wide space between two doorways (to access closet rod spaces) where we want to locate a panelboard. The area in front of it has more than the needed workspace and is a walkway to enter the back spaces. Would a panelboard be prohibited?

Section 240.24(D) prohibits OCPDs in the vicinity of easily ignitable material. The reference to clothes closets is prefaced with “such as,” meaning that other spaces may also contain easily ignitable material. Each installation must be considered individually. OCPDs (for example, circuit breakers in a panelboard) are prohibited in a typical clothes closet because clothes will hang in front of the enclosure. The key to properly applying this requirement is determining the vicinity, meaning the area around the OCPDs. As described, the panelboard installation would not be in the vicinity of OCPDs and would be permitted.

Retention ponds and fountains

Engineer notes on approved electrical drawings state “install equipotential bonding where required.” Where? The installation consists of a new service and two circuit breaker enclosures for floating fountains in two large retention ponds that contain water year-round. What is required?

A retention pond is an artificially made body of water, and NEC Article 682 applies. See Section 682.33(A), which requires an equipotential plane to be installed adjacent to all outdoor service equipment or disconnecting means that have a metallic enclosure, control equipment in or on water and are likely to become energized. The equipotential plane must be installed in the area below and around the equipment a minimum of 36 inches in all directions from which a person would be able to stand and come into contact with the equipment.

The equipment supplied (in this case, fountains) does not require an equipotential plane. Bonding conductors are required to be solid copper, insulated, covered or bare, and not smaller than 8 AWG. Splices/connections must be by exothermic welding or by listed pressure connectors or clamps labeled as being suitable for the purpose and made of stainless steel, brass, copper or copper alloy. 

The equipotential plane must be bonded to metallic outdoor service equipment, disconnecting means, controls and the walking surfaces directly below the equipment at a distance of 36 inches as stated above. The equipotential plane must be bonded and consist of wire mesh or other conductive elements on, embedded in or placed under the walking surface within 3 inches.

Ventilating openings

Can you settle a disagreement we are having? Is it permissible to take flexible conduits directly into a transformer enclosure by punching holes in the ventilated wall or bottom of a transformer enclosure?

No. See Section 450.9, which prohibits ventilating openings of transformer enclosures from being blocked by walls or other obstructions, including a raceway entry. Where there are obstructions blocking ventilating openings, temperatures can reach values higher than the transformer rating. This requirement also mandates that the top surface of transformer enclosures be marked to prohibit storage that would increase the temperature. Section 450.10(A) requires a terminal bar for all grounding and bonding conductor connections (where separate equipment grounding conductors and supply­-side bonding jumpers are installed). This terminal bar is not permitted to be on or over any vented portion of the enclosure. It is also important to note that grounding electrode conductors are not permitted to be installed through a ventilation opening of a transformer enclosure. See 250.64(G).

Raceway or support system?

Can we use cable tray for feeder conductors supplying panelboards in a shopping mall? Each feeder would be (4) 1/0 copper THWN separated in the tray. The tray would be run above a service corridor behind all the stores. It was flagged in plan review; we are not sure why.

It is important to understand that cable tray is not a raceway. See Section 392.10, which clarifies it is a support system. The installation you described is not NEC compliant. See Section 392.10(B), which limits the use of single insulated conductors to industrial establishments. There are other options. For example, panelboards in each store can be supplied with Type MC cable installed in cable tray.

GFCI requirements

While studying to take my contractor’s exam, a practice question took me to 445.20(A), which requires GFCI protection for a generator with a floating neutral. Why? It just doesn’t make sense to me; we use them when camping without issue.

Requirements for GFCI protection for receptacles on 15-kW and smaller generators saw a significant amount of discussion and review over multiple NEC revision cycles. One must consider how these generators are typically used. Many homeowners purchase generators for use only during power outages. The use of an unbonded floating neutral is typical. The use of an unbonded, floating neutral generator in a recreational manner, such as camping, is unlikely to create a scenario where a shock incident (current flow through the body) could occur. A double fault scenario would be required. The first fault would ground the generator and the second create a path through the body. 

However, the technical committee must review all uses of portable generators when considering safety-driven requirements. These generators also are used with manual transfer switches to supply limited power to dwellings during storm-related events or power outages. GFCI protection for people is necessary. When the generator is connected to a manual transfer switch, the neutral is no longer floating; it is solidly grounded through the service-supplied neutral conductor.

517.13 wiring methods

Are we required to install healthcare facility wiring methods (517.13) in drug store areas used for flu shots, etc.?

No. See the first section in Part II: “Wiring and Protection.” Section 517.10(A) explains that in general, all patient care spaces must comply with Part II, which includes 517.13. Spaces not covered by Part II are addressed in 517.13(B). See list item 517.13(B)(1) that exempts areas used exclusively for intramuscular injections.

Oversized EGCs

Are we required to upsize the equipment grounding conductor (EGC) when oversizing conductors due to more than three current-carrying conductors in a raceway? We have a recurring situation with existing raceways forcing us to use ampacities at 50%.

No. See 250.122(B), which contains requirements for increasing the EGC size. Where current-carrying conductors are increased in size for situations such as long distances (voltage drop), the size of the EGC must be increased proportionately to the increase in circular mil area of the ungrounded conductors. However, this requirement specifically exempts installations where conductors are increased in size due to ambient temperatures [310.15(B)] and more than three current-­carrying conductors [310.15(C)].

Arc energy reduction for fuses

If we use 1,100A fuses in a fused disconnect, is arc energy reduction required? We failed an inspection with 1,200A fuses. We cannot get a fused disconnect with an energy-reduction maintenance switch in a reasonable amount of time due to supply chain issues.

Yes; the use of 1,100A fuses would not require a means of arc energy reduction. This requirement is based solely on the size of the fuses installed. It is important to note that Section 240.67(B) contains a performance-based requirement mandating a means of arc energy reduction only where the fuse does not clear in 0.07 seconds or less at the available arcing current. The engineer of record can make that determination. If the performance requirement is met, 1,200A fuses would be permitted.

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