Jim Dollard has an extensive background in codes and standards. Send questions about the National Electrical Code (NEC) to Jim at [email protected]. All answers are based on the 2023 NEC.

Measuring shore power to boats

How does the requirement for a boat leakage current measurement device impact the electrical contractor? Is this something we install, and if so, where is it installed? Do we need to check each boat?

The requirement for a leakage current measurement device applies only where more than three receptacles supply shore power to boats. They are required to be used to determine leakage current from each boat that will use shore power. The rule does not mandate that the electrical contractor perform these tests or that an inspector witness a test of each boat. See Section 555.35(D). These devices must be listed beginning on Jan. 1, 2026, and will be used by the marina owner or operator. An exception to 555.35(D) permits the shore power equipment to include a leakage indicator and alarm, and a separate device would not be necessary. Leakage current measurement is required to identify problem boats that contribute to current flow in the water and the possibility of electric shock drowning. An informational note suggests an annual test of each boat with the leakage current measurement device. This will allow the marina’s owner/operator to identify problem boats and instruct their owners to make necessary repairs before the boat is permitted to again use shore power. 

Service conductors through an eave

Can SE cable used for a service (existing) be run through an eave of a new porch or do we need to relocate those conductors?

The existing service conductors can remain and be run through an eave, provided they are installed in, or sleeved with, RMC or IMC. See Section 230.6(5). The best solution may be to reroute the conductors or install them in RMC with a service head to eliminate the chance of it allowing water through the eave.

Feeder for temporary power supply

When using premanufactured, listed boxes with 20A circuit breakers for temporary power, are they required to be supplied through a receptacle? Many of ours have the male cord cap removed and we hardwire them, most at 50A. The general contractor is telling us they must be supplied through a receptacle and an assured equipment grounding conductor program (AEGCP) must be in place. Is that right?

Premanufactured assemblies of that type may be supplied by a feeder that is hardwired or cord-and-plug connected. See Section 590.4(J), which prohibits branch circuits and feeders from laying on the floor or ground. This means that the assembly can be supplied with a hard-wired cord or cable assembly provided the conductors are not on the floor or ground at any point. 

We all know how difficult that is on an active construction site. Other trades will move the assembly and there is a significant likelihood the feeder ends up on the ground. That is an NEC violation and an OSHA citation waiting to happen. The feeder could be installed as an “extension cord” with the premanufactured cord and male cord cap provided with GFCI protection at the source or with an AEGCP in place. Section 590.4(J) requirements exclude extension cords.

Mixing service and feeder conductors

Are there any exceptions that would permit mixing service and feeder conductors? We are installing a service-rated transfer switch on a historic building, and there is literally zero space and all of the conductors must pass through the same wireway. Can we wrap the service conductors or something?

No, see Section 230.7, which prohibits the mixing of service and other conductors in the same raceway. Your question references wireway, which is a raceway. See the Article 100 definitions of raceway, metallic wireway and nonmetallic wireway. I suggest that you consult the local electrical inspector to determine a practical, feasible, Code-compliant solution. For example, it may be possible to oversize the wireway and, with the use of necessary fittings, run another raceway such as EMT through to enclose and isolate the feeder or service conductors.

Supervising a disconnecting means

Drawings state that the disconnect for a fire pump must be supervised. How do we get that done? There are three 400A (480/277V) service disconnects in separate enclosures for the building. There is another service disconnect located remote from those for the fire pump. The feeder conductors go underground to the fire pump controller.

As described in your question, the fire pump controller is supplied by a dedicated feeder as permitted in 695.3(A)(3). Section 690.4 contains requirements designed to maintain the continuity of the power source to the fire pump. There are two methods permitted. The first is direct connection of the power source to the fire pump controller, including direct connection to service conductors. In this case, supervision is not required. 

The second method is through a disconnecting means and overcurrent protective device. The disconnecting means must be supervised in accordance with 695.4(B)(3)(e). Three different methods are permitted, including central station, proprietary or remote station signal device(s), a local signaling service that causes the sounding of an audible signal at a constantly attended point and (perhaps the easiest method) locking the disconnecting means in the closed position. 

It is important to note that 695.4(B)(3)(c) requires the fire pump disconnecting means be marked as “fire pump disconnecting means.” The letters on this label must be at least 1 inch high and the label must be visible without opening enclosure doors or covers. Additionally, where an upstream fire pump disconnecting means is installed, a placard must be placed adjacent to the fire pump controller, informing maintenance personnel, etc., of the locations of the locked disconnecting means and the key.

Pool house receptacle requirements

Are tamper-resistant (TR) receptacles required in a shed/pool house in the yard of a single-family home?

Yes, see Section 406.12(1), which requires TR receptacles in dwelling units, including attached and detached garages and accessory buildings to dwelling units. While garages are specifically identified, accessory buildings include, but are not limited to, a shed, pool house, workshop, barn and more.

Structural steel as bonding jumper

I hope you can provide input on a debate we have in-house. One of the designing engineers requires full-size copper grounding electrode conductors (GECs) run from each grounding electrode to the service, while another uses building steel as a bonding jumper. Is that permitted?

Yes, see Section 250.68(C) for permissive GEC conductor connection requirements. The structural steel of a building can be used as a conductor to interconnect electrodes as part of the grounding electrode system. This means that multiple GECs can simply be bonded to the structural steel to complete the grounding electrode system.

Permitted to be ungrounded?

We are working on a battery system in an older facility that operates at 240V DC. The system is ungrounded. Does the NEC require this system to be grounded?

No, see Section 480.13, which permits battery circuits exceeding 100V between the conductors or to ground to operate with ungrounded conductors provided a ground-fault detector and indicator is installed to monitor the system for ground faults.

Header image source: stock.adobe.com / Scott Prokop