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.

Office partitions

Can free-standing office furniture partitions be supplied with multiwire branch circuits? There are a dozen locations we need to supply with two circuits each, but the drawing states "no multiwire branch circuits."

Multiwire branch circuits are not permitted to supply office furnishings. See Section 605.9(D), Multiwire Circuits, Not Permitted. This prohibits multiwire branch circuits in individual office furnishings or groups of interconnected office furnishings.

210.8(B) GFCI circuit breakers

The expansion of GFCI protection to include single-phase receptacles up to 50A and three-phase receptacles up to 100A has created significant problems in finding breakers to comply. We do a lot of work in existing kitchens and eateries and cannot get bolt-on Type 2 and three-pole GFCI circuit breakers. What can we do?

The requirements of 210.8(B) are limited to receptacles supplied by single-phase branch circuits rated 150V to ground or less, 50A or less and three-phase branch circuits rated 150V to ground or less, 100A or less. An internet search for the existing panelboards and bolt-on type circuit breakers you mentioned reveals that GFCI devices for those panelboards are not commercially available. However, there are multiple products that are readily available to provide the required GFCI protection. These devices can be installed at the panelboard or at the point of utilization, or anywhere in between (must be readily accessible) in a manner similar to external devices used for surge protection. These devices have test and reset capabilities similar to standard Class A GFCI receptacles and circuit breakers. In the future, device manufacturers may develop GFCI-type receptacles to fill the void.

Replacing circuit breakers

An apartment complex we do work for was informed by their insurance carrier that they should completely replace all the load centers installed in the 1970s in each apartment. These panelboards contain stab-lock type devices that have a history of failure. We located a manufacturer of listed replacement circuit breakers for those panelboards, but the insurance company also wants new panelboards. Is this an NEC thing?

The NEC does not identify any brand or style of older circuit breakers as noncompliant. It is typical for insurance companies to push back on some types of older circuit breakers due to the devices’ history of failure. However, the NEC does not address this issue. The decision to replace all of the circuit breakers or panelboards in an apartment complex is a design issue left to the owner. In this case, the replacement of older electrical equipment is an issue between the owner and the insurance company. Perhaps you could present the replacement of all circuit breakers with devices that are listed for the existing panelboards as an option for the insurance company to consider.

Three-phase, 3-wire delta system

In a building with an existing two-phase, 5-wire system, we are installing a transformer with a 240V, three-phase, 3-wire, delta-connected secondary for a new machine. Can we install it ungrounded, or do we need to corner ground?

We must start in Section 250.20(B). Since the voltage to ground (if corner grounded) is 240V, we are not required to ground this separately derived system. See the definition of voltage to ground in Article 100. If you choose to move forward with an ungrounded secondary (permitted by 250.21(A)(4)), you must comply with 250.21(B) and install a ground fault detection system, and 250.21(C) for marking requirements. See 250.30(B) for grounding a separately derived (ungrounded) AC system.

If you choose to ground the system, 250.26(4) applies and one corner is grounded. See 250.30(A) for grounding a separately derived (grounded) AC system. Section 210.5(C) will also apply, and you must identify the labeling of ungrounded conductors. Section 200.6 will apply, and the grounded conductor must be identified as such. The rules for transformer secondary conductors in 240.21(C) apply, and the conductors must terminate in an OCPD.

Assuming that the OCPD will be a molded case circuit breaker, Section 240.85 applies. The circuit breaker protecting the transformer secondary conductors must have a straight voltage rating of 240V. Additionally, if this system is installed ungrounded, 240.85 does not permit a 2-pole circuit breaker to protect a three-phase corner-grounded delta circuit unless the circuit breaker is marked as 1Ø-3Ø (single-/three-phase) to indicate suitability. See 240.22(1), which would permit a straight rated 3-pole circuit breaker.

Panelboard height

In an existing dwelling unit, there are two panelboards stacked on top of each other, leaving the lowest circuit breaker handle at 12 inches above the finished floor. Is that compliant?

While the installation is not ideal from a maintenance or future work standpoint, it is not an NEC violation. This is no limit as to how low the center of the handle on a switch or circuit breaker can be; there is only a limitation on how high they can be installed. See sections 240.24(A) and 404.8(A) that require the center grip of the operating handle of a switch, a fused switch or a circuit breaker to be not more than 6 feet, 7 inches above the floor. There is no minimum height provided.

Aluminum terminations

Does the termination of aluminum conductors in SE/SER for a typical ATS/generator for optional standby require the application of an oxide inhibitor?

No. Where an oxide inhibitor is required, it will be noted in the manufacturer’s instructions and typically at the termination point. Listed terminations that require an oxide inhibitor today are driven by the product standards. In many cases, when required, the device will include the compound in the connector or device, such as wire nuts that are listed for splicing 12/10 AWG aluminum wire. This question is typically brought up by installers that regularly used an inhibitor in the 1970s and 1980s.

Aluminum wire manufacturers, the product standards and the NEC moved away from AA-1350 grade aluminum to AA-8000 series electrical grade aluminum alloys in 1987. See the definition of service entrance cable in Section 338.2. This requires that SE/SER be manufactured with a flame-retardant, moisture-resistant covering.

It is for this reason that SE/SER cable is always constructed with thermoset insulation marked XHHW and XHHW-2. See Table 310.104 that notes the properties of XHHW and XHHW-2 to be flame retardant and moisture-resistant, and Section 310.106(B), Conductor Material, requires Type SE/SER cables to be constructed using AA-8000 series electrical-grade aluminum. Through research, testing and decades of use, AA-8000 series electrical-grade aluminum is recognized as extremely reliable, with creep rates the same as copper. It is also important to understand that many listed lugs or termination points for copper and aluminum are made of aluminum.

GFCI for EV chargers

Do electric vehicle chargers installed in or on a dwelling unit need to be GFCI-protected? We have been told to do so, but cannot locate a requirement. Would that GFCI protection also protect receptacles on the vehicle for off-board use?

Section 625.54 requires all receptacles installed for the connection of EV chargers be GFCI-protected. As this requirement is limited to receptacles, a hard-wired EV charger would not require the branch circuit to be GFCI-protected. See Section 625.60 that addresses receptacles installed in the EV for supplying use equipment from the EV. This section drives the EV product standards and requires overcurrent and GFCI protection for all receptacles on the EV. There are various ways for the manufacturers to provide GFCI protection. Section 625.22 requires the EV equipment to be provided with a listed system of protection against electric shock of personnel.

Header image by Shutterstock / Zern Liew.