Code Change Summary: New language was added for existing branch circuits serving specific appliances where the service equipment is now feeder supplied.

Some electrical services are configured with a simple meter socket enclosure supplying an interior electrical service panel that is separate from the meter socket enclosure. A short run of service conductors or service entrance cable from the meter box to the separate service panel supplies the premises electrical system.

Often, an existing meter socket enclosure without a service disconnect nears the end of its life and needs replacing. Sometimes the meter socket is upgraded and replaced with a meter socket/combo unit equipped with a main service disconnect which can also satisfy the new requirement in Section 230.85(C) to have a readily accessible exterior emergency disconnect. When this occurs, and the equipment is identified as permitted in Section 230.85(E)(1)(1), the existing service conductors running from the meter socket enclosure to the existing service panel now become a feeder.

Sometimes a homeowner adds a standby generator to the existing premises electrical system. Typically, the existing service conductors or service entrance cable between the meter box and the existing service panel is interrupted to install a transfer switch that is suitable for use as service equipment (SUSE rated) and has a main breaker that will serve as the new service disconnecting means.

When either situation above occurs, the electrician ensures that a grounding electrode conductor connects to the grounded service conductor at the new service disconnect as required in Section 250.24(A), and typically modifies the existing service panel to isolate grounded conductors from contact with the metal enclosure and separates them from equipment grounding conductors in accordance with Sections 250.24(B) and 250.142(B) since the existing service panelboard is no longer considered service equipment; it is now feeder supplied. Modifying a listed electrical service panel often warrants the need for a 3^rd party field evaluation of the modified equipment.

For the above situations, many jurisdictions allow the service conductors or cable to remain as a feeder but the absence of an equipment grounding conductor in the existing branch circuit wiring method results in further code violations created if an electric range, wall-mounted oven, counter-mounted cooking unit, or clothes dryer exists and is fed directly from the existing service panel (now a subpanel).

In past editions of the NEC^®, the exception to Section 250.140 allowed an existing SE cable branch circuit supplying an electric range, wall-mounted oven, counter-mounted cooking unit, or clothes dryer to remain without an equipment grounding conductor (using the grounded conductor instead to ground the appliance frame) if the branch circuit ran straight to the service equipment. The scenarios mentioned above would create a situation where the language in the exception would no longer apply, and in turn, the only code compliant remedy would be to replace the existing 3-wire branch circuit supplying the appliance with a new branch circuit equipped with both a grounded conductor and an equipment grounding conductor.

In the 2023 NEC^®, the previous exception in Section 250.140 was revised into positive text and expanded to provide relief for situations where existing 3-wire branch circuits supplying an electric range, wall-mounted oven, counter-mounted cooking unit, or clothes dryer originate in equipment that previously served as service equipment but is now feeder supplied.

The revised 2023 code language in Section 250.140(B) only applies to existing branch-circuit installations serving electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlets or junction boxes that are part of the circuit. For these existing installations, if an equipment grounding conductor is not present in the outlet or junction box of the range or dryer, the frame of the appliance is permitted to be connected to the branch circuit grounded conductor if all the conditions in Section 250.140(B)(1), (2), and (3) are met and the grounded conductor complies with either 250.140(B)(4) or (5).

Section 250.140(B)(4) covers installations where the grounded conductor of the branch circuit is insulated, or the grounded conductor is uninsulated, and part of a Type SE service-entrance cable and the branch circuit originates at the service equipment.

Section 250.140(B)(5) covers installations where the grounded conductor of the branch circuit is part of a Type SE service-entrance cable that originates in equipment other than a service. The grounded conductor must be insulated, or field covered (within the enclosure where it originates) with listed insulating material, such as tape or sleeving to prevent contact of the uninsulated grounded conductor with any normally non-current-carrying metal parts.

Below is a preview of the NEC^®. See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2023 NEC^® edition of NFPA 70.