Weekly digest #48: generator news

Why generator news matters this week

Generator installations are climbing. Backup power for homes, portable units on jobsites, and standby systems for critical facilities all carry their own NEC requirements, and 2023 cycle changes plus recent UL revisions have shifted what passes inspection. If you wire generators, this digest covers the rules getting flagged in the field right now.

Three areas dominated this week's discussion: portable generator GFCI requirements under 590.6, optional standby system disconnect rules in 445.18, and grounding decisions for separately derived versus non-separately derived systems per 250.30 and 250.35.

Portable generators on jobsites: 590.6 and OSHA overlap

Temporary power on construction sites still trips up crews. Article 590.6(A)(3) requires GFCI protection for all 125V, 15, 20, and 30 amp receptacles supplying temporary power. If your portable generator has a listed GFCI receptacle factory installed, you are covered. If it does not, you need an in-line GFCI or a GFCI cord set.

The catch is bonded versus floating neutrals. Most newer portable generators ship with a floating neutral so the GFCI inside the generator works correctly when feeding through a transfer switch. Plug a tool directly into a floating neutral generator without a bonding plug, and the GFCI may not trip on a fault. Check the nameplate, check the manual, and know which configuration you are working with.

Field tip: Carry a bonding plug and a plug-in GFCI tester. Two minutes of verification at the generator beats a callback or a shock complaint.

• Floating neutral generator feeding a transfer switch: bond is at the service, do not add a bonding plug.
• Floating neutral generator feeding tools directly: install a bonding plug so the GFCI references ground correctly.
• Bonded neutral generator through a transfer switch: switch the neutral, or you create parallel neutral paths and possible objectionable current under 250.6.

Standby system disconnect: 445.18 changes worth knowing

Article 445.18 was reorganized in the 2020 cycle and refined in 2023. Every generator now needs a disconnecting means that can be locked in the open position, located within sight of the generator or capable of being locked. The disconnect must shut down the prime mover, open the conductors, and disable any remote start signal.

For one and two-family dwellings, 445.18(D) gives you a break: the disconnect can be outside the dwelling at a readily accessible location. That usually means alongside the service disconnect or the transfer switch enclosure. Inspectors are increasingly checking that the remote stop is actually wired and functional, not just labeled.

If you are installing a standby unit at a commercial site, confirm the emergency shutdown per 445.19 is also addressed. A single labeled mushroom button at the entrance often satisfies both, but read the AHJ amendments before you assume.

Grounding: separately derived or not

This is where most generator jobs go sideways. The decision tree under 250.30 and 250.35 hinges on the transfer switch:

1. Three-pole transfer switch (neutral solidly connected through): generator is NOT separately derived. Do not bond neutral to ground at the generator. The bond stays at the service.
2. Four-pole transfer switch (neutral switched): generator IS separately derived. Bond neutral to ground at the generator, install a grounding electrode conductor per 250.30(A)(4), and size the system bonding jumper per 250.30(A)(1).
3. Optional standby with switched neutral: same rules as above. Do not skip the grounding electrode just because the run is short.

The most common violation we see is a bonded neutral portable or standby generator wired through a three-pole switch. That creates a parallel neutral path through the equipment grounding conductor, and you will see neutral current on metal raceways. NEC 250.6(A) prohibits exactly this condition.

Receptacle and inlet rules under 702.12

Article 702 covers optional standby systems, including the manual transfer setups common in residential backup. Section 702.12 was updated to clarify power inlet requirements. The inlet must be listed, rated for the generator output, and the cord assembly between generator and inlet must be no longer than necessary, with strain relief at both ends.

For interlock kits, confirm the kit is listed for the specific panel. A field-fabricated interlock plate is not compliant, even if it looks identical to a listed one. AHJs are red-tagging unlisted interlocks more aggressively this year.

Field tip: Photograph the inlet listing label and the interlock kit listing before closing up the panel. If an inspector questions it later, you have proof.

Quick reference for the week

Pin these to your truck binder or pull them up in Ask BONBON when you are on a generator call:

• NEC 590.6(A)(3): GFCI on temporary 125V, 15/20/30A receptacles.
• NEC 445.18: Generator disconnect, lockable, shuts down prime mover.
• NEC 250.30: Grounding for separately derived systems.
• NEC 250.35: Permanently installed generators, grounding rules.
• NEC 702.12: Optional standby power inlets and transfer equipment.
• NEC 250.6: Objectionable current, the rule that catches double-bonded neutrals.

Next week we will cover EV charger load calculations under 625.42 and the article 220 changes that affect service sizing when a generator and EVSE share a panel. If you have run into a generator inspection issue this week, log it and we will pull the most common ones into a follow-up.