Weekly digest #138: generator news

Portable generators on jobsites: what the 2023 NEC actually requires

Portable generator use on construction sites keeps tripping up crews during inspection. NEC 590.6(A)(3) now allows listed cord sets or devices with GFCI protection integral to the generator to satisfy ground-fault protection for 15A, 20A, and 30A 125V and 125/250V receptacle outlets that are part of a portable generator rated 15 kW or less. If the generator does not have integral GFCI, you need listed GFCI cord sets at the outlets.

Read 445.20 carefully. It requires GFCI protection for all 125V, 15A, 20A, and 30A receptacles on portable generators rated 15 kW or less. This is non-negotiable on temporary installations, and inspectors are looking for it.

• Check the generator nameplate for integral GFCI marking before plugging tools in.
• If no integral GFCI, deploy listed GFCI cord sets at every receptacle in use.
• Document the configuration in your daily safety brief, especially on prevailing wage jobs.

Bonding the frame: the question that never dies

Whether to bond a portable generator frame to a grounding electrode is still the most common call we get on generator jobs. NEC 250.34 is clear. A portable generator is not required to be connected to a grounding electrode if the generator supplies only equipment mounted on the generator, cord-and-plug-connected equipment through receptacles on the generator, or both, and the non-current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame.

Translation: driving a ground rod at the jobsite is almost never required for a true portable unit. The frame itself serves as the grounding reference. This changes the moment the generator becomes a separately derived system feeding a structure through a transfer switch.

Field tip: If an inspector insists on a ground rod for a portable unit serving only cord-connected loads, pull up 250.34 on your phone. Ninety percent of the time the conversation ends there.

Optional standby systems: transfer switch placement and the neutral problem

Residential standby installs are booming after the storm season, and the neutral-switching question comes up on every service call. NEC 702.11 governs optional standby systems. The transfer equipment must be listed, designed for the purpose, and prevent inadvertent interconnection of the normal and alternate sources.

When the generator is a separately derived system, the neutral must be switched and the generator gets its own grounding electrode connection per 250.30. When the generator is not a separately derived system (common with solid neutral transfer switches), do not switch the neutral, and do not bond neutral to ground at the generator. Bonding it in both places creates parallel neutral paths and objectionable current on equipment grounding conductors.

• Verify whether the transfer switch is 3-pole (switched neutral) or 2-pole (solid neutral) before commissioning.
• Remove the bonding jumper at the generator if the neutral is solid through the transfer switch.
• Label the service disconnect and transfer equipment per 702.7 so the next electrician is not guessing.

Listed vs. field-built: inlet boxes and interlock kits

The budget fix of a generator inlet box with a panel interlock kit is fine, provided both are listed for the application. NEC 110.3(B) requires equipment to be installed and used in accordance with instructions included in the listing or labeling. Most interlock kits are panel-specific, and mixing brands voids the listing.

On the inlet box, the conductors between the inlet and the panel are feeders, sized per 445.13 at not less than 115 percent of the nameplate current rating. Do not size these conductors to the breaker only. The generator output rating drives the calculation.

Field tip: Photograph the interlock kit manufacturer and part number before you button up the panel. When the homeowner calls three years later about nuisance tripping, you will thank yourself.

Large stationary units: fuel, ventilation, and working space

Commercial diesel and natural gas standby installs pull in several articles at once. NEC 445.18 covers disconnecting means and shutdown of prime mover, and the 2023 cycle clarified that the disconnect must be lockable in the open position per 110.25. Placement matters: the disconnect must be within sight of the generator or capable of being locked open.

Working space per 110.26 is frequently compromised on rooftop and pad-mount installs. The 36-inch minimum depth in front of the control panel and disconnect is measured from the live parts, not from the enclosure door. Fuel line routing and exhaust clearances are governed by NFPA 37 and manufacturer instructions, not the NEC, but the AHJ will check both.

• Confirm the generator disconnect is lockable in the open position and tagged.
• Measure working space from live parts, not cabinet faces.
• Coordinate with the mechanical contractor on exhaust termination before setting the pad.

Load calculations for standby: do not guess

Undersized generators are the number one callback on residential standby work. NEC 702.4(B) allows automatic or manual load management, but the generator must have adequate capacity for the load it is connected to serve. For a whole-house install without load shedding, run the full 220.82 or 220.83 calculation and size accordingly.

When using a load-shedding device, document which circuits are managed and which are always on. The AHJ may ask for the load calculation worksheet at final, especially on 200A services with 22kW units that look undersized on paper.

• Pull the panel schedule and run 220.82 before quoting the job.
• Specify the load management device by model number on the permit drawings.
• Leave the calculation with the homeowner in the permit packet.