National Electrical Code Articles and Information
National Electrical Code Top Ten Tips: Article 445 -- Generators
by Mark Lamendola
Based on the 2020 NEC
Please note, we do quote from copyrighted material. While the NFPA
does allow such quotes, it does so only for the purposes of education
regarding the National Electrical Code. This article is not a substitute
for the NEC.
A generator is basically a motor operating in reverse. Instead of using electricity to spin the motor and thus do work, another force is used to do the work of spinning the motor to produce electricity. This can be a steam-powered turbine (the heat for creating the steam is produced through burning coal, controlling a nuclear chain reaction, etc.), a piston-driven engine fueled by kerosene, a wind turbine, etc.
These are the 10 NEC Article 445 items we deem most important, based
on the pervasiveness of confusion and the potential costs of same.
- Article 430 also applies. Well, part of it anyhow. Generators must meet the requirementes for motors in 430.14 [445.10]. Those have to do with location factors, such as having adequate ventilation and adequate room for maintenance. This doesn't mean three feet of open space in front of equipment (a common misinterpretation of the OSHA requirements). It means there is enough room for maintenance personell and their equipment (including a maintenance cart and including lifting equipment for component replacement) to safely perform testing, maintenance, and repair.
- Generators also, like motors, must be suitable for the locations in which they are installed [445.10]. That includes such factors as temperature and dampness.
- Manufacturers are required to provide a nameplate that contains several mandated bits of information [445.11]. This is important for the installer, not because you have to comply with this requirement (the manufacturer does) but because you need this information to do a correct installation job. And there it is, right on the nameplate. Take a photo of that nameplate before installing the generator.
- The overcurrent protection requirements come in five different flavors: constant-voltage generators, two-wire generators, 65V or less, balance sets, and three-wire direct-current generators [445.12].
- You might not be required to provide the overcurrent protection described in 445.12. There's an Exception note at the end of this Section. Basically, if it's safer to run the generator to failure you can let it do that if you provide a supervised alarm and the AHJ signs off on this arrangement.
- The conductors running from the generator to the first distribution devices containing overcurrent protection must have an ampacity of at least 115% the nameplate rating of the generator [445.13(A)]. You may wish to step up the conductors to the next size above meeting this minimum; that is a cheap way to improve system performance.
- You can used tapped conductors from the load side if your installation meets specific circumstances per 445.13 (B). You cannot use tapped conductors for portable generators rated 15.5KW or less where field wiring connections aren't acessible.
- Where field wiring passes through an enclosure, conduit box, or barrier, you must use a bushing to protect the conductors from the edges of the opening [445.16]. Tip: If you drill a hole, deburr it rather than relying on the bushing to also protect from the burrs. Where possible, file sharp edges away. Bushings can wear or pop out (due to vibration or other factors), so don't use them to cover sloppy work. Use them as an additional measure of protection.
- Each generator must have a provision for shutting down the prime mover and it must require a mechanical reset (as opposed to an automatic one) to restart the generator[445.18(B)].
- GFCI protection requirements differ, depending upon whether you have an unbonded (floating) neutral or bonded neutral [445.20]. If it's bonded, all 125V receptacles rated 15A or 20A must be GFCI-protected. If it's unbonded, all 125V receptacles rated 15A or 20A must be GFCI-protected but only if the system also has at least one 125V/250V receptacle. The logic behind this difference is unclear. It would be prudent and inexpensive to ensure that all 125V receptacles rated 15A or 20A are GFCI-protected regardless of whether the neutral is bonded or not.