Every three years, the National Fire Protection Association (NFPA) issues a new edition of the NEC. The latest edition of the NEC was in 2017, and it included some changes from the previous 2014 edition. One of the changes introduced under the 2017 NEC was that pertaining to a generator shutdown.
The pertinent provision is located in Article 445. 18, previously entitled “Disconnecting Means Required for Generators.” Under the 2017 NEC, the title was amended to “Disconnecting Means and Shutdown of Prime Movers.” A prime mover is the engine that drives the alternator or the generator. Already, we can see that there is a significant difference between the two editions, but the purpose is the same, which is the proper shutdown and disconnecting means for a generator. The intent here is that all installations shall be provided with a remote guide quit station, to prevent inadvertent or unintentional operation.
The essential difference is the additional requirement for a shutdown means for generators with greater than 15kW rating. This should be located outside the equipment room or generator enclosure and must also meet code requirements under Section 445,18 (B) (1)and (B) (2). When in use, the prime mover or engine can be shut down so that it cannot be restarted without a manual or mechanical reset of the generator start circuits. If there should be an emergency, pushing the stop button or the off switch will immediately shut down the generator. A message on the controller will appear, which will need to be cleared before the generator can be restarted manually again.
If, on the other hand, generators are installed in parallel with other generators, code provisions provide that the generator output terminals shall be capable of being isolated from the paralleling equipment. Again, the disconnecting means is not to be located at the generator.
So both exterior and interior generators are now required to have a second means of shutting down the prime mover, and this second means is remote from the prime mover, i.e., not on the prime mover, its enclosure, or within the room in which the prime mover is located. It may possibly be located on an exterior generator enclosure.
Generator manufacturers have now begun the production of Shutdown Kits so that their standby generators can be code-compliant. There are engine shutdown add-on kits that can be used to bring generators up to code,
What is important to remember is that this amended provision refers to three different and separate rules: that for disconnecting means, the shutdown of the prime mover, and generators installed in parallel. All three should be interpreted separately from each other.
A disconnecting means, for instance, should be equipped for generators that are lockable in the open position. This is not applicable to generators that are cord- and plug- connected, or those with one or more disconnecting means. These exceptions, however, do not apply to the shutdown of the prime mover, and only apply to disconnecting means.
Again all generators should be equipped with a provision to shut down the prime mover, and this shutdown means should be able to disable all the prime mover start control circuits and to render the prime mover incapable of starting. This shutdown must be such that a mechanical reset is required to start the generator again. If a generator has a greater than 15kW rating, then additional shutdown is required outside the enclosure or room in which the generator is housed.
Finally, for generators installed in parallel, the requirement is that the disconnecting means must be able to isolate the generator output terminal from the paralleling equipment.
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