445.18 Disconnecting Means and Shutdown of Prime Mover.
Code Change Summary: Requirements for generator disconnection have changed.
In the 2014 NEC®, Section 445.18 was restructured to provide clarity to the rules on generator disconnection. To many, the rules were still confusing.
In the 2017 NEC®, this section underwent significant reconstruction once again in order to bring additional clarity. The text was formatted into three subsections which differentiate between the rules pertaining to the actual disconnecting means, prime mover (engine) and generators operating in parallel (common in hospitals and large commercial facilities). Here are a few of the highlights:
Subsection A Disconnecting Means: Each generator must have a disconnect that simultaneously opens all associated ungrounded conductors and is lockable per 110.25.
Subsection B Shutdown of Prime Mover (engine): There must be a way to shut down the engine. Once shutdown, the shutdown device must render the engine incapable of restarting automatically and to restart the engine there must be some kind of manual reset. This device can also function as the disconnect required in subsection A as long as it can be locked in the open position. Generators rated over 15 kW require an extra shutdown means for the engine (in addition to the main shutdown device mentioned at the beginning of subsection B). This additional shutdown means must be located outside the equipment room or generator enclosure and must also meet the requirements of 445.18(B)(1) and (B)(2).
Subsection C Generators Installed in Parallel: If generators operate in parallel with each other, the disconnect required in 445.18(A) must be able to isolate the generator output terminals from the paralleling gear (this is so that the generator can be serviced without the fear of the paralleling gear energizing the generator being serviced). There is no requirement on where this disconnect must be located.
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 2017 NEC® edition of NFPA 70.
2014 Code Language:
445.18 Disconnecting Means Required for Generators.
Generators shall be equipped with a disconnect(s), lockable in the open position by means of which the generator and all protective devices and control apparatus are able to be disconnected entirely from the circuits supplied by the generator except where the following conditions apply:
(1) Portable generators are cord- and plug-connected, or
(2) Both of the following conditions apply:
a. The driving means for the generator can be readily shut down, is rendered incapable of restarting, and is lockable in the OFF position in accordance with 110.25.
b. The generator is not arranged to operate in parallel with another generator or other source of voltage.
2017 Code Language:
445.18 Disconnecting Means and Shutdown of Prime Mover.
N (A) Disconnecting Means. Generators other than cord-and plug- connected portable shall have one or more disconnecting means. Each disconnecting means shall simultaneously open all associated ungrounded conductors. Each disconnecting means shall be lockable in the open position in accordance with 110.25.
N (B) Shutdown of Prime Mover. Generators shall have provisions to shut down the prime mover. The means of shutdown shall comply with all of the following:
(1) Be equipped with provisions to disable all prime mover start control circuits to render the prime mover incapable of starting
(2) Initiate a shutdown mechanism that requires a mechanical reset
The provisions to shut down the prime mover shall be permitted to satisfy the requirements of 445.18(A) where it is capable of being locked in the open position in accordance with 110.25.
Generators with greater than 15 kW rating shall be provided with an additional requirement to shut down the prime mover. This additional shutdown means shall be located outside the equipment room or generator enclosure and shall also meet the requirements of 445.18(B)(1) and (B)(2).
N (C) Generators Installed in Parallel. Where a generator is installed in parallel with other generators, the provisions of 445.18(A) shall be capable of isolating the generator output terminals from the paralleling equipment. The disconnecting means shall not be required to be located at the generator.