How are 2023 NEC generator emergency stop requirements different?
Overview
The prime mover generates the mechanical energy required to drive the electricity generating element of a generator. However, it is particularly susceptible to mechanical stresses and requires protection using an emergency stop mechanism. These mechanisms are outlined in Section
445.19 of the 2023 edition of the NEC, which now permits the emergency stop switch to be mounted on top of the enclosure of certain generators, provided proper labeling is utilized. This modification ensures that all emergency stop switches are situated in known and accessible locations.
Applying the 2023 Code
Generators serve as a dependable power source for both commercial and residential buildings during outages, emergencies, and in remote areas where grid power is unavailable. They also serve as crucial backups for critical systems in hospitals, data centers, and manufacturing, ensuring continuous operation. The prime mover, whether a diesel, gas engine, or turbine, is an essential component of any generator as it converts fuel into the mechanical energy needed to generate electricity. However, being a complex system with numerous moving parts, the prime mover is susceptible to mechanical stresses such as vibrations, overloading, overheating, and wear on components. These factors can quickly degrade its efficiency and longevity. To prevent damage and ensure safety, an emergency shutdown feature, like a switch, is vital for prime movers. This mechanism halts the prime mover immediately upon detecting faults like overheating or over-speeding, thus safeguarding both the prime mover and the generator, minimizing risks to the home, and its occupants.
In previous editions of the NEC, Section 445.18(B), (C), and (D) detailed the requirements for installing such emergency shutdown mechanisms in accessible locations. However, in the 2023 edition, these guidelines were relocated to a new Section 445.19, dedicated solely to emergency shutdown mechanisms. Additional provisions were also added which now allow for mounting emergency stop switches on the exterior of generator enclosures, especially for one- or two-family residences or generators exceeding 15 kW installed in other locations. These updates enhance user understanding when installing emergency stop devices for generators with various uses, ratings, and locations.
What’s New for the 2023 NEC?
The table below presents a comparison between the 2020 NEC and the 2023 NEC regarding Sections 445.18 and 445.19, respectively.
2020 NEC |
2023 NEC |
| 445.18 Disconnecting Means and Emergency Shutdown
(B) Emergency 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. © Remote Emergency Shutdown Generators with greater than 15 kW rating shall be provided with a remote emergency stop switch to shut down the prime mover. The remote emergency stop switch shall be located outside the equipment room or generator enclosure and shall also meet the requirements of 445.18(B)(1) and (B)(2). (D) Emergency Shutdown in One- And Two-Family Dwelling Units For other than cord-and-plug-connected portable generators, an emergency shutdown device shall be located outside the dwelling unit at a readily accessible location.
|
445.19 Emergency Shutdown of Prime Mover
(A) General 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. (B) Remote Emergency Shutdown For other than one- and two-family dwelling units, generators with greater than 15 kW rating shall be provided with a remote emergency stop switch to shut down the prime mover. The remote emergency stop switch shall be located outside the equipment room or generator enclosure at a readily accessible location and shall also meet the requirements of 445.19(A)(1) and (A)(2). The remote emergency stop switch shall be permitted to be mounted on the exterior of the generator enclosure. The remote emergency stop switch shall be labeled Generator Emergency Shutdown, and the label shall meet the requirements of 110.21 (B). (C) Emergency Shutdown in One- And Two-Family Dwelling Units For other than cord-and-plug-connected portable generators, an emergency shutdown device shall be located outside the dwelling unit at a readily accessible location and shall also meet the requirements of 445.19(A)(1) and (A)(2). An emergency shutdown device mounted on the exterior of the generator enclosure shall be permitted to satisfy the requirements of this section. The shutdown device shall be marked as the Generator Emergency Shutdown, and the label shall meet the requirements of 110.21 (B)). |
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