We originally posted this article on December 20, 2018. Since that time, we received great feedback. In this updated article, we are going to cover the purpose of the emergency power off (EPO) switch, NFPA 70, and 110 requirements. Some AHJ surveyors have stated the manual stop station should be located in a “remote” area some distance away from the enclosure, while others have said, there is no specific location stated other than “outside” the room housing the prime mover.
“Emergency Power Off” or “EPO”
An EPO or “emergency power off” is a control mechanism for an emergency power supply (EPS) or “generator” intended to disconnect power and shut down the EPS. It’s a safety mechanism in case the primary disconnect device is not readily accessible due to a fire or other unsafe condition. In an emergency, firefighters will use the EPO as a quick way to ensure others will not be exposed to dangerous voltages and eliminate electricity as a source of ignition.
Most activations of the EPO are unintended. Therefore, any EPO system must be designed for any possibility of accidental activation and must minimize any reason for activation other than a life-threatening emergency. Most activations are a human error — unintentional activation during maintenance, mistaken for the wrong button, etc.
The 2017 edition of NFPA 70 (NEC®) states a generator will have the means to disconnect from all associated conductors and the ability to shut down the prime mover. This method is not the same as shutting down the generator during normal operation. The purpose of this requirement is for emergency use only.
If the main disconnect device is not readily accessible, the Emergency Power Off switch (or button) provides a means to disconnect the power and shut down the prime mover from another location. Section 445.18 of the NEC® covers disconnection means and shutting down of the prime mover.
445.18 (A) Disconnecting Means.
Generators other than cord-and-plug-connected portable shall have one or more disconnecting means. Each disconnecting methods shall simultaneously open all associated ungrounded conductors. Each disconnecting means shall be lockable in the open position in accordance with 110.25.
445.18 (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 15kW 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).
445.18 (C) Generator 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.
In 2017 the Centers for Medicare and Medicaid Services (CMS) adopted NFPA 99, Health Care Facilities Code®, 2012 Edition. NFPA 99 references NFPA 110, Standard for Emergency and Standby Power Systems, 2010 edition. In the 2010 edition of NFPA 110, all installations are required to have a remote manual stop station located outside the room housing the prime mover (engine) and labeled.
NFPA 110, 2010 Edition
184.108.40.206* All installations shall have a remote manual stop station of a type to prevent inadvertent or unintentional operation located outside the room housing the prime mover, where so installed, or elsewhere on the premises where the prime mover is located outside the building.
220.127.116.11.1 The remote manual stop station shall be labeled.
NFPA 110, 2019 edition
18.104.22.168 All installations shall be provided with at least one remote emergency stop switch for each prime mover.
22.214.171.124.1 The remote emergency stop switch shall be located outside the room housing the prime mover or exterior enclosure and shall be permitted to be mounted on the exterior of the enclosure.
126.96.36.199.2 Provisions shall be made so access is limited to qualified persons.
188.8.131.52.3 The remote emergency stop switch shall identify the prime mover it controls.
If you read the 2010 edition paragraphs above and compare to the 2019 edition, you will see the addition of “shall be permitted to be mounted on the exterior of the enclosure.” As you may know, most generators located outside within an enclosure come with an EPO switch mounted on the outside of the enclosure. Since the 1980’s most manufacturers deliver the new emergency power supply with the EPO installed. However, this has raised some questions in the health care community on what the CMS is allowing.
After receiving several emails from students regarding placement of the EPO, we sent a question to the Centers for Medicare & Medicaid Services. “Is the CMS now disallowing remote manual stop stations from being located on the outside of a generator enclosure, located outside of a building?”
Answer: “CMS’s longstanding interpretation is that a manual stop needs to be “remote” from the generator as prescribed by 2010 NFPA 110, 184.108.40.206. As such, to be “remote,” a manual stop could not be located on the generator housing.”