Definition

Emergency Power Off (EPO) button

The Emergency Power Off (EPO) button, also called an EPO switch or EPO panel, is a safety measure for quickly disconnecting electrical power to a particular piece of equipment, or to an entire facility, in the event of an emergency. The button allows all power, including uninterruptable power supplies (UPSs) and batteries to be shut down safely from a central location.

EPO buttons can be found in places such as manufacturing plants, telecommunications facilities and information technology (IT) data centers. The goal of shutting down power in a centralized manner is to limit damage in the event of a disaster and make it safer for rescue personnel deal with the emergency.

The history of the EPO button dates back to a 1959 fire at The Pentagon that caused over $6 million in damages. Three years later the National Fire Protection Association (NFPA) released its first Standard for the Protection of Electronic Computer Systems, which became known later on as NFPA 75. While NFPA 75 is technically a recommended standard, it is not required by law unless adopted by the local jurisdiction. Even then, it may be negotiable with the Authority Having Jurisdiction.

In contrast, NFPA 70, more commonly known as the National Electrical Code (NEC), is a mandatory code. Although Article 645 defines the circumstances under which an EPO button is required, the definition is often misinterpreted. In most jurisdictions, the EPO switch is not automatically mandated in data centers unless the owners and designers want to take advantage of certain options such as loose power whips under air plenum floors or non-plenum cable.

The specific requirements around an EPO button's size, placement and accessibility vary and depend on local jurisdiction. Historically, EPO buttons had to be installed at every exit door. However, since the 2011 version of the NEC, it is possible to put a single EPO switch in a nearby room with approval of the code inspector and the fire marshal.

Data center teams who do install an EPO button should clearly mark the button's presence, and install it under a clear, lift-cover box, preferably with an integrated alarm, to avoid the risk of somebody hitting it accidentally, and causing unintentional downtime. This has historically been a major cause of data center outages, usually when the button was mistaken for a door release.

EPO button vendors include APC by Schneider Electric and STI.

This was last updated in August 2017

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