EPO question - data center


I have PDUs going in a data center. The owner is asking to EPO them at the units. Is this a violation of any codes? I thought that you had to cut power before it enters the space by shunt tripping the breaker or killing the UPS, but I can't find anything that says that.

Also, looking through the forum a little bit I'm reading some posts saying that EPOs are not even required and that the whole NEC 645 is optional. Can someone give me some direction here? This has been an ongoing discussion in my office and I'd like to get some advice from someone with experience with this.



Senior Member
I'm expecting you'll get more and varied responses.

You have to state what code cycle you are on (2005 NEC). 645.1 scope says it applies to "IT Rooms". So if you are designated or claim to comply with IT room requirements, it may be mandatory.

Then 645.4 says "this article shall apply provided" which appears to be voluntary compliance language.

IMO, it is a choice the owner makes and then represents out to their third parties, insurers, reinsurers. If the owner says "we meet the standards required of IT Rooms", they are saying they comply with all of 645 requirements including the EPO and are allowed the more lenient wiring methods.

IMO, the owner may choose to say it's "not an IT Room". It is something the owner considers and gets approval from the AHJ. One difference is the under raised floor wiring. Not an IT room is 300.22 ( C ) 1 plenum rated methods, an IT room is 300.22 ( D ) and the EPO.

645.4 has a lot of other expensive requirements like secured restricted access, no normal occupancy, only maintenance and security access, fire dampers and ductwork isolated from the habitable spaces.

If you are in a large IT room and have magnetic tapes, you should look up the burn characteristics of magnetic tapes. I was surprised when I did. If you have magnetic tapes, there may be a third party requirement to have a complying "IT Room".


Staff member
Article 645 is optional but is often used because it permits wiring methods that are typically not permitted. Even with the added protections/costs required by using Article 645 the optional wiring methods can provide greater flexibility and cost savings.


every datacenter ive wired has had epo's for each rack often there were two a 480V 3? epo and a 48V dc standby system at each 48Urack space .these epo were often handeling eight 4.1kw pem each