National Electrical Code Top Ten Tips: Article 645, IT Equipment
Why do we have Article 645? Did the IT (Information Technology) people decide
they felt left out, so they had an article created to make them feel important?
No, that's not it. Article 645 exists because an IT room (which is any room that conforms to NFPA 75) contains hazards not found in non-IT rooms.
- For one thing, an IT room doesn't lose all power just because first
responders shut off the main. The computer equipment is on a UPS, or may
even be on an alternate source such as an emergency generator.
- For another, the raised floors common in IT rooms add
a layer or two of difficulty to reducing the spread of flame and smoke.
And those are only two contributors to the difficulty that IT rooms present
to fire containment and fire response.
Another issue that often inserts itself into the discussion of IT room
requirements is whether the equipment inside it is really IT equipment or if
it's communication equipment. That is, does the equipment fall under Article 645
or under Article 800? The short answer is no matter what equipment is in a room,
if that room conforms to NFPA 75 it's an IT room. You may have operational,
engineering, and reliability issues to sort out if you're jamming different
systems into the same room.
- This article covers the IT equipment and related wiring in an IT room.
Basically, if it's an IT room, this article covers everything in it.
- An IT room is any room that meets the definition presented in NFPA
75:3.3.9; that is, it's any room that contains IT equipment [645.2].
- Any communications penetrations to that room must comply with 800.26
and/or 820.26 (where applicable) 645.3].
- Bond all metallic objects [645.15], for reasons that are detailed in
IEEE-142, and to meet the requirements of Article 250, Part V. This
eliminates differences of potential. And, yes, the non-current carrying
metallic parts of fiber optic cables must also be bonded [645.3(C)].
- Article 645 allows you to use wiring methods that are an alternate
choice to those in Chapters 1 - 4, provided you meet the requirements of
- IT loads are high-harmonic loads. Thus, you don't need to decide whether
a load is continuous or noncontinuous in deciding whether to apply the 125%
rule to IT branch circuits. It applies, regardless of whether the loads are continuous or noncontinuous.
- Only certain cable types are permitted under raised floors. See Table
645-5 for what these cable types are.
- The iconic feature of an IT room is the remote disconnect[645.10] typically mounted near the door of the room. Usually, there's also a sign that sternly warns against operating it unless there's an emergency. As with any disconnect, this should be mounted such that the operator stands to the
right of the switch and pulls down with the left hand to open it. Remember,
this switch is operating under load. You don't want to place a person in the
blast path. The enclosure will mute the blast somewhat, but will not provide
- The remote disconnect must also disconnect the HVAC [645.10(A), and
disconnect the UPS from its loads [645.11].
- For critical operations data systems, remote disconnecting controls
aren't required if the installation meets all the requirements of 645.10(B).