Article 645

[dnbob]

I have read many posts as well as article 645 (NEC2011)

I am unclear when article 645 applies, and when it doesn't, based on previous posts

I am trying to understand the rules for a data center for a local utility company. I can't think of any wiring that would not be a chapter 3 wiring method. I assume with some help on definitions, that this would resolve the answer as to whether the disconnecting means would be required per 645.10. The drawings I have seen show this, but only disconnect the CRAC units, not any other power.

Thanks,

Bob

 

[iwire]

It only applies if you want it to apply.

In other words if you use all chapter 3 wiring methods there is never a reason to go into 645.

On the other hand if you want to use cords instead of chapter 3 methods than 645 will have to be followed.

 

[dnbob]

Ok,

So if I do not use PVC conduit under the raised floor, for example, then I would not need the 645.10 disconnect?

If I install a duplex receptacle under the raised floor using EMT, but then plug in the IT equipment with a power-supply cord, I now need to comply with all of article 645?

 

[GoldDigger]

It only applies if you want it to apply.

In other words if you use all chapter 3 wiring methods there is never a reason to go into 645.

On the other hand if you want to use cords instead of chapter 3 methods than 645 will have to be followed.

Specifically,

645.4 Special Requirements for Information Technology Equipment Room. This article shall be permitted to provide alternate wiring methods to the provisions of Chapters 1 through 4 for power wiring, 725.154 for signaling wiring, and 770.113(C) and Table 770.154(a) for optical fiber cabling when....

If it had said "provides replacement wiring methods", you would have to choose globally for the room which to use. But since it provides alternates, you can mix and match as long as the conditions for application of 645 continue to apply. If you bring in a Chapter 3 wiring method in a way that violates the preconditions for 645 (such as supplying or carrying unrelated circuits, or not having 645.10 disconnecting means), you can no longer use any 645-only methods in that room.

Or, more tersely and compactly, what iwire said.