Nec 110.26

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Although I posted this already, I'm doing it again. I really want feedback on this.

We are evaluating three Power Distribution Centers, each will have a 480 Volt MCC on one side of a working space and a 480/277 panel board on the other side. You can't expose live parts in the panel board without taking the cover off, and taking the cover off is a large job.

What should dictate our clearance requirement? NEC 110.26 Condition 2 or 3?
 
While I understand that the NEC wants this to be Condition 3, I don't find any support for this other than the wording in 110.26(A)(1)(c).
Exposed (as applied to live parts). Capable of being inadvertently touched or approached nearer than a safe distance by a person. It is applied to parts that are not suitably guarded, isolated, or insulated.
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Condition 1 — Exposed live parts on one side of the working space and no live or grounded parts on the other side of the working space, or exposed live parts on both sides of the working space that are effectively guarded by insulating materials.
Condition 2 — Exposed live parts on one side of the working space and grounded parts on the other side of the working space. Concrete, brick, or tile walls shall be considered as grounded.
Condition 3 — Exposed live parts on both sides of the working space.
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How is a panel with its cover installed "exposed live parts"?
Yes, I understand that they are concerned about the removal of covers on both sides of the aisle, but the wording does not support this. This is another area where the code rule does not say what the CMP wants it to and the CMP refuses to accept proposals to correct it.
 
I agree with Condition 3. If there's a chance (however remote) that both pieces of equip could have exposed live parts at the same time, then you have to consider both as "live parts".
 
I agree with Don. How is a covered panel considered "Exposed live parts" with the NEC's definitions of exposed.. I guess it is a AHJ issue.
 
kfenn22 said:
I agree with Don. How is a covered panel considered "Exposed live parts" with the NEC's definitions of exposed.. I guess it is a AHJ issue.
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???

Capable of... (Not likely of)
 
jbt260 said:
I agree with Condition 3. If there's a chance (however remote) that both pieces of equip could have exposed live parts at the same time, then you have to consider both as "live parts".
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So back to my comment about signage: If the panel board for example was clearly labelled, ?WARNING Cover must not be removed unless de-energized at the MCC, with Breaker No. XXX, locked and tagged out? - you get the idea.

Example - open pit mining operation where equipment moves and thus must the controls. Containerizing those controls can be a excellent solution for portability. But put gear (<600VAC) across from one another in a container and you may breach condition 3 but comply with 2.

Tags / Signs?
 
110.26 A 1 - "distances shall be measured from the exposed live parts or from the enclosure or opening if the live parts are enclosed.

(2005)



I agree with condition 3
 
don_resqcapt19 said:
While I understand that the NEC wants this to be Condition 3, I don't find any support for this other than the wording in 110.26(A)(1)(c).


How is a panel with its cover installed "exposed live parts"?
Yes, I understand that they are concerned about the removal of covers on both sides of the aisle, but the wording does not support this. This is another area where the code rule does not say what the CMP wants it to and the CMP refuses to accept proposals to correct it.
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When the potential exist, one needs to take it into account as the worst condition. I have seen Condition 2 applied to case like yours where a warning sign was posted to the effect that no simultaneous exposure of live parts on both sides is prohibited.
 
weressl said:
When the potential exist
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I am still in the condition 3 camp however remaining privy to debates. Let me throw another curve in this.

On one side of the space put a feeder breaker supplying the other with a mechanism requiring it is de-energized or racked out to open a door or barrier over it. And further to that, perhaps a finger safe guard could be placed inside of a cheatable breaker mechanism?s compartment if that is the case. (It seems I am tending towards an AHJ situation)

It has actually been a pretty big deal in my experience. Example mining application, MSHA is the AHJ, and there are situations where the volume to accommodate condition 3 can be a detriment in itself (larger span of roof if underground for example). A wider portable structure more dangerous to move is another. There are simply tight spaces where equipment goes, and my intention is to canvas the opinion of those of you in other industries.

The feedback I have received thus far is excellent by the way. Thanks, and I wouldn't mind this thread beating that "three foot rule" vernacular up a bit.
 
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