200% Neutral for non-linear loads

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bnbowen@uiuc.edu

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Is it required by the NEC or just good practice to install a 200% neutral for panel feeders where 100% of the load is going to be non-linear in a data center or an "Information Technology Room"? If it is required by the NEC, what section is it in? I've read many posts on this subject and it appears to be good practice/design and not a requirement.
 
It is not required by the NEC and whether it is good design or not, it probably is but, I doubt there would ever be a problem with the neutral conductor if it were sized per the NEC requirements of article 220.

Roger
 
And what Bob said. (I guess we were posting at the same time, I'm just slower :smile:)

Roger
 
In my opinion, non-linear loads are not the big problem they started out to be. Apparently, a lot of effort has gone into the electronics to keep the harmonics to a minimum so as not to cause problems. :smile:
 
I've had inspectors claim that when you over size the neutral then you expect it to be a current carrying conductor. On a 3-phase panel that's now 4 current carrying conductors so the conductors are derated to 80%. I'll point to them where it states that neutrals are exempt and they'll just say it doesn't apply when I oversize the neutral. Just so you know.
 
Mr. Bill said:
I've had inspectors claim that when you over size the neutral then you expect it to be a current carrying conductor. On a 3-phase panel that's now 4 current carrying conductors so the conductors are derated to 80%. I'll point to them where it states that neutrals are exempt and they'll just say it doesn't apply when I oversize the neutral. Just so you know.
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In this case since 100% of loads are non-linear the neutral is already a CCC

(4) Neutral Conductor.
(a) A neutral conductor that carries only the unbalanced
current from other conductors of the same circuit
shall not be required to be counted when applying the provisions
of 310.15(B)(2)(a).
(b) In a 3-wire circuit consisting of two phase conductors
and the neutral conductor of a 4-wire, 3-phase, wyeconnected
system, a common conductor carries approximately
the same current as the line-to-neutral load currents
of the other conductors and shall be counted when applying
the provisions of 310.15(B)(2)(a).
(c) On a 4-wire, 3-phase wye circuit where the major
portion of the load consists of nonlinear loads, harmonic currents
are present in the neutral conductor; the neutral conductor
shall therefore be considered a current-carrying conductor.
 
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