Branch breaker less then nameplate rating?

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ahladas

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Highly featurable equipment (e.g. large computers) will typically have nameplate ratings based on their maximum configuration. The actual configuration may be much less then this rating. Assuming the connector and flexible cord are rated for the nameplate rating, is there anything in the NEC that would prohibit installing a breaker less then the nameplate rating (I'm talking dedicated feed here)?

Seems to me since the distribution is protected, so the answer would be yes.
 
NEC 110.3(B), 110.9&10 seems to prohibit branch wiring, or OCD's rated less than nameplate ratings.
 
Hmm, could be my '96 NEC is dated. In the '96 NEC 110-9 & 10 don't really discuss this. 100-3b is a good reference however, it would appear if the equipment labeling were appriopriate, it would be permitted to use a smaller breaker then nameplace.
 
Perhaps 210.23(a)(1) would apply. This would seem to say that if this is a cord and plug connected equipment it cannot exceed 80% of the branch circuit rating.

The branch circuit rating is determined by the size of the OCPD protecting the circuit. See 210.3

Pete
 
I'm trying to get the biggest difference possible between the main and branch breakers to allow better fault coordination. I work for a manufacturer of large computers. We have one model that is rated for 60A, but only 5% of the machines are configured this way. 80% of them would work fine on a 30A circuit.

My new NEC is on order, the '96 does'nt have a subsection (1) in 210.23(a). But the 80% derating rule has been the one I think may prevent it. We have seen installations where the electrician did this (installed a smaller breaker then nameplate), but just because it happens in a few places does'nt mean it meets the NEC.
 
ahladas said:
I'm trying to get the biggest difference possible between the main and branch breakers to allow better fault coordination. I work for a manufacturer of large computers. We have one model that is rated for 60A, but only 5% of the machines are configured this way. 80% of them would work fine on a 30A circuit.

My new NEC is on order, the '96 does'nt have a subsection (1) in 210.23(a). But the 80% derating rule has been the one I think may prevent it. We have seen installations where the electrician did this (installed a smaller breaker then nameplate), but just because it happens in a few places does'nt mean it meets the NEC.
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By 80% rule are you referring to the requirement that the conductor ampacity
and OC device rating may not be less that 125% of the continuous load?
You say the most of you equipment will work using a 30 breaker. If the name plate on the equipment provide a ampere load rating you will have to use a
breaker that conforms to 210.20 which requires the 125% rule.
If you main breaker and branch ckt breaker both have an instantaneous
setting, it will be very difficult to coordinate the two even if you are using a 60 or 30 amp breaker.
 
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