Higher ampere-rated device protected by a lower ampere-rated device

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cohosilver

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A load center on structure ?A? has a 3-pole 100A rated circuit breaker protecting #2awg conductors that are feeding a 200A MCB at a separate structure called structure ?B?. Is this a NEC Code violation? If so, which specific codes?

The continuous load and non-continuous load is not a factor. The total demand for structure ?B? is 30A per phase. The 200A panel at structure ?B? is an existing panel and is presently being fed with a small generator. The generator is being removed and structure ?B? is going to be powered by structure ?A? which is fed by the utility.
 
The 200 amp CB at the end of the feeder is fine. The #2 AWG conductors are protected by the 100 amp OCPD. The 200 amp CB is basically just a disconnecting means.
 
As Rob says, no problems with the 200 amp panel.
If you have not done so, you might review Art 225 and 250.32.
There are a lot of requirements.
 
infinity said:
The 200 amp CB at the end of the feeder is fine. The #2 AWG conductors are protected by the 100 amp OCPD. The 200 amp CB is basically just a disconnecting means.
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Good catch, however, looking at table 310.15, the #2 AWG, assuming copper, is rated at 95A (60 degree column), per 110.14, unless the circuit breaker is rated for use at 100% of its 100A rating.

I'd say the 100A breaker needs to be downsized or the #2 wire upsized unless the CB shows 100% rating.
 
antenna2001 said:
Good catch, however, looking at table 310.15, the #2 AWG, assuming copper, is rated at 95A (60 degree column), per 110.14,
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Most equipment has 75C terminals so we would use the 75 C column.

But that does not mater anyway as a 95 amp rated conductor can be protected with a 100 amp breaker due to 240.4(B).

I'd say the 100A breaker needs to be downsized or the #2 wire upsized unless the CB shows 100% rating.
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It has nothing to do with a 100% rated breaker, in fact normally 3AWG Copper is used for 100 amp feeders / services.
 
antenna2001 said:
Good catch, however, looking at table 310.15, the #2 AWG, assuming copper, is rated at 95A (60 degree column), per 110.14, unless the circuit breaker is rated for use at 100% of its 100A rating.

I'd say the 100A breaker needs to be downsized or the #2 wire upsized unless the CB shows 100% rating.
Click to expand...


Care to explain? The 100 amp OCPD is protecting a either 95 amp or 115 amp conductor depending on some other factors. Even at 95 amps a 100 amp OCPD would be permitted if the load is 95 amps or less.
 
infinity said:
Care to explain? The 100 amp OCPD is protecting a either 95 amp or 115 amp conductor depending on some other factors. Even at 95 amps a 100 amp OCPD would be permitted if the load is 95 amps or less.
Click to expand...

I was wrong. As iwire correctly pointed out, the terminals of most equipment are rated for 75-degree operation; therefore, 110.14(C)(3) permits the set up. Also, as iwire and you point out, the 100A breaker can protect the 95A conductor.

The installation, as far as I can tell is code compliant.
 
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