#10 wire on 100A breaker

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hill900505

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Hello,
I am running into a potential issue here and would like to get some advice, I am running a #10 wire off a 100A breaker to feed the relays to measure the voltage on A B and C phase. The relay is the last device along the line. This will be a code violation, if I add a 15A breaker inside the box where relay is located (Say, relay to 15a breaker to 100a breaker) will this meet the code requirement?
 
hill900505 said:
Hello,
I am running into a potential issue here and would like to get some advice, I am running a #10 wire off a 100A breaker to feed the relays to measure the voltage on A B and C phase. The relay is the last device along the line. This will be a code violation, if I add a 15A breaker inside the box where relay is located (Say, relay to 15a breaker to 100a breaker) will this meet the code requirement?
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It's a violation. The derated ampacity of the conductor must be greater than the next size down breaker which is protecting it, and a #10 doesn't even come close to 90A. The breaker on the other end (at the relay) doesn't matter.
 
The tap rules in 240.21 determine if a smaller size wire can be connected to a larger breaker. It all depends on the distance between the 100A breaker and the 15 amp breaker, and some other things.

But how are you connecting the #10 wires to the 100A breaker? Are they double lugged with another wire that the load? That could be a code issue also.
 
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