Can I install a larger breaker than the feed breaker in a subpanel?

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iwire said:
That flies in the face of every installation over-sized for voltage drop.
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No it doesn't. I think you're thinking of it backwards. If a put #4 on a 30A breaker because of voltage drop, the 30A is protecting the #4 at its point of supply. If I put #10 on 50A breaker (ignoring motors, etc.) Then the 50A breaker is not protecting the #10 at its point of supply.
 
david luchini said:
If I put #10 on 50A breaker (ignoring motors, etc.) Then the 50A breaker is not protecting the #10 at its point of supply.
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You and I both know that section is about putting the OCPD ahead of the conductors. It is not about limiting in the way you are trying to apply it.
 
david luchini said:
The branch circuit breaker is the point of supply in the op's specific circuit. The same would apply to a feeder.
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where does it say that in the code?

the term source of supply is used WRT to disconnecting means.

Disconnecting Means. A device, or group of devices, or
other means by which the conductors of a circuit can be
disconnected from their source of supply.
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does this mean it can only interrupt a branch circuit to be considered a code compliant disconnecting means?
 
petersonra said:
where does it say that in the code?

the term source of supply is used WRT to disconnecting means.



does this mean it can only interrupt a branch circuit to be considered a code compliant disconnecting means?
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Not source of supply...point of supply is with respect to location of overcurrent protection...in 240.21.
 
For those who think it is illegal. Would you also say it is illegal feed a sub panel in your garage that is main lug only with 60 amps and put 10 20 amp breakers in it? Because it is not.
 
Also, how about if I put a subpanel in my shop, w/ a 100 A breaker as the disconnect, but use a 90 amp breaker in the main panel feeding it, since the ampacity of the wire feeding it doesn't support 100 A.
 
iwire said:
And the 30 amp breaker protects the conductors in this case.

No violation, just odd.
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The feeder protection is for the feeder conductors ... When he installs a 50A CB at the sub panel that Branch Circuit has a Breaker not ratted to protect the branch circuit conductors . That is where he is wrong even though the feeder is protected at 30A .

I would call it OK if you installed the 50A at the sub panel as a main cb used as a switch and then installed a 30A CB for the branch circuit .



Don
 
Barbqranch said:
Also, how about if I put a subpanel in my shop, w/ a 100 A breaker as the disconnect, but use a 90 amp breaker in the main panel feeding it, since the ampacity of the wire feeding it doesn't support 100 A.
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I would call that OK as the feeder is protected at 90A so the 100A cb becomes a disco .

The Branch CB's would have to protect the Branch Circuit Conductors .





Don
 
donaldelectrician said:
The feeder protection is for the feeder conductors ... When he installs a 50A CB at the sub panel that Branch Circuit has a Breaker not ratted to protect the branch circuit conductors . That is where he is wrong even though the feeder is protected at 30A .

I would call it OK if you installed the 50A at the sub panel as a main cb used as a switch and then installed a 30A CB for the branch circuit .



Don
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So basically he has a correctly wired 30 amp circuit but the addition of a GFCI device into the circuit has caused an NEC violation.

I am not seeing the logic in this in the least and I don't believe that is what 240.21 is restricting.



That section is simply making a distinction between conductors being protected at the supply end vs the load end as tap conductors are.
 
iwire said:
So basically he has a correctly wired 30 amp circuit but the addition of a GFCI device into the circuit has caused an NEC violation.

I am not seeing the logic in this in the least and I don't believe that is what 240.21 is restricting.



That section is simply making a distinction between conductors being protected at the supply end vs the load end as tap conductors are.
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Do you at least agree that in the OP's scenario the 50A is the branch circuit breaker but when it is removed the 30A becomes the branch circuit breaker?

I have not been able to find a code section, other than the ones for taps, which restricts where the conductor protection has to be located.
It is also possible that the 50A breaker could be considered supplemental OCPD, leaving the 30A breaker as the branch protector, as long as no other circuits connect to the 30A "feeder" breaker.
 
GoldDigger said:
Do you at least agree that in the OP's scenario the 50A is the branch circuit breaker ...
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I do not.
If the device does not adequately protect the conductor then it is not an OCPD for those conductors and for all practical purposes does not exist. The 30A breaker is the branch circuit breaker.

The NEC generally addresses the current installation, what someone may do in the future is not typically a factor (e.g. there is nothing in Section 240 that deals with preventing a protective device from being changed)
 
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