# Size of Circuit Breaker feeding a sub panel

The sketch below is for a new Panel "W" that is being fed from the existing main distribution panel. Panel "W" has a 150 AMP circuit breaker feeding it from the main panel. Panel "W" is 100 AMP.

Question: Does the circuit breaker have to be maximum 100 AMP (to be the same size as Panel "W" or less) or can it be larger in size (i.e. 150 AMP) and still be ok? Electrical code section please !

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Original Post
"408.36 Overcurrent Protection.
panelboards...shall be protected by an overcurrent protective device having a rating not greater than that of the panelboard."

In the 2005 NEC protection "not greater than that of the panelboard" applies to both power and lighting/appliance panelboards. As accepted for the 2008 NEC, there will no longer be two types of panelboard.redwood@codecheck.com
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Thanks Redwood!

1) So the circuit breaker feeding Panel "W" can not be larger than 100 AMP in accordance with NEC 480.36.

2) In regards to the size of the electric wires feeding Panel "W", would those wires have to be sized for the circuit breaker feeding Panel "W". In otherwords, if the circuit breaker is 100 AMP, then the wires ampacity should be sized for at least 100 AMP?

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If the sub panel allows the 150a breaker and the breaker feeding that panel from the main adequately protects the feeder the 150a breaker is just a disconnect. I don't see a violation
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Greg-

1) Are you saying if Panel "W" is 100 AMP rated with 100 AMP breaker at the panel, then the circuit breaker at the main may be 150 AMP rated (acting as a disconnect only)?

2) Again, for the wires size in the conduit feeding sub panel "W".....would those wires be sized based on the size of the circuit breaker in the main panel feeding sub panel "W"?

For example, if the circuit breaker at the main feeding Panel "W" is 150 AMP, then the wires in the conduit must be at least size 1/0 (75 deg. column in NEC Table 310-16; Good For 150 amp). IF the circuit breaker is 100 AMP, the wires may be #3 (Good For 100 amp) ??
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"1) So the circuit breaker feeding Panel "W" can not be larger than 100 AMP in accordance with NEC 480.36.

...rk... That is correct...rk...

2) In regards to the size of the electric wires feeding Panel "W", would those wires have to be sized for the circuit breaker feeding Panel "W". In otherwords, if the circuit breaker is 100 AMP, then the wires ampacity should be sized for at least 100 AMP?"

...rk... Correct...rk...

A breaker in panel "W" is optional.
NEC 408.36 allows the feeder ocpd to protect the panelboard.
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If panel W is 100a rated and has a 100a breaker in it the feeder can be larger as long as it is protected at the source.
You can certainly "feeder tap" off another panel from there is it meets the other tap rules.
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