Sub-Panel Breaker

[Roger A. Frost]

Came across a sub-panel with 100 amp breaker. The feed is from main panel is 40 amps which is on breaker. The circuits are all protected by breakers.

Would it make any difference that sub-panel has 100 amp breaker when only 40 amp feed. All the circuits are protected by appropriate breakers.

I find this odd and the panel was probably used and came with breakers already installed.

Appreciate thoughts and input.

[Jeffrey R. Pope]

Often, the 100 amp breaker is simply being used as a disconnect for the distribution panel. This would be the case if the feeders from the service equipment were tied to that breaker.

If the 100A breaker was being used as OCPD for another device, then it is obsolete and indicative of repairs/modifications from unqualified persons. The device will trip the 40A breaker at the service equipment before it will trip the 100A breaker.

[Dale Duffy]

Originally Posted by rfrost

Came across a sub-panel with 100 amp breaker. The feed is from main panel is 40 amps which is on breaker. The circuits are all protected by breakers.

Would it make any difference that sub-panel has 100 amp breaker when only 40 amp feed. All the circuits are protected by appropriate breakers.

I find this odd and the panel was probably used and came with breakers already installed.

Appreciate thoughts and input.

Hi Roger

What size conductor is feeding the 100 Amp Breaker connected to the 40 Amp?

[Roger A. Frost]

Number 8 wire, supplied from 40 amp breaker in main panel.

[Robert Meier]

Originally Posted by rfrost

Number 8 wire, supplied from 40 amp breaker in main panel.

So far so good. Are the lugs on the 100 amp CB listed for #8 conductors?

[Robert J. OConnor]

Originally Posted by Robert Meier

So far so good. Are the lugs on the 100 amp CB listed for #8 conductors?

Good point but likely not a significant issue for an HI if there is a solid connection.

[Roger A. Frost]

Thanks for thoughts. Noted the 100 amp dis-connect as observation that it was over-rated and would not be typically used on 40 amp feed.

[Robert J. OConnor]

Originally Posted by rfrost

Thanks for thoughts. Noted the 100 amp dis-connect as observation that it was over-rated and would not be typically used on 40 amp feed.

I wouldn't say the 100A breaker/disconnect is overrated since the #8 wires are adequately protected in the service panel ... but it may not have been tested for terminating the #8 wire which means there may be a potential for a poor connection, which should be checked if you didn't

JMO & 2-Nickels ...

[Jim Port]

Originally Posted by rfrost

Thanks for thoughts. Noted the 100 amp dis-connect as observation that it was over-rated and would not be typically used on 40 amp feed.

Since it is not needed the rating is irrelevant. Also remember that the 100 amp is the max rating, not a minimum rating. It is serving as a redundant shutoff. You will not find a panel with a 40 amp main unless the panel was being backfeed.