Minimum Size Breaker for Sub Panel

[rmoewe]

Can someone tell me what the MINIMUM size breaker is to supply a fairly large and full sub panel, (17 breakers, 2 of the 30 amp and the rest 15 and 20 amp breakers). I had one that the Main is not labeled, of course and can not tell what breaker the sub is being fed by. I do know that the supply wire to the sub is only a number 6, which is good for up to a 60 amp breaker. 60 amps does not seem to be big enough, to me.
Thanks, Rick

[Speedy Petey]

Originally Posted by rmoewe

60 amps does not seem to be big enough, to me.

What do you base this on? Have you done a load calculation? Do you know what loads are served by this panel?
What if one 30 is feeding A/C and the other is feeding electric heat? What if the rest are feeding simple general receptacles and lighting?

See what I am getting at? If you've ever done a load calc on a home you'd see the actual demand load is not usually what you would think. It is very typical to have a fully loaded 40 space 200 amp panel with a demand load of under 150 amps.

[Marc D. Shunk]

Originally Posted by rmoewe

Can someone tell me what the MINIMUM size breaker is to supply a fairly large and full sub panel,

Yes, I'd be glad to do that load calc for you, but I'd need a ton more information. Counting breakers is a really goofy way to determine whether the feeder is properly sized or not. Square footage, connected load data plate information, and kilowatts of heat, etc are some of the types of information that would be needed. Really hard to say without that information. Do you at least have the panel schedule labeling for each of those breakers, and we can maybe hazard a guess as to whether it's definitely not okay?

[rmoewe]

The panel in not labled.

[pdoane]

Beyond your SOP. You need to do an actual load calc. as speedy and Marc have said. The sum of the breakers (amp potential) in a panel has nothing to due with the sizing of the main breaker. (i.e. the potential that ALL the circuits are on at one given time at their maximum load is not realistic as Speedy has also hinted to.) Manufacturers set their own panel ratings and can usually be found on their name plate. But I'm no expert and may be corrected as well.

[Marc D. Shunk]

Even if the feeder to that panel is undersized, that feeder is protected by a breaker in the main panel. As long as the feeder size jives with that feeder breaker size, no hazard exists. The breaker will trip if the feeder is ever overloaded. Might be a nuisance to someone in the future, if it were to happen, but certainly not a hazard. I don't know much about home inspection SOP, but I'd recommend that you concentrate you effort on making sure the feeder breaker matches the feeder gauge, and worry less about the actual connected load in the subpanel, unless you know how to do those calculations.

[Larry D. Kage]

Originally Posted by Marc D. Shunk

Even if the feeder to that panel is undersized, that feeder is protected by a breaker in the main panel. As long as the feeder size jives with that feeder breaker size, no hazard exists. The breaker will trip if the feeder is ever overloaded. Might be a nuisance to someone in the future, if it were to happen, but certainly not a hazard. I don't know much about home inspection SOP, but I'd recommend that you concentrate you effort on making sure the feeder breaker matches the feeder gauge, and worry less about the actual connected load in the subpanel, unless you know how to do those calculations.

Even if you do know how to do the calcs, it's is way beyond the SOP but looking for the hazard, as Marc explains it, is appropriate.

[Paul W. Abernathy]

Originally Posted by rmoewe

Can someone tell me what the MINIMUM size breaker is to supply a fairly large and full sub panel, (17 breakers, 2 of the 30 amp and the rest 15 and 20 amp breakers). I had one that the Main is not labeled, of course and can not tell what breaker the sub is being fed by. I do know that the supply wire to the sub is only a number 6, which is good for up to a 60 amp breaker. 60 amps does not seem to be big enough, to me.
Thanks, Rick

Speedy and Marc are very right here ....See the calculation is needed to determine the demand for this remote distribution panel and you simply have not given enough information for these gentlemen to assist you.

Yes. it is beyond scope and your efforts to care for your client is very noted and I totally understand but without the proper information it is hard to come up with the answers for you....we can hazard a guess if you can provide us with the dwelling square footage being served by this panel, the identified breakers within this panel ( if not labeled defer anyway and let the electrician handle it )...a # 6 to a remote distribution panel with lets see...(2) double poles and (13 ) single poles may appear as alot but without knowing exactly what is being supported by this remote distribution panel...it is a hard call.

As I believe peter stated.....you would be amazed the variety of calcs you can get using standard or optional methods and so on....so it is just not something you are gonna want to dabble in.....if you have other issues in this dwelling...defer the issues, make note of your concerns and let the electricians determine the rest.