Max loads per panel rating

[jayrob]

We're running in to a plan checker that is giving us grief if there combined loads add up to more than the panel rating. (he actually says the loads can't be more than 120% of the panel rating)

We understand the 120 percent rule and how it applies to the solar backfeed plus disconnect breaker etc.

Is there any information I can share with this guy to help him understand about the loads?

Thanks in advance!

 

[jaggedben]

Best advice I can give is to get them on the phone and recite 705.12(D)(2)(3)(b) over and over again like a broken record. Assuming that's the section you are qualifying this under. Or try to go to the supervisor, since that's obviously a pretty green plan checker.

 

[don_resqcapt19]

The actual loads are not permitted to exceed the rating of the panel. Is he looking at the load calculation, or just summing the breaker ratings?

 

[electrofelon]

We're running in to a plan checker that is giving us grief if there combined loads add up to more than the panel rating. (he actually says the loads can't be more than 120% of the panel rating)

We understand the 120 percent rule and how it applies to the solar backfeed plus disconnect breaker etc.

Is there any information I can share with this guy to help him understand about the loads?

Thanks in advance!

Perhaps you could explain that prior to 2014 (IIRC, maybe 2011, the 120% rule was king, but there are multiple methods now to assure busbars are not overloaded.

 

[jayrob]

The actual loads are not permitted to exceed the rating of the panel. Is he looking at the load calculation, or just summing the breaker ratings?

Yes he's just summing the breakers (loads) and if they add up to more than 120 percent of the panel rating, he wants load calcs or add a sub panel and relocate breakers. (which seems ridiculous because we still have to feed the sub with enough amps to cover the loads being relocated)

 

[jayrob]

Best advice I can give is to get them on the phone and recite 705.12(D)(2)(3)(b) over and over again like a broken record. Assuming that's the section you are qualifying this under. Or try to go to the supervisor, since that's obviously a pretty green plan checker.

Looks like he's reading 705.12(D) (2) (c) where it talks about the warning signs. It says something about the sum of all load and supply cannot exceed the rating of the buss bar.

 

[jaggedben]

The actual loads are not permitted to exceed the rating of the panel. Is he looking at the load calculation, or just summing the breaker ratings?

For what it's worth, I've never been asked to provide a load calculation for existing loads just because we were adding solar to a panelboard whose rating and OCPD were clear (i.e. no missing labels) and not being changed by us.

I guess the reasoning is basically:
- solar is not a load
- if the existing main breaker is not tripping, it's sufficient for the load; if it weren't the customer would be addressing that
- existing stuff is grandfathered if not obviously out of compliance

Looks like he's reading 705.12(D) (2) (c) where it talks about the warning signs. It says something about the sum of all load and supply cannot exceed the rating of the buss bar.

Point out that the preceding language says "One of the following methods shall be used to determine the ratings...". Be clear which one you are using. If you are using (b) then see comments above. If you're using (c) then 120 percent does not figure.

 

[don_resqcapt19]

Yes he's just summing the breakers (loads) and if they add up to more than 120 percent of the panel rating, he wants load calcs or add a sub panel and relocate breakers. (which seems ridiculous because we still have to feed the sub with enough amps to cover the loads being relocated)

I have never seen a panel where the sum of the breaker ratings was not far in excess of the panel bus rating. The breaker ratings have nothing to do with the actual loads. As far as the 120% rule, that also has nothing to do with the breakers in the panel, other than the one that provides the overcurrent protection for the panel itself and the one from the solar supply.

 

[don_resqcapt19]

For what it's worth, I've never been asked to provide a load calculation for existing loads just because we were adding solar to a panelboard whose rating and OCPD were clear (i.e. no missing labels) and not being changed by us.

I guess the reasoning is basically:
- solar is not a load
- if the existing main breaker is not tripping, it's sufficient for the load; if it weren't the customer would be addressing that
- existing stuff is grandfathered if not obviously out of compliance



Point out that the preceding language says "One of the following methods shall be used to determine the ratings...". Be clear which one you are using. If you are using (b) then see comments above. If you're using (c) then 120 percent does not figure.

I agree that the solar is not a load and there is not need to do a panel load calculation to add solar. That should have been done at the time the panel was installed. You are correct of the actual loads are too much for the panel, the supply side OCPD should trip.