basic load calcs

[Carultch]

I was doing a EVSE install for a local city, and the plan check department insisted I had to count the solar as a load for the load calculation. I wonder how many unnecessary panel upgrades they've helped sell by requiring that... :roll:

Do they understand that solar is a source, rather than a load?

Except for the tiny standby loads, solar is never going to make your service draw a significant increase in current beyond what the loads draw with the solar off.

We already have a rule limiting the solar capacity to not exceed the rating of the service, in the event that there is full sun and zero loads. Solar affects the conditions in the hardware at the point of interconnection, but it doesn't change your service size.

 

[Carultch]

But your on site load offsets this, is there anything in art 220 that tells us how to calculate for on site production that backfeeds the grid? I could be wrong but I don't think so. Art 220 is primarily for on site loads. Those on site production loads are covered in 690, 694, or whatever article applies to the type of production.

It's an either/or calculation. Either the loads without the solar drive the sizing of the service, or the solar without the loads drives the sizing of the service.


You can't subtract one from the other to take credit for a reduction in amps. Because consider the scenario where either of the above equals zero, for one reason or another.

 

[kwired]

Do they understand that solar is a source, rather than a load?

Except for the tiny standby loads, solar is never going to make your service draw a significant increase in current beyond what the loads draw with the solar off.

We already have a rule limiting the solar capacity to not exceed the rating of the service, in the event that there is full sun and zero loads. Solar affects the conditions in the hardware at the point of interconnection, but it doesn't change your service size.

It's an either/or calculation. Either the loads without the solar drive the sizing of the service, or the solar without the loads drives the sizing of the service.


You can't subtract one from the other to take credit for a reduction in amps. Because consider the scenario where either of the above equals zero, for one reason or another.

I think we are on same page here, starting with the concept that solar is a source and not a load.

Sure it's effects need consideration when selecting conductors and equipment that carry the current it produces, then can be complicated even more by loads being served, but when doing a load calculation on a building you look at the building loads. If you are then going to have on site produced power mixed in with utility supply you have to consider any effects depending on how it gets tied in.

If you have more solar power then you have load in the building - then you must be able to at least carry the current with supply conductors and equipment that will be feeding back to the utility, if your solar power is less then the maximum demand of your loads then your supply conductors and equipment need to at least be able to handle the load demand.

You may have either/or or you may have something in the middle, but with either/or approach you have both extremes covered.