Article 220 Calculating Loads for Service sizing

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ControlsRPS

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Automation Electrical Designer & Programmer
I am a member on other forums and before I chastise someone for this suggestion I want to see what other electricians think.

The problem: Existing single family home, All appliances are electric, forum member wants to add a 80A EV-Charger.
  • 3 quotes from local electricians all say service needs to be upgraded because service entry 200A doesn't have capacity to add 19.2KvA into the existing.
Lots of other members chiming in: Throw an Ammeter on there and see what you are actually using before you upsize your service.

The way I read Article 220, you can only use nameplate data, or standards to calculate load when sizing electrical service conductors. Does anyone know if using an Ammeter to check load is accepted as an acceptable method for service entry calculation?
 

ControlsRPS

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Yes, and I could be wrong, but the Ammeter needs to be in service recording peak usage for over 365days. Meaning you can't just slap an Ammeter on there today with all appliances on and determine the appropriate service required.
 

ControlsRPS

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read carefully what the exception actually says.
Back to the books... Thanks for the quick reply, investigating!


Reading...
The calculation of a feeder or service load for existing installations shall be permitted to use actual maximum demand to determine the existing load under all of the following conditions:
  1. The maximum demand data is available for a 1-year period.
    Exception: If the maximum demand data for a 1-year period is not available, the calculated load shall be permitted to be based on the maximum demand (the highest average kilowatts reached and maintained for a 15-minute interval) continuously recorded over a minimum 30-day period using a recording ammeter or power meter connected to the highest loaded phase of the feeder or service, based on the initial loading at the start of the recording. The recording shall reflect the maximum demand of the feeder or service by being taken when the building or space is occupied and shall include by measurement or calculation the larger of the heating or cooling equipment load, and other loads that may be periodic in nature due to seasonal or similar conditions.
  2. The maximum demand at 125 percent plus the new load does not exceed the ampacity of the feeder or rating of the service.
  3. The feeder has overcurrent protection in accordance with 240.4, and the service has overload protection in accordance with 230.90.
Exception: If the feeder or service has any renewable energy system (i.e., solar photovoltaic systems or wind electric systems) or employs any form of peak load shaving, this calculation method shall not be permitted.
Upon further reading, the exception cannot be applied if they have solar panels (of which I forgot to mention originally).


Thank you for this quick code review, so many exceptions and clauses! Stay safe.
 
Last edited:

jaggedben

Senior Member
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Northern California
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Solar and Energy Storage Installer
I've done 220.83 and .82 calcs on all-electric homes and come out below 150A, but not likely that will allow such a large car charger. 220.87 is probably your best bet. (If the heating appliances were gas I'd bet money the electricians were wrong.)
 

wwhitney

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Berkeley, CA
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Retired
I've done 220.83 and .82 calcs on all-electric homes and come out below 150A, but not likely that will allow such a large car charger.
With 220.82, wouldn't the 80A (continuous?) EVSE add only 32A (continuous?) to the result? For better or worse I don't see anything that say the EVSE shouldn't be included in 220.82(B)(3) calculation, which gets factored at 40%.

With respect to a PV system, if the feeder configuration includes a feeder that carries all the load but no PV, then 220.87 Exception could be used for that feeder, and the resulting load could be used for the service as well.

Cheers, Wayne
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
With 220.82, wouldn't the 80A (continuous?) EVSE add only 32A (continuous?) to the result? For better or worse I don't see anything that say the EVSE shouldn't be included in 220.82(B)(3) calculation, which gets factored at 40%.
Yes, that's what the code says. But I've run into a couple AHJs who don't buy it, they want the EVSE added to any 220 load calc at full nameplate. Which kinda makes sense because it really does charge continuously for hours, unlike, say, a dryer or oven which most likely cycles on and off on an internal thermostat. I'm kinda waiting for the other shoe to drop with respect to EVSEs and article 220.

With respect to a PV system, if the feeder configuration includes a feeder that carries all the load but no PV, then 220.87 Exception could be used for that feeder, and the resulting load could be used for the service as well.
I would say that by the standard of what you argue above, 220.87 could be used on a feeder or service that does have PV backfeeding it. Who knows, the PV backfeed might even be the peak demand. ;)
 

wwhitney

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Yes, that's what the code says. But I've run into a couple AHJs who don't buy it, they want the EVSE added to any 220 load calc at full nameplate.
I guess my attitude is that the whole 220.82 procedure is still a conservative method of estimating the actual load that would be determined by, say, 220.87. So it's unjustifiable to modify that for EVSEs when there's no code language to support such a modification.

Now if the starting point is the 220.87 measured load, then I see a strong argument for including a new EVSE at 100%.

I would say that by the standard of what you argue above, 220.87 could be used on a feeder or service that does have PV backfeeding it.
Sorry? I was referring to the Exception that was added to the end of 2020 NEC 220.87 (which I take to apply to the entire section, I think it should be a limitation specified at the beginning of the section, rather than an Exception). The one that was quoted: "Exception: If the feeder or service has any renewable energy system (i.e., solar photovoltaic systems or wind electric systems) or employs any form of peak load shaving, this calculation method shall not be permitted."

Cheers, Wayne
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I guess my attitude is that the whole 220.82 procedure is still a conservative method of estimating the actual load that would be determined by, say, 220.87. So it's unjustifiable to modify that for EVSEs when there's no code language to support such a modification.

Now if the starting point is the 220.87 measured load, then I see a strong argument for including a new EVSE at 100%.
I'm with you. I don't have strong feelings about how 220 should treat EVSE's except that I sort wish it would clarify the situation. It was not practical to try to argue with those AHJs.

That said, 220.87 is pretty clear that you'd have to add the EVSE at 100%, after adding 25% to the existing load.
Sorry? I was referring to the Exception that was added to the end of 2020 NEC 220.87 (which I take to apply to the entire section, I think it should be a limitation specified at the beginning of the section, rather than an Exception). The one that was quoted: "Exception: If the feeder or service has any renewable energy system (i.e., solar photovoltaic systems or wind electric systems) or employs any form of peak load shaving, this calculation method shall not be permitted."

Cheers, Wayne

Thanks for pointing out that new exception, I was not aware of it yet. I must have been looking at the 2017 book when I was reviewing 220.87 earlier. My comment would only apply under the earlier codes.

I do think the new exception needs to be modified to allow for cases where the data includes the renewable energy production such that the actual load can be accurately calculated.
 

wwhitney

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Berkeley, CA
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Retired
That said, 220.87 is pretty clear that you'd have to add the EVSE at 100%, after adding 25% to the existing load.
I'm not super familiar with 220, but I don't see how 220.87 requires the EVSE to be included at 100%. It just says "plus the new load" without specifying how to determine the new load. So I don't see why the new load couldn't be based on the 75% factor in 220.53 for the case of a new feeder with 4 or more new appliances. [Or perhaps fewer new appliances, as long as the dwelling unit as a whole has 4 or more appliances.]

Cheers, Wayne
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I'm not super familiar with 220, but I don't see how 220.87 requires the EVSE to be included at 100%. It just says "plus the new load" without specifying how to determine the new load. So I don't see why the new load couldn't be based on the 75% factor in 220.53 for the case of a new feeder with 4 or more new appliances. [Or perhaps fewer new appliances, as long as the dwelling unit as a whole has 4 or more appliances.]

Cheers, Wayne
Well, I was assuming only the EVSE is being added, as that's all that's mentioned in the OP. There are no demand factors in 220 for that. And in my experience it's the most common situation when adding an EVSE. Perhaps your scenario would be applicable to adding an ADU, if you can get that on the same meter (don't try it in Berkeley ;) ). Otherwise if you are adding 4 appliances then that's probably a remodel and I'd say it starts to get tricky as to whether the installation is 'existing', or the advantage of saying so disappears. (Like when the 'remodel' is actually tearing down and rebuilding 90% of the home, but they manage to keep the same electrical service. I used 220.82 for that one.)
 

wwhitney

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Berkeley, CA
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Retired
That raises the question posed in the last bracketed comment in my post: if there are 4 existing appliances that meet the 220.53 requirement, and you add a single new appliance, does it get to use the 75% factor when calculating the "new load"? Seems plausible to me. And 75% is alot more than 40%.

Cheers, Wayne
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
That raises the question posed in the last bracketed comment in my post: if there are 4 existing appliances that meet the 220.53 requirement, and you add a single new appliance, does it get to use the 75% factor when calculating the "new load"? Seems plausible to me. And 75% is alot more than 40%.

Cheers, Wayne
No. The 3 other appliances are included in the existing load. Given that the existing demand data will likely, in effect, be giving you a demand factor allowance, then it would be double-counting to take another one. (Or, the case where the existing demand data shows the full load of the 3 appliances without a demand factor, it might be more to your advantage to use another code section.)

At a certain point it's just not doing due diligence to stretch the language of the code to your advantage just because you can make a semantic argument.
 

wwhitney

Senior Member
Location
Berkeley, CA
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Retired
No. The 3 other appliances are included in the existing load. Given that the existing demand data will likely, in effect, be giving you a demand factor allowance, then it would be double-counting to take another one.
But multiplication is distributive over addition, so how is it double counting?

I.e. the two options I propose, for existing loads A, B and C, and new load D, are:
(a) calculate 0.75 A + 0.75 B + 0.75 C + 0.75 D
(b) instead of calculating 0.75A, 0.75B, and 0.75C, those are part of the measurement. Now add 0.75D.

In any event, I think we agree on what would be allowed by the current wording if adding 4 EVSEs, and the resulting potential issue as Article 220 does not address the unusual load characteristics of an EVSE. Whether that same issue exists with adding just 1 EVSE, I don't know.

[But I do know that if your interpretation is adopted by an AHJ, you can just put 3 incidental 100 W appliance loads on the new feeder, and now you get the potentially problematic 0.75 factor. So in that sense it doesn't matter.]

Cheers, Wayne
 
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