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EV chargers & residential load calcs

Merry Christmas
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A

aekrogh

Member
Location
Southern California
Occupation
Plans Examiner / Building Inspector
When doing residential load calculations are EV chargers considered at 100% load or are they part of the general/remaining loads and are reduced to 40% as per 2019 CEC/ 2017 NEC 220.83? This specific residence is adding two tesla 9,600va wall chargers. The house is 2800 sqft so the first 8000va @ 100% is used with the 3va per sqft from the beginning. Any specific code sections would be very helpful. Thanks.
 
M

MyCleveland

Senior Member
Location
Cleveland, Ohio
aekrogh
My take from 2017 is you are not allowed access to the 40% discount. There is another thread recently discussing this issue so I know others will disagree.

The argument that the EVCS is just another appliance I do not believe it holds, or at least until CMPs clear this up in writing.

The "appliance" definition that includes AC I believe is applicable yes just like ranges, dryers, etc. ; however, in 220.82 B where it lists items that can be reduced by 40% it specifically calls out ranges...dryers...and water heaters so these larger items cannot be assumed to fall under 220.82B.3a.

Just my take...
 
W

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
So what part of 220.82 requires a 100% factor rather than a 40% factor? It's only got part (B) General Loads and part (C) HVAC Load, and an EVSE certainly isn't an HVAC load.

My understanding is that 40% is allowed, but perhaps shouldn't be, although Article 220 is so conservative that it usually doesn't matter.

Cheers, Wayne
 
M

MyCleveland

Senior Member
Location
Cleveland, Ohio
wwhitney said:
So what part of 220.82 requires a 100% factor rather than a 40% factor? It's only got part (B) General Loads and part (C) HVAC Load, and an EVSE certainly isn't an HVAC load.

My understanding is that 40% is allowed, but perhaps shouldn't be, although Article 220 is so conservative that it usually doesn't matter.

Cheers, Wayne
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What part of 220.82 requires 100%…none specifically, but what part allows the 40% discount?

I am not saying you are incorrect. I was just trying to state why I thought the 40% could not be used.

If you look over 220.82B 3 a,b,c,&d.
Note that the most typical large load appliances are each called out by name in b,c,&d.
If they were considered a simple appliance could we not just delete b,c,&d as they would fall under a.

I am just extrapolating the fact that specific large load appliances are itemized by name in b,c, &d, and because EV charger is NOT listed you are not entitled to usethe 40% discount.
 
W

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
If there were a (D) Everything else at 100%, I would probably agree with you. As there isn't, it's either don't count it, 40% (B), or 100% (C). Since it's not HVAC equipment, it's 40% (B).

Cheers, Wayne
 
M

MyCleveland

Senior Member
Location
Cleveland, Ohio
wwhitney said:
If there were a (D) Everything else at 100%, I would probably agree with you. As there isn't, it's either don't count it, 40% (B), or 100% (C). Since it's not HVAC equipment, it's 40% (B).

Cheers, Wayne
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Cannot argue against you on this. I struggle with 2 and maybe even a 3rd being added in at 40%. Do you know if they have addressed this possibly in the 2023?
 
Dennis Alwon

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Our state engineer said to figure it at 100% but that is his opinion and certainly a safe one at that.

I have heard some of these units read how much the service is using and adjusts as it sees fit. Must be some monitor added in the panel to do this
 
T

topgone

Senior Member
Dennis Alwon said:
Our state engineer said to figure it at 100% but that is his opinion and certainly a safe one at that.

I have heard some of these units read how much the service is using and adjusts as it sees fit. Must be some monitor added in the panel to do this
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And that falls under "engineering supervision". If the PE did his homework and says it is so, anything going wrong with his design in on him!
 
A

aekrogh

Member
Location
Southern California
Occupation
Plans Examiner / Building Inspector
My concern is that the system is so large it requires the derating of the main service breaker to 175 amps. With the two EV circuits at 40% calculated load and the rest of the loads it shows the minimum service size for the home at 172.79 amps so 175 works. if you figure the EV @ 100% then it puts the required service size at 218 amps which is allowable on the 225 amp service and buss rating... I for see the main service breaker being tripped and causing nuisance issues with a derated main and the loads being purposed. I found what I was looking for the justify the 100% load application. . Per 2019 CEC based on the 2017 NEC- code for EV chargers- 625.42 Rating. The equipment shall have sufficient rating to supply the load served. Electric vehicle charging loads shall be considered to be continuous loads for the purposes of this article. Where an automatic load management system is used, the maximum equipment load on a service and feeder shall be the maximum load permitted by the automatic load management system.
 
W

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Continuous vs non-continuous loads is an issue unrelated to 40% vs 100% in 220.82. Note that the only place in Article 220 the word "continuous" is used as in continuous load is in 220.82(C)(6) with respect to heating equipment.

If the house has (2) 40A (continuous) EVSEs on 50A circuits, then the 40% vs 100% computation would be a difference of 60% * 80A = 48A, but your numbers differ by 45A. Regardless, 173A is the correct computation under 220.82. Nothing there calls for a 100% factor for EVSEs. If you feel it should, then a proposal to change 220.83 for the 2026 NEC is in order.

You are correct that if two EVs are charging at the full 40A rate, that will be an actual 80A load on the service, leaving only 120A of headroom for the other 141A of calculated load. [Or 95A of headroom if the service OCPD is being reduced to 175A for, say, a PV or ESS installation.] But the same is true for any other load that gets a 40% factor in 220.82. EVs typically charge overnight, so concomitant loads will typically be less than normal.

Cheers, Wayne
 
gadfly56

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
wwhitney said:
Continuous vs non-continuous loads is an issue unrelated to 40% vs 100% in 220.82. Note that the only place in Article 220 the word "continuous" is used as in continuous load is in 220.82(C)(6) with respect to heating equipment.

If the house has (2) 40A (continuous) EVSEs on 50A circuits, then the 40% vs 100% computation would be a difference of 60% * 80A = 48A, but your numbers differ by 45A. Regardless, 173A is the correct computation under 220.82. Nothing there calls for a 100% factor for EVSEs. If you feel it should, then a proposal to change 220.83 for the 2026 NEC is in order.

You are correct that if two EVs are charging at the full 40A rate, that will be an actual 80A load on the service, leaving only 120A of headroom for the other 141A of calculated load. [Or 95A of headroom if the service OCPD is being reduced to 175A for, say, a PV or ESS installation.] But the same is true for any other load that gets a 40% factor in 220.82. EVs typically charge overnight, so concomitant loads will typically be less than normal.

Cheers, Wayne
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Hmmmm, I wonder if there are folks out there that start the Thanksgiving or Christmas turkey at 11:00 at night? :unsure: Oven on a timer; could easily run for 4 hours.
 
gadfly56

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
retirede said:
But still, it only takes about 5 hours to cook an average size turkey!
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Yes, but there are many other dishes requiring access to the oven, including the biscuits. She's not getting up at o'dark thirty to start the turkey.
 
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