EV Charger Calculation

[Dennis Alwon]

In the 2023 we are told that we are to use 7200 watts or the nameplate whichever is larger. 220.57

In 220.53 we are told that EV Chargers are NOT included in the appliance load.

For standard calculation we use 100% but what about optional calc. Do we use it at 100% or does it get the demand factor as many of the other loads get. In other words does it get put with all other loads and get the first 8k at 100% and the rest at 40% OR gets calculated after that at 100%. My guess is we get to take the demand factor on it since we are not told otherwise.

220.57 Electric Vehicle Supply Equipment (EVSE) Load
The EVSE load shall be calculated at either 7200 watts (volt-amperes) or the nameplate rating of the equipment, whichever is larger.

220.53 Appliance Load — Dwelling Unit(s).
Applying a demand factor of 75 percent to the nameplate rating load of four or more appliances rated 1⁄4 hp or greater, or 500 watts or greater, that are fastened in place, and that are served by the same feeder or service in a one-family, two-family, or multifamily dwelling shall be permitted. This demand factor shall not apply to the following:

• Household electric cooking equipment that is fastened in place
• Clothes dryers
• Space heating equipment
• Air-conditioning equipment
• Electric vehicle supply equipment (EVSE)

 

[wwhitney]

My guess is we get to take the demand factor on it since we are not told otherwise.

Indeed. Also, 220.57 does not apply, as it is in Part III of Article 220. We use the nameplate rating of the EVSE, without any 7200W minimum.

This changed in the 2026 NEC First Draft. Article 220 moved to Article 120, and there is a new section 120.82(D) which says: "The total load of an EVSE shall be calculated at 100 percent in accordance with 120.57." Although 120.57 has also changed, so the 7200W minimum does not always apply.

Cheers, Wayne

 

[Jaybone812]

In the 2023 we are told that we are to use 7200 watts or the nameplate whichever is larger. 220.57

In 220.53 we are told that EV Chargers are NOT included in the appliance load.

For standard calculation we use 100% but what about optional calc. Do we use it at 100% or does it get the demand factor as many of the other loads get. In other words does it get put with all other loads and get the first 10k at 100% and the rest at 40% OR gets calculated after that at 100%. My guess is we get to take the demand factor on it since we are not told otherwise.

I’m in agreement with you and that’s what I’ve done with the evse load when using the optional method . 100% of the nameplate gets factored into all other loads before applying the demand factor . But I’ve also wondered if i was correct in doing so more than once lol


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[wwhitney]

that’s what I’ve done with the evse load when using the optional method . 100% of the nameplate gets factored into all other loads before applying the demand factor .

That's a conservative choice but not required by the language in 2023 NEC 220.82. You can apply the 40% demand factor to the EVSE, although arguably that could be non-conservative in extreme cases. So some judgement is appropriate.

As I mentioned, this is currently planned to change in the 2026 NEC.

Cheers, Wayne

 

[Jaybone812]

That's a conservative choice but not required by the language in 2023 NEC 220.82. You can apply the 40% demand factor to the EVSE, although arguably that could be non-conservative in extreme cases. So some judgement is appropriate.

As I mentioned, this is currently planned to change in the 2026 NEC.

Cheers, Wayne

Exactly that’s what i said sorry if I was unclear . I add the evse kw rating from the nameplate to the loads before applying the allowed demands in the optional method so it’s nameplate rating is included in all other loads then the 40% demand factor is applied

 

[nizak]

That's a conservative choice but not required by the language in 2023 NEC 220.82. You can apply the 40% demand factor to the EVSE, although arguably that could be non-conservative in extreme cases. So some judgement is appropriate.

As I mentioned, this is currently planned to change in the 2026 NEC.

Cheers, Wayne

I would think that applying a 40% demand factor to say an 80 amp EVSE wouldn’t be prudent.

I recently installed a 100A ( 80A charge) for a homeowner.

In speaking with him a few weeks later he’s telling
me that with his driving habits it’s not uncommon to have 8 hours or more of continuous charging.

That’s alot of amps for a lot of time.

 

[Jaybone812]

I would think that applying a 40% demand factor to say an 80 amp EVSE wouldn’t be prudent.

I recently installed a 100A ( 80A charge) for a homeowner.

In speaking with him a few weeks later he’s telling
me that with his driving habits it’s not uncommon to have 8 hours or more of continuous charging.

That’s alot of amps for a lot of tim

I install at Least 3-5 level 2 charging stations every week , it’s a decent portion of our work being certified Tesla installers. And i can say that 6-8 hour charging times is not uncommon, but what’s very common is the time of day they charge . The most common time to charge is through the night and allot of times that evse is pretty much the only load on the service when charging so using the demand in the optional method is never a problem

 

[Dennis Alwon]

Indeed. Also, 220.57 does not apply, as it is in Part III of Article 220. We use the nameplate rating of the EVSE, without any 7200W minimum.

This changed in the 2026 NEC First Draft. Article 220 moved to Article 120, and there is a new section 120.82(D) which says: "The total load of an EVSE shall be calculated at 100 percent in accordance with 120.57." Although 120.57 has also changed, so the 7200W minimum does not always apply.

Cheers, Wayne

I realize 220.53 and .57 don't apply to optional. My point was the optional calc doesn't directly tell us what to do but since it doesn't state 100% as it does for air conditioning then I assumed it should be in with the rest of the calculation at 40%

 

[Jaybone812]

I realize 220.53 and .57 don't apply to optional. My point was the optional calc doesn't directly tell us what to do but since it doesn't state 100% as it does for air conditioning then I assumed it should be in with the rest of the calculation at 40%

I think he misunderstood what we said and was under the impression we thought the evse was factored in at 100% after the demand. Like a hvac load but , but it obviously doesn’t
the total evse nameplate rating is added to all other loads before the optional method demands factors are applied,


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[Jaybone812]

I realize 220.53 and .57 don't apply to optional. My point was the optional calc doesn't directly tell us what to do but since it doesn't state 100% as it does for air conditioning then I assumed it should be in with the rest of the calculation at 40%

the only real difference i see between the standard and optional method when adding in the evse to the calculation is the optional method doesn’t allow you the option to use the 7200 watt value in 220.57 , the total nameplate must be included in the optional calculation


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[nizak]

I would think that applying a 40% demand factor to say an 80 amp EVSE wouldn’t be prudent.

I recently installed a 100A ( 80A charge) for a homeowner.

In speaking with him a few weeks later he’s telling
me that with his driving habits it’s not uncommon to have 8 hours or more of continuous charging.

That’s alot of amps for a lot of time.

I install at Least 3-5 level 2 charging stations every week , it’s a decent portion of our work being certified Tesla installers. And i can say that 6-8 hour charging times is not uncommon, but what’s very common is the time of day they charge . The most common time to charge is through the night and allot of times that evse is pretty much the only load on the service when charging so using the demand in the optional method is never a problem

Is a 100A level 2 charging station pretty much the largest you install for residential?


As far as charging at night you make a valid point.
Even with AC running at night the higher Seer ratings have taken away a lot of the heavy loads we used to see with HVAC

 

[Jaybone812]

Is a 100A level 2 charging station pretty much the largest you install for residential?


As far as charging at night you make a valid point.
Even with AC running at night the higher Seer ratings have taken away a lot of the heavy loads we used to see with HVAC

For residential yes. Typically 60 amp level 2 hardwired charging stations is the norm but but 100 amp stations come up periodically. I wired a 80 amp (100 amp circuit ) prime com tech charging station last week . Only difference during the install is there’s an extra step over 60 amps because of the need for tge disconnect

 

[retirede]

Is a 100A level 2 charging station pretty much the largest you install for residential?

I believe 80A (100A circuit) is the maximum allowed per the J1772 standard.

 

[Elect117]

I do not believe a DF should be applied to the EVSE circuit for more than just engineering concerns but I also believe that it is not the intent of the code. It is not a load that would, under normal conditions, be operating at less than nameplate or likely to be less than the assumed load. Given you can reduce it to the EVSE's nameplate or set point. That makes it not similar to that of lighting, receptacles, or simple appliances. To which the DFs are normally used.

EVSEs, while mainly used for charging cars, would also need to assume the backfeed application in some regard. You wouldn't apply a demand factor to an interconnection. You could, however, take into account PCS or EMS (Power Control Systems / Energy Management Systems) using the standard method. I don't know if you could use PCS / EMS with the optional method since it is located in part 3. But I digress.

I find that 220.40's language, while located in Part 3, covers the optional method as well with regard to "The calculated load of a feeder or service shall not be less than the sum of the loads on the branch circuits supplied, as determined by Part II of this article, after any applicable demand factors permitted or required by Part III, IV, V, VI, or VII have been applied." Since the optional method does not consider EVSE in it's method, it is not applicable and therefore not permitted or required.

At a minimum, you should never had a EV charger circuit that is larger than your calculated load after demand factors.

 

[wwhitney]

I do not believe a DF should be applied to the EVSE circuit for more than just engineering concerns but I also believe that it is not the intent of the code.

Agreed that the correct way to write an electrical code would require a 100% demand factor for an EVSE when calculating a group of loads including only one EVSE. And that is what the 2026 NEC does. But that is not what the wording of the 2023 NEC and earlier does with respect to the optional calculation.

I find that 220.40's language, while located in Part 3, covers the optional method as well with regard to "The calculated load of a feeder or service shall not be less than the sum of the loads on the branch circuits supplied, as determined by Part II of this article, after any applicable demand factors permitted or required by Part III, IV, V, VI, or VII have been applied." Since the optional method does not consider EVSE in it's method, it is not applicable and therefore not permitted or required.

Two problems with that argument: 220.82(A) explicitly says "instead of the method specified in Part III of this article." At face value, that means ignore 220.40, since it is Part 3. Under the theory that 220.82 can't do that unless 220.40 allows it to, 220.40's language still permits 220.82 to apply a 40% demand factor, so I see no conflict.

Secondly, 220.82(A) says "The calculated load shall be the result of adding the loads from 220.82(B) and (C)." It doesn't say "at least" or "plus 100% of any loads not listed in (B) and (C)". So the default for a load not listed in (B) and (C) is to omit it from the calculation, not to include it at 100%.

Fortunately, this disagreement about the meaning of the 2023 and earlier NECs will soon be rendered moot by the 2026 NEC, so I see no particular reason to further pursue this argument.

Cheers, Wayne

 

[Elect117]

Fortunately, this disagreement about the meaning of the 2023 and earlier NECs will soon be rendered moot by the 2026 NEC, so I see no particular reason to further pursue this argument.

Cheers, Wayne

I know, but we do it every time. lol