Calculations load help please. New to this.

S

sparkygbninja

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Location
Ca
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Journeyman electrician c10 contractor
Hello, hopefully I can make sense. I'm doing an ev charger level 2 install for a client. I. Asking for help on the calculation loads fill out sheet.

Do I need to see every spec of every appliance or a/c, etc?

Do I need to get the amps from what each breaker is pulling while on?

Or do I just go in the nec code book to the load calculations and do it from there?

Do I need to go back to the house for anything besides install?

Any info helps please. I'm new to this part, if i keep asking the city guy helping but he's not specific on anything and it's confusing.

He said the planner wants me to add the amps to the breakers. Don't know if that's separate or use it as a help for the load calculations.
 
I am going through this same calculation for adding two EVSE to an office building. This is new to me as well, and I will write how I am approaching it and ask for feedback from others with more experience:
Site has 208/120 3-phase 200A service. Occupancy is Office, which looks like I can use square footage (4600) to calc general lighting loads, and then for general receptacle loads, I use the higher of either 1VA/sq ft or 180VA per receptacle. Then I add specific loads for HVAC, Range, H20 Tank, and DW/Disp.

Calculations:
Gen Lighting - 4600 x 1.3 VA = 5980 VA
Gen Recept (SF method) - 4600 x 1 VA = 4600 VA
Gen Recept (Count Recept method) - 75 x 180 VA = 13500 VA (I estimated 3 receptacles per branch breaker) *This is higher than SF method
Specific Loads:
HVAC #1 - 20160 VA (I estimated this from the 70A breaker)
HVAC #2 - 11520 VA (I estimated this from the 40A breaker)
H20 Tank - 3500 VA (3500W on nameplate)
Range - 6656 VA (I estimated by 40A breaker, 208V)
DW/Disp - 1920 (estimated by 20A breaker, 120V)

Total = 5980 + 13500 + 20160 + 11520 + 3500 + 6656 +1920 = 63,326 VA

Phase Current = 63,326 VA / (120*3) = 175.9 A

In my case, this is bad, since I am trying to add two EVSE at 208V x 48A, or additional 19,968 VA. That would be 231 A total on the 200A service.

I am going to get more details on the loads I estimated to see if it can still work. Appreciate any feedback if I am missing or miscalculated anything that can help. Thanks.
 
Last edited:
solarken said:
I am going through this same calculation for adding two EVSE to an office building. This is new to me as well, and I will write how I am approaching it and ask for feedback from others with more experience:
Site has 208/120 3-phase 200A service. Occupancy is Office, which looks like I can use square footage (4600) to calc general lighting loads, and then for general receptacle loads, I use the higher of either 1VA/sq ft or 180VA per receptacle. Then I add specific loads for HVAC, Range, H20 Tank, and DW/Disp.

Calculations:
Gen Lighting - 4600 x 1.3 VA = 5980 VA
Gen Recept (SF method) - 4600 x 1 VA = 4600 VA
Gen Recept (Count Recept method) - 75 x 180 VA = 13500 VA (I estimated 3 receptacles per branch breaker) *This is higher than SF method
Specific Loads:
HVAC #1 - 20160 VA (I estimated this from the 70A breaker)
HVAC #2 - 11520 VA (I estimated this from the 40A breaker)
H20 Tank - 3500 VA (3500W on nameplate)
Range - 6656 VA (I estimated by 40A breaker, 208V)
DW/Disp - 1920 (estimated by 20A breaker, 120V)

Total = 5980 + 13500 + 20160 + 11520 + 3500 + 6656 +1920 = 63,326 VA

Phase Current = 63,326 VA / (120*3) = 175.9 A

In my case, this is bad, since I am trying to add two EVSE at 208V x 48A, or additional 19,968 VA. That would be 231 A total on the 200A service.

I am going to get more details on the loads I estimated to see if it can still work. Appreciate any feedback if I am missing or miscalculated anything that can help. Thanks.
Click to expand...
IMO your math looks right. You may be able to shave a little off your receptacle load but it wouldn’t be much at all (220.47).
Also your EV will be continuous duty so your calculation for them should be increased 25% unfortunately.

The only thing I would think you MAY be able to do is to do a load shedding where your ac’s (or the bigger one) doesn’t run along with some of your other loads plus your EV’s can’t operate at the same time.
Otherwise you’ll need more power
 
PaulEd said:
IMO your math looks right. You may be able to shave a little off your receptacle load but it wouldn’t be much at all (220.47).
Also your EV will be continuous duty so your calculation for them should be increased 25% unfortunately.

The only thing I would think you MAY be able to do is to do a load shedding where your ac’s (or the bigger one) doesn’t run along with some of your other loads plus your EV’s can’t operate at the same time.
Otherwise you’ll need more power
Click to expand...
Thanks for response. For EVSE, I read 220.57 to use either 7200 watts or the nameplate rating, whichever is larger, with no x 1.25 multiplier.
 
sparkygbninja said:
Hello, hopefully I can make sense. I'm doing an ev charger level 2 install for a client. I. Asking for help on the calculation loads fill out sheet.

Do I need to see every spec of every appliance or a/c, etc?

Do I need to get the amps from what each breaker is pulling while on?

Or do I just go in the nec code book to the load calculations and do it from there?

Do I need to go back to the house for anything besides install?

Any info helps please. I'm new to this part, if i keep asking the city guy helping but he's not specific on anything and it's confusing.

He said the planner wants me to add the amps to the breakers. Don't know if that's separate or use it as a help for the load calculations.
Click to expand...
2023 NEC TX
Section 220.57 Electric Vehicle Supply Equipment(EVSE) Load Calculate either 7200VA or nameplate rating whichever is larger.

That's all you need to get started.

But there's more.
Much more that's found in Article 625. Such as GFCI, 625 52 Ventilation, (A) Ventilation 625(A) or (B) and T. 625.52(B) (1)(2).

So, read that article for more info.

I don't know about going back to the house for anything besides ........getting paid!

The city guy-planner won't tell you how to do your job.

If you're new, then you need to get a licensed electrician and leave it alone.

TX+MASTER#4544
 
solarken said:
Thanks for response. For EVSE, I read 220.57 to use either 7200 watts or the nameplate rating, whichever is larger, with no x 1.25 multiplier.
Click to expand...
2023 NEC TX

625.40,41 OCPD at 125 %

625.42 Rating.............considered to be continuous loads

TX+MASTER#4544
 
PaulEd said:
But doesn’t NEC 625.42 require an additional 25% for your load calculation? Despite 7200va?
Click to expand...
2023 NEC TX
Yes. Despite.

Use 7200 watts or VA (or nameplate whichever's larger) 7200 VA x 1.25 = 9,000 VA 9,000VA / 240 volts = 37.5 or 38 amps round up to a 40-amp OCPD.

Size conductors using the 75-degree column T.310.16 size 8 AWG CU for THHN

If it's romex use the 60-degree column. T.310.16 size 8 AWG NM CU

TX+MASTER#4544
 
PaulEd said:
But doesn’t NEC 625.42 require an additional 25% for your load calculation? Despite 7200va?
Click to expand...
No.
TX+ MASTER#4544 said:
2023 NEC TX
Yes. Despite.

Use 7200 watts or VA (or nameplate whichever's larger) 7200 VA x 1.25 = 9,000 VA 9,000VA / 240 volts = 37.5 or 38 amps round up to a 40-amp OCPD.

Size conductors using the 75-degree column T.310.16 size 8 AWG CU for THHN

If it's romex use the 60-degree column. T.310.16 size 8 AWG NM CU

TX+MASTER#4544
Click to expand...
That's not a load calculation. That's a branch circuit sizing calculation.
 
david luchini said:
625.42 says ....considered to be continuous loads for the purposes of this article
Click to expand...
True. But most 16A-40A EVSEs will meet the definition of continuous load independently. I.e. it is expected that an EV that can utilize the maximum rating of the EVSE will be plugged in and will charge for over 3 hours, drawing the full rated current of the EVSE.

Now if you install an 80A EVSE, there aren't many cars out there with onboard chargers capable of accepting 80A AC, so you might be able to argue that such an EVSE is not a continuous load except as required by Article 625. Although if you buy an EV that can use that EVSE at 80A, then charging for the full 80A for 3 hours would be expected. So still not clear to me.

[Using the word "load" here loosely, the EVSE is not utilization equipment, the EV is.]

Cheers, Wayne
 
david luchini said:
No.

That's not a load calculation. That's a branch circuit sizing calculation.
Click to expand...
2023 NEC TX
Ok, so we can call it adding some numbers together to arrive at a sum of the numbers.
NFPA should be notified that it is not correct to label Article 220 Branch-Circuit, Feeder, and Service Load Calculations.
Maybe we should call it.... installing requirements for electrical installations.

Dennis, submit this to NFPA for an amendment.

TX+MASTER#4544
 
The OP is presumably asking about adding a EVSE to a single family dwelling, and in that case the service entrance conductors can be sized per 310.12(A) - 230.79 as opposed to 230.42(A).
 
The following will likely appear in the 2026 code:
120.5(E) Percent Multiplier.
Load calculations shall not require continuous loads to be calculated at 125 percent.
Informational Note: A 125-percent multiplier could be required for reasons other than continuous load. Continuous loads impact the sizing of the conductor and overcurrent device but might not influence the load.

The substantiation was:

For the 1999 NEC Code Cycle the TCC Task Group on the Usability of the NEC, submitted a proposal with the following substantiation: “The proposal serves to make Article 220 a true calculations article and relocate any other requirements (such as conductor or overcurrent device sizing) to the appropriate parts of Articles 210” (refer to NEC-ROP-1998, Proposal 2-5). Load calculations in Article 220 are not intended to require a 125- percent multiplier simply due to the fact that the load is considered continuous. However, there are Sections in Article 220 that do require a 125 percent multiplier. To improve clarity, a new sub-section is added to Section 220.5 that addresses this issue. Also included is an Informational Note that explains that being a continuous load impacts the sizing of the conductor and overcurrent device, but not necessarily the computation of the load when performing a load calculation.
Click to expand...
Note that Article 220 in the previous codes becomes Article 120 in the 2026 code.
 
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