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Calculations load help please. New to this.

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sparkygbninja

Member
Location
Ca
Occupation
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.
 
S

solarken

NABCEP PVIP
Location
Hudson, OH, USA
Occupation
Solar Design and Installation Professional
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:
P

PaulEd

Member
Location
United States
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
 
S

solarken

NABCEP PVIP
Location
Hudson, OH, USA
Occupation
Solar Design and Installation Professional
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.
 
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