How to calculate panel load

L

Latenighthunter01

Member
Location
United States
Occupation
Assistant Engineer
Good day, I am creating a panel schedule and need to put how much W each circuit is going to carry. My question is how do I calculate for each lighting and Receptacle for example the living room has 10 lights do I calculate it by using the square footage and multiplying by 3VA or do I use the fixture wattage. And for receptacle do I need to do it as 180 for each recaptacle?
 
Latenighthunter01 said:
My question is how do I calculate for each lighting and Receptacle for example the living room has 10 lights do I calculate it by using the square footage and multiplying by 3VA
Click to expand...
If your going by the NEC branch circuit loads are calculated per 210.11, which points you to 220.10 in the 2023 NEC, which then points you to 220.41 and then you get your answer yes you use 3VA per sq ft if its a one-family, two-family or multifamily dwelling and the lighting and receptacles are described in items 1-3.
 
tortuga said:
If your going by the NEC branch circuit loads are calculated per 210.11, which points you to 220.10 in the 2023 NEC, which then points you to 220.41 and then you get your answer yes you use 3VA per sq ft if its a one-family, two-family or multifamily dwelling and the lighting and receptacles are described in items 1-3.
Click to expand...
And what about garages or those spaces not included as a dwelling because I see table 220.42(A), but those are for commercial right?
 
Some circuits can be zero, like bathroom 20A circuits, garages, and circuits for outside receptacles that arent serving inside too.

Doing a resi panel load schedule with VA loads marked like a commercial panel is kind of silly. Id just post the overall load calc and post that if needed.
 
Know that the panel calculations were revised downward in the 2026 code, to be more realistic.
You'll be quite safe with the 2026 calculations, assuming your jurisdiction will allow them.
 
suemarkp said:
Some circuits can be zero, like bathroom 20A circuits,
Click to expand...
If you go by the letter of the NEC for a branch circuit load of bathroom circuit one would need to use the area it serves 220.5(C) without overlapping with the area any other branch circuit serves. Say you have a 8' x 8' bathroom and its all on one 20A circuit then your load would be 64 SQFT x 3VA per SQFT = 192 VA.
If you have the lighting on a 15A general lighting circuit and just the GFCI's on a 20A bathroom circuit then I'd divide the room in two 64 Sqft / 2 = 32 SQFT x 3VA per sqft = 96 VA on each the bahtroom circuit and the lighting circuit.
suemarkp said:
Doing a resi panel load schedule with VA loads marked like a commercial panel is kind of silly.
Click to expand...
since the maximum area a 15A 120V dwelling branch circuit can serve is 600 sqft. I can see wanting to check it when doing remodel or addition to see what the load on existing branch circuits is..
 
1775497083664.png
This is what I am doing. The way I calculate for the lighting watts is take the area^2 and multply it by 3VA and them multiply it by 1.25 and for the receptacle I take amount of recepltacles and multiply it by 180VA. But am not sure how to do it for the exterior and garage as I am in the design phase and don't have the fixture wattage or amps. Is the way I am doing it right or should I be diong it another way?
 
Is that spreadsheet set up for Canada? Your equipment grounds in the US need to follow 250.122, also the 3VA already includes the 125% you dont need to add anything.
 
Correct, he is not in the USA. Besides the EGC sizes, the conduit is shown as 25MM.
 
roger said:
220.11
Click to expand...
Did you mean 220.14 (or did this move between 2023 and 2026)? I didn't realize that 220.14 covered all occupancies except for subpart (J) (and (G) and (H) wouldn't apply to a dwelling). That seems to cover outlets whether they have a specific load, a generic receptacle at 180VA per duplex, and only applies outlets not covered in the general lighting 3VA/foot rule.
 
tortuga said:
If you go by the letter of the NEC for a branch circuit load of bathroom circuit one would need to use the area it serves 220.5(C) without overlapping with the area any other branch circuit serves. Say you have a 8' x 8' bathroom and its all on one 20A circuit then your load would be 64 SQFT x 3VA per SQFT = 192 VA.
If you have the lighting on a 15A general lighting circuit and just the GFCI's on a 20A bathroom circuit then I'd divide the room in two 64 Sqft / 2 = 32 SQFT x 3VA per sqft = 96 VA on each the bahtroom circuit and the lighting circuit.

since the maximum area a 15A 120V dwelling branch circuit can serve is 600 sqft. I can see wanting to check it when doing remodel or addition to see what the load on existing branch circuits is..
Click to expand...
Semms kind of convoluted. What do you do in a laundry or kitchen when you have receptacles with a specified load calc but yet must still have a general lighting circuit for the lights? How much square footage is the lighting circuit covering since most of the receptacles are covered by the 1500VA rule.
 
suemarkp said:
Did you mean 220.14 (or did this move between 2023 and 2026)? I didn't realize that 220.14 covered all occupancies except for subpart (J) (and (G) and (H) wouldn't apply to a dwelling). That seems to cover outlets whether they have a specific load, a generic receptacle at 180VA per duplex, and only applies outlets not covered in the general lighting 3VA/foot rule.
Click to expand...
No, I meant 220.11 which confirms garages are not included.
 
brycenesbitt said:
Know that the panel calculations were revised downward in the 2026 code,
Click to expand...
Service and feder load calcs were downsized to 2VA per sqft and that is very welcome change!
However in the NEC dwelling branch circuit load calculations are different than service or feeder calcs, and the 3VA per sqft I *think* stayed the same in the 2026 for branch circuit load calcs.
So as others mentioned adding up a bunch of branch circuit calcs in a spreadsheet is not the same result as a 220.82 optional dwelling feeder or service calc.
For example a residential water heater, the branch circuit calc will add a continuous factor to the nameplate (load * 125%) but the service calc does not automatically kick that adder on (100% of load). There is more load diversity on a service or feeder so the calcs are different.
 
tortuga said:
I was commenting on the ground wire size it looks Canadian
Click to expand...
Yes the CEC did not change the EGC size for circuits 30 amps or less like the NEC did in the late 60s. When I was working at a hardware store while in high school in the mid 60s, 12 AWG NM had a 14 AWG EGC.
 
You must log in or register to reply here.
Top