Detached Residential Garage Load Calc.

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Dennis Alwon

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Chapel Hill, NC
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Retired Electrical Contractor
Thanks for the tip. That is where I have been looking though. It appears that I have to calculate 180VA for each receptacle in the garage?

Honestly I rarely need to do a calculation for resi work. What are you wiring in the garage? A few outlets? Are you adding a panel?
 

suemarkp

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Kent, WA
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Retired Engineer
I think you could argue that the load calc is zero. 220.14(J)(2) which references 210.52(G), specifically exempts attached/detached garage outlets, at a single family dwelling. It says they are included in the 3VA persquare foot calculation. Strange thing is, that square footage specifically eliminates the garage.

If there are other circuits in the garage (something other than general use receptacles), then those would be part of the feeder calculation. Basements and bathrooms are they same way -- no calculated load. Good design practice says to assume a load of 15A for the 120V circuits when sizing your feeder (but you couldn't install anything smaller anyways).
 

Ravenvalor

Senior Member
What are you wiring in the garage? A few outlets? Are you adding a panel?

I am installing 15 - convenience receptacles, 2 - garage door opener receptacles, & 3 - 8' 2lamp strip lights for the unfinished portion. I am installing 1 - overhead light and 4 - convenience receptacles for the finished portion, & 1 - 2lamp flood light on the outside. I will install 1 - electrical panel in the finished portion.

Suemarkp is leaving me to believe, especially after reading 210.52(g) I probably should calculate the load at 3VA per sqft.

Thanks,
 

Dennis Alwon

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Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I am installing 15 - convenience receptacles, 2 - garage door opener receptacles, & 3 - 8' 2lamp strip lights for the unfinished portion. I am installing 1 - overhead light and 4 - convenience receptacles for the finished portion, & 1 - 2lamp flood light on the outside. I will install 1 - electrical panel in the finished portion.

Suemarkp is leaving me to believe, especially after reading 210.52(g) I probably should calculate the load at 3VA per sqft.

Thanks,

Are you trying to find out if the house panel can handle it? I would just run a 60 amp wire out there and be done with it in case they want a/c ,etc at some point.

I am sure a 30 amp circuit would work just fine for what you have. I really don't think there is a clear answer to your question in the nec. It is not a dwelling unit so I don't see 3watts / sq.ft as being necessary but it may be the easiest method.
 

Ravenvalor

Senior Member
The AHJ is a little difficult to work with, plus the homeowner went into their office and ticked them off. I may need to just let the homeowner hire an engineer to draw and seal a set of plans in order for this bird to fly.

Thanks for the help.
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
Treat the garage door opener(s) as fastened-in-place equipment. I think that is the only thing the inspector can require in a load calc. There is no code required value for garage lighting in a dwelling, but since you know what it is I'd add it to your calculation (nothing wrong with listing things on a load calc that aren't required to be there). But I don't think the homeowner will be happy with just that if there are really 15 convenience outlets.

You say you're installing a feeder. I would think a 20A 120/240V feeder would be the minimum that would work well. I'd go with at least a 30A feeder and perhaps more depending on what the homeowner wants in this garage. It will be the future fastened-in-place (or semi stationary) equipment that will drive up the feeder load calc (an electric vehicle charger could be a rather huge number as could welders or air compressors). Leaving room for growth will make the next electrician happy.
 

Ravenvalor

Senior Member
Leaving room for growth will make the next electrician happy.

Leaving room for growth will make the next electrician happy.

"Leaving room for growth will make the next electrician happy"

I definitely agree with you on that account.
 
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