Questions about adding sub panel to attached garage

[mjf]

No, not in terms of load calculations. See Smart$'s post #14 (specifically... 220.12: For dwelling units, the calculated floor area shall not include open porches, garages, or unused or unfinished spaces not adaptable for future use.)

Oops...thank you.:slaphead:

 

[Smart $]

The OP states ATTACHED garage....it is, in this case, part of the dwelling unit anyway.....right?

No, not in terms of load calculations. See Smart$'s post #14 (specifically... 220.12: For dwelling units, the calculated floor area shall not include open porches, garages, or unused or unfinished spaces not adaptable for future use.)

Oops...thank you.:slaphead:

However, I'd be willing to bet most service calculations for residences with an attached garage do not add in any general loads (lighting, general-use receptacles) specifically for the garage.

 

[Dennis Alwon]

However, I'd be willing to bet most service calculations for residences with an attached garage do not add in any general loads (lighting, general-use receptacles) specifically for the garage.

And I would bet that adding it in would not change the calculation much at all. I have been doing resi work for over 30 years and I bet I have done less than a dozen calculations for services. Probably less than half dozen...

 

[Smart $]

And I would bet that adding it in would not change the calculation much at all. I have been doing resi work for over 30 years and I bet I have done less than a dozen calculations for services. Probably less than half dozen...

Then there's that too

 

[kwired]

However, I'd be willing to bet most service calculations for residences with an attached garage do not add in any general loads (lighting, general-use receptacles) specifically for the garage.

That is correct, the attached garage general lighting load is already covered by the general lighting calculations (for service calculations). Now we want to run a feeder to supply this garage that already has a zero general lighting calculation already included in the service load calculation, how do we calculate the load for the feeder?

500 square feet x 0 VA = 0. Guess we don't need conductors for the feeder if all that is supplied is general lighting circuits.

How do we determine load for any circuit in a dwelling that would supply loads in the areas we don't need to include in the square footage mentioned in 220.12?

 

[Smart $]

That is correct, the attached garage general lighting load is already covered by the general lighting calculations (for service calculations). Now we want to run a feeder to supply this garage that already has a zero general lighting calculation already included in the service load calculation, how do we calculate the load for the feeder?

500 square feet x 0 VA = 0. Guess we don't need conductors for the feeder if all that is supplied is general lighting circuits.

How do we determine load for any circuit in a dwelling that would supply loads in the areas we don't need to include in the square footage mentioned in 220.12?

We'd have to do it as David instructed... but its perplexing exactly because of what you wrote.

 

[david luchini]

500 square feet x 0 VA = 0. Guess we don't need conductors for the feeder if all that is supplied is general lighting circuits.

How do we determine load for any circuit in a dwelling that would supply loads in the areas we don't need to include in the square footage mentioned in 220.12?

I think this is a case of 220.12 doesn't say what you think it says. (Obviously there is nothing that tells you to use 0 VA/sf for a lighting load.)

220.12 tells you the MINIMUM lighting loads for the SPECIFIED occupancies. If the load calculated for the Luminaires in 220.14(D) is greater than the minimum lighting load from 220.12, then the load from 220.14(D) is the calculated lighting load. If the load calculated for the Luminaires in 220.14(D) is less than the minimum lighting load from 220.12, then the load from 220.12 is the calculated lighting load. If the occupancy is not specified at all in 220.12 (such as the dwelling unit garage) then 220.12 doesn't apply at all, and the lighting load is calculated per 220.14(D).

 

[Smart $]

I think this is a case of 220.12 doesn't say what you think it says.

220.12 doesn't exactly say what you think it does either. Table 220.12 lists types of occupancies. A residential attached garage is part of a dwelling unit occupancy. Considering AHJ issuance of a CoO, is it for the entire structure, or the living quarters only, excluding the garage? The CoO covers the entire structure...including the garage.

 

[david luchini]

220.12 doesn't exactly say what you think it does either. Table 220.12 lists types of occupancies. A residential attached garage is part of a dwelling unit occupancy. Considering AHJ issuance of a CoO, is it for the entire structure, or the living quarters only, excluding the garage? The CoO covers the entire structure...including the garage.

Sure it does. It says that the MINIMUM lighting load for the SPECIFIED occupancies shall not be less than the unit load specified in Table 220.12. If further says that for dwelling units, the calculated floor area shall not include the garage. The CoO is not relevant to the branch circuit, feeder or service calculations.

 

[Smart $]

Sure it does. It says that the MINIMUM lighting load for the SPECIFIED occupancies shall not be less than the unit load specified in Table 220.12. If further says that for dwelling units, the calculated floor area shall not include the garage. The CoO is not relevant to the branch circuit, feeder or service calculations.

Yes 220.12 says the area of the garage is not to be included in the calculation... but it does not say the general illumination (and general-use receptacles) service load of the garage is not included in the result. Other than that, I agree with your assessment that we have to determine subpanel loading for a garage's illumination and general-use receptacles using 220.14(D) & (I).

 

[kwired]

I think this is a case of 220.12 doesn't say what you think it says. (Obviously there is nothing that tells you to use 0 VA/sf for a lighting load.)

220.12 tells you the MINIMUM lighting loads for the SPECIFIED occupancies. If the load calculated for the Luminaires in 220.14(D) is greater than the minimum lighting load from 220.12, then the load from 220.14(D) is the calculated lighting load. If the load calculated for the Luminaires in 220.14(D) is less than the minimum lighting load from 220.12, then the load from 220.12 is the calculated lighting load. If the occupancy is not specified at all in 220.12 (such as the dwelling unit garage) then 220.12 doesn't apply at all, and the lighting load is calculated per 220.14(D).

I agree with your explanation. 220.12 includes the general lighting portion of this garage in the calculation for the service or feeder to the dwelling, just happens to be part of the 3 VA ft² but the area of the garage is not counted. Now if you are supplying a branch circuit or feeder to the garage you have to use something other than 220.12 to determine the load - 220.14 is next place to go.