detached garage load calculation

[difowler1]

I have a residential project. The calculated load is 179 amp using the alternate method. The customer wants a detached garage with a 100amp service. It won't be a separate service with a 2nd meter. I am wondering how I would accurately add the load of the detached garage to the house.

I don't know what he is actually planning on running in the garage. He doesn't know yet, but he knows he wants 100amps for the garage. Would I need to guess how much (lighting, a possible welder, water heater, an hvac) he would have? Or if I were to suppose he would at some point use 90 of his possible 100amps in the garage, would I list that 90amps with the appliances etc. as a 21,600 watt load on the calculation with the house?

dean

 

[kwired]

I have a residential project. The calculated load is 179 amp using the alternate method. The customer wants a detached garage with a 100amp service. It won't be a separate service with a 2nd meter. I am wondering how I would accurately add the load of the detached garage to the house.

I don't know what he is actually planning on running in the garage. He doesn't know yet, but he knows he wants 100amps for the garage. Would I need to guess how much (lighting, a possible welder, water heater, an hvac) he would have? Or if I were to suppose he would at some point use 90 of his possible 100amps in the garage, would I list that 90amps with the appliances etc. as a 21,600 watt load on the calculation with the house?

dean

If you want to be covered should those items get added later - yes.

That said welder can almost be ignored unless maybe he plans to use it for commercial like production on a daily basis and it has high duty cycle or there are multiple welding machines in heavy use - but we are probably talking hobby and other minor projects I would guess. Same for many other power tools. At dwelling garages they seldom use more then a couple items at a time unless there is some serious production going on with multiple people using the machines, and even then if it is residents of the dwelling - that probably means there isn't much going on in the house so the house load is low when the garage is busy.

HVAC and other loads that run automatically whether occupied or not are the ones that add more of a true load you need to give serious consideration to the dwelling load when the garage is supplied by the dwelling.

I can't tell you your AHJ will see it that way if that is what you are asking about.