Residential load calc

[nizak]

In an existing install,at what value would a sub feed to an outbuilding be calculated at?

I have an existing dwelling with a 150A 120/240 V service and the house load equates to just under 90 amps.

There is a 100 amp sub feed to an outbuilding. The current load is 1 overhead door opener, and 8 8' Florescent strips. There are general purpose receptacles installed but no load to speak of.

The home is for sale and a perspective buyer is telling the agent the electrical is undersized.

I'm sure if someone were to use the building for a shop (welder, saw, possible electric heater, etc) there could be a concern, but I can't see having to currently figure it at 100 A.

Thanks

 

[kwired]

In an existing install,at what value would a sub feed to an outbuilding be calculated at?

I have an existing dwelling with a 150A 120/240 V service and the house load equates to just under 90 amps.

There is a 100 amp sub feed to an outbuilding. The current load is 1 overhead door opener, and 8 8' Florescent strips. There are general purpose receptacles installed but no load to speak of.

The home is for sale and a perspective buyer is telling the agent the electrical is undersized.

I'm sure if someone were to use the building for a shop (welder, saw, possible electric heater, etc) there could be a concern, but I can't see having to currently figure it at 100 A.

Thanks

Don't know if general lighting should be based on dwelling units since it is a dwelling accessory building or not, but worst case I see it should be 3 VA per square foot plus the garage door opener - which might be ~500VA up to maybe 1000.

So a 20 x 20 shed maybe only 2000 VA or so. Doesn't matter that your 100 amp circuit potentially could deliver 24000 VA - the load simply isn't there. In many ways this is no different they supplying the house that only has a 90 amp load calculation with a 400 amp service. As is it is not undersized. If the perspective buyer wants to add a bunch of load to the shed it may be undersized but only when that happens. IMO this should not be an issue for the seller, unless it is a "build to suit" type of deal.

 

[nizak]

I'm almost certain that in the end this is all a part of getting the house at a cheaper price since the electrical will neede to be " upgraded" if purchased.

Go back in a year and you'll find the existing service working just fine.

JMO

 

[al hildenbrand]

Don't know if general lighting should be based on dwelling units since it is a dwelling accessory building or not, but worst case I see it should be 3 VA per square foot.

220.12 instructs us not to use the floor area of garages in calculating the General Lighting Load of a dwelling.

220.83 instructs us to use the nameplate rating of the existing garage door opener. That's it.

The buyer claiming the existing electrical service is undersized is just plain wrong, and should be challenged by requesting the buyer to show their calculation / evidence of that claim. Providing your calculation will show the buyer what the NEC requires, and, after they educate themselves, will probably dispel this attempt to manipulate the seller.

 

[kwired]

220.12 instructs us not to use the floor area of garages in calculating the General Lighting Load of a dwelling.

220.83 instructs us to use the nameplate rating of the existing garage door opener. That's it.

The buyer claiming the existing electrical service is undersized is just plain wrong, and should be challenged by requesting the buyer to show their calculation / evidence of that claim. Providing your calculation will show the buyer what the NEC requires, and, after they educate themselves, will probably dispel this attempt to manipulate the seller.

Exaclty why I said I wasn't sure if dwelling calculations applied - this is a dwelling accessory yet isn't exactly a dwelling either.

So in your opinion if we have a huge shed here maybe 2500 square feet and all we have is lights (maybe several high bay type fluorescents) and a door operator or two are you saying the only load NEC requires us to account for is the door operators? That may only result in a thousand or two volt amps even though the lights may be 4 or 5000 volt amps.

I said the worst case would be to use 3 VA per square foot (what else is in 220.83 that would apply to this building that would be any higher?) and still came up with pretty minimal load (for a small shed anyway) compared to the 100 amp feeder capacity.

I come across many "man sheds" that have just as much if not more load then the dwelling they are an accessory to anymore, yet NEC doesn't really address how to calculate this load, unless you can actually call the space a separate dwelling.

 

[al hildenbrand]

Kwired,

The OP says there is nothing in the structure except receptacles and lights. a garage door that is operable with a fastened in place opener.

If it walks and quacks like a duck, it probably is a duck. (garage).

The buyer needs to substantiate their claim, in the face of the Article 220 calculation provided by the evaluating electrical professional (the OP). What the buyer wants to do in the future does not make the existing structure inadequate by Code. It may be inadequate to the buyer, but that is not the seller's burden, unless the seller NEEDS to accept the burden for non-Code reasons.

And, looking back at the exact question in the OP, the existing feeder to the outbuilding is not a load, nor does it have any place in arriving at the "calculated load".

As a selling point, to entice the buyer, the existing feeder speaks to the already-in-place electrical capacity for future expansion . . . that is not a liability, or deficiency, but a selling point feature. The load calculation done by the OP demonstrates the unused capacity presently available for expansion in the future. That's all positive for the SELLER.

 

[kwired]

Kwired,

The OP says there is nothing in the structure except receptacles and lights. a garage door that is operable with a fastened in place opener.

If it walks and quacks like a duck, it probably is a duck. (garage).

The buyer needs to substantiate their claim, in the face of the Article 220 calculation provided by the evaluating electrical professional (the OP). What the buyer wants to do in the future does not make the existing structure inadequate by Code. It may be inadequate to the buyer, but that is not the seller's burden, unless the seller NEEDS to accept the burden for non-Code reasons.

And, looking back at the exact question in the OP, the existing feeder to the outbuilding is not a load, nor does it have any place in arriving at the "calculated load".

As a selling point, to entice the buyer, the existing feeder speaks to the already-in-place electrical capacity for future expansion . . . that is not a liability, or deficiency, but a selling point feature. The load calculation done by the OP demonstrates the unused capacity presently available for expansion in the future. That's all positive for the SELLER.

Nearly exactly my thoughts as well, though the existing feeder is not itself a load, it does supply some load of some sort.