Feedback on Feeder to detached garage

[sw_ross]

Normally we just run 2-2-4 URD to a detached garage fed with a 100amp breaker to a 22space Main Breaker panel. That covers most needs that a typical garage has (in our area at least).

The garage I'm starting tomorrow, however, has a little apartment in the back section of the garage. Garage footage is 42x36 with the apartment in the last 14 feet (14x36). It has a bedroom, bathroom, and sitting area. The garage will have a 5kw shop heater, there's a 4.5kw water heater, and about 4kw of heat in the apartment area. They also want a 50amp rv receptacle, and a 30 amp rv receptacle (separate from each other).

We're at about 60 amps of just heat (including water heater). Other than what I've already mentioned there will be just general purpose receptacles in garage and apartment area.

I'm thinking we need to go up a bit in feeder size, but not sure how to handle this load calculation. Any feedback would be greatly appreciated.

Sky

 

[Buck Parrish]

Well your most common next size direct burial is 4/0-4/0-2/0 AL. Other wise you will have to use conduit.

 

[kbsparky]

No equipment ground? :-?

 

[Dennis Alwon]

No equipment ground? :-?

It depends on which code cycle they use. It may be legal but you knew that.:grin:

 

[sw_ross]

We haven't gone to the 2008 code yet, so we usually use 250.32(B)2 under the 2005 code to bond the grounded conductor to the grounding system.

Sky

 

[don_resqcapt19]

We haven't gone to the 2008 code yet, so we usually use 250.32(B)2 under the 2005 code to bond the grounded conductor to the grounding system.

Sky

With the apartment in the garage, it is likely that there are other conductive paths between the two building and that would require the installation of a cable with an EGC.

 

[augie47]

after we hash all that out, perhaps we should discuss the "URD" :smile:

 

[raider1]

Normally we just run 2-2-4 URD to a detached garage fed with a 100amp breaker

A detached garage is not a dwelling therefore you can't use Table 310.15(B)(6) to size the feeder. #2 Aluminum at 75 degrees C is good for 90 amps before the application of any adjustment factors. 90 amps is a standard size breaker so you can't use the next size up rule of 240.4(B). This is a common violation in my area.

Chris

 

[LarryFine]

Normally we just run 2-2-4 URD to a detached garage fed with a 100amp breaker to a 22space Main Breaker panel.

I hope that's copper URD, because #2 al isn't large enough for 100a on anything other than a service main.