Garage Subpanel feeding new Barn

[MarkInIowa]

First post! I've read through lots of posts on Garage Journal and others. Very good information and I want to run my electric plan by those with experience here.

Background
I have two detached buildings on my property: a 3+ car garage and a new 30x40 pole barn. I'll refer to these as the "garage" and the "barn".

• House - 200A service
• Garage - currently fed by approximately 100ft of 6ga copper stranded wire (4-wires in conduit) protected by a 60A breaker in the house. This is my primary shop and work area. I have a small welder and air compressor that I use occasionally, but no other large loads. Mostly I am doing woodworking and light automotive projects. I have never tripped the 60A breaker.
• Barn - this is a new 30x40 pole building with no electric service yet. This building will mainly be cold storage, however I would like electricity for basic lighting, battery maintainers, security cameras (light loads). I want to plan for the future but without going overboard - especially with current wire prices.

It's only me working in these buildings, so I don't anticipate multiple loads running at the same time.

My proposal & questions:
I am planning to run power from the panel in my existing detached garage to the new barn. Running power direct from the house would be farther, and in addition there are several obstacles in the way (septic, gas line, and tree roots). It's 324ft from my existing garage panel to where the new barn panel will be. About 275ft of this will be buried in conduit and the other 50ft running in conduit inside the garage.

Based on my research I am thinking of running either 6ga stranded copper or 2/2/2/4 aluminum USE-2 Mobile Home Feeder in 1-1/2 conduit. According to the Southwire voltage drop calculator, both of these options would only allow 20A at my barn.

My questions are:

1. Can I really only get 20A out of 6ga copper or 2/2/2/4 aluminum at this distance? The guys building my building are currently using 300ft of 16ga cheap extension cords to run their compressor and chargers. I'm not saying that's right, but it seems crazy that I would need such larger wires for the panel.
2. I've done a lot of wiring with copper, but never aluminum. Any reason not to go with aluminum in this application?
3. Any issue with running PVC conduit inside the garage and through the attic?

 

[pattenp]

You will be okay at 30A with #2 Al. 40A is pushing it.

 

[wyliesdiesels]

Be weary of online VD calculators especially those created by a wire manufacturer...

There is a voltage drop calc in the electrical FAQ sticky that you can use to do the calcs yourself

2. aluminum would work just fine over copper and will save you some money

3. no issue code wise

 

[pattenp]

Don't forget to include that 100ft of #6cu along with the 324ft of #2al when calculating the VD. The pvc conduit is fine inside and in the attic.

 

[MarkInIowa]

Thanks for your responses. I'm planning to pick up the 2-2-2-4 MHF tomorrow. I'm running the MHF in PVC conduit from the feed panel up through the attic, down the wall, and underground to the new building (2-2-2-4 MHF in conduit all the way from old panel to new panel). I think I have everything I need except the breaker for the panel from which I'm feeding the new building.

Looking at "THQL" breakers for my GE panel, the 30A and below breakers accept 14 to 8 AWG wire (35A+ breakers accept 8-3AWG). Reading some past posts on Garage Journal I see recommendations to use a splicer/reducer to fit a larger wire to a relatively smaller breaker. In my case would I splice the #2 MHF to a #8 in the panel to join to the breaker? Is that acceptable? That seems like a pretty big step down in wire size. Would I be better off going with the 35A breaker to have a larger lug size?

 

[pattenp]

As long as the splice/reducer is listed for the wire sizes it's no problem. You can go with the 35A if the lesser wire size reduction makes you feel better.

 

[MarkInIowa]

Thanks pattenp.

How long should the "jumper" wire be between the splicer/reducer and the breaker? I would think it would be best to keep that as short as possible since it would be a current-limiting section.

 

[pattenp]

As short as possible is best but not critical.