In Canada we'd use #3 copper for 100A. I believe in the US most would recommend #2 copper. 1 1/4" is the bare minimum for 100A #3. Because of the long run you can expect loss. If you want 100A you'll likely need 1/0 which won't fit in 1 1/4".

Most areas in the US allow the use of table 310.15(B)(6) which would size the conductor at #4cu or #2al.

Because of the distance, and the fact that you will have larger motor loads out there, you may want to bump it up to #3cu. IMO #2cu is unnecessary overkill.

IMO, only by the most liberal of interpretations would Table 310.15B(6) apply to this feeder. A shop or outbuilding is not a dwelling.

#3 copper conductors should be adequate for your needs.

"A shop or outbuilding is not a dwelling."

No, not specifically, but if part of a dwelling property it IS most definitely considered a dwelling accessory building and falls under dwelling rules.

And as far as "the most liberal of interpretations", do a national survey of electricians and see what you come up with.
Yes, some area's AHJs do not allow this. From the feedback I have seen over the years on these boards most do.
Why would they not?
What is the difference between a main 100 amp service and a 100 amp sub-panel in so far as the likely load is concerned? NOTHING. So why would you require a larger size wire to one than the other???

Interesting about your feeder sizing. In Canada 100A main or sub requires #3 copper by code. That's why I suggested one size thicker at #2 for 150'.
Either we're more stringent, or you're more liberal, or both!

The guy at Lowes mentioned using aluminum instead of copper since it's less expensive (About a fifth of what copper costs). Is aluminum a viable option? If so, what is max size to fit the 1-1/4" PVC and what amp service would it provide? Thanks for all your input, most informative!

I would definitely check with a electrical supply house and compare the prices against Lowes or H Depot. Recently I did and found the price was 1/2 the cost at the supply house. HD might have decent prices on things like romex, but when it comes to getting something cut off a spool, I would be careful.

Petey,

If you've done the national survey, can you post a web address where I can peruse it? I'll post the question on a few of the boards I visit to see what others think.

Heres a what if question for your interpretation: if AFCI protection should become required for all circuits in a dwelling in the upcoming 2008 NEC, would AFCI protection be required for branch circuits this outbuilding? Assume that there would be no language aboiut habitable areas, etc..

Cheers

Tom

No, I have not done a formal survey. I have though been coming to these electrical boards, many of them, for years now. The feedback I have seen is what I base this on.

An answer to your question would be hard without the actual wording of the new code requirement.
Let's just say I hope they do NOT pass this requirement!

It looks like Arc Fault protection will be required for all 15 and 20 amp circuits in a dwelling unit (proposal was accepted by a vote of 8 to 4) . So if thats the case, an inspector that allows a feeder size based on 310.15(B)(6) to feed an outbuilding, then to be consistent, maybe arc fault protection will be required for the branch circuits in outbuildings.

There was also a proposal that was accepted in principle that would change the language of 310.15(B)(6) to something everyone should be able to understand.

To paraphrase Mark Twain- an electrican that does not read the code is uninformed and an electrician that does read the code is confused.

I talked to more electricians than I can shake a stick at about this issue, because I basically needed to do the same type of thing. We added an addition onto our house, and the main panel is a good 60 feet from the new subpanel. I wasn't sure what wire to use, but I gathered from numerous electricians that if I wanted 100 amp service drawn into that subpanel (I have 200 amps at the main), then just get the aluminum AWG2 wire, run a ground along with it, stick it in some pvc conduit, conduit it straight into the sub panel, and you're good to go. I used 1 1/2" conduit (I know, overkill, but it sure was nice to not have to actually pull the cable -- it just slithered right through). So anyway, I hope all those electricians weren't jerking my chain.

I'M WIRING A DETACHED GARAGE AND THERE IS A #6 WIRE ALREADY RAN TO A #50 AMP PANENEL BOX IN THE GARAGE. THE WIRE UNDERGROUND IS IN PIPE AND HAS BEEN CUT. CAN I REATTACH THE WIRERS AND PIPE UNDERGROUND AND CONTINUE THE WIRE RUN TO THE GARAGE????