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SRedinbo 04-30-2011 11:35 PM

Correct type of wire for a 100 amp, 160 ft run
I'm currently converting a 10'x20' outbuilding on my property to an office. Imagine my surprise when I can only find 1 lonely 12-2 wire leaving my basement headed that direction. After further investigation, I have two outbuildings over 100ft from my box (the one I'm converting, and a two car garage) with a total of 8 light receptacles, and 20 outlets, running off of that wire.

Because of the increased load (computers, lighting, AC) associated with my remodel, my plan is to install a 100 amp box in one of the buildings, and run 4-6 circuits off of it. Because of obstacles, the run from that 100 amp box to the box on my basement is approx. 160 ft. According to my research, it appears that three wire direct burial service wire, 1/0, aluminum, is what I need. Problem is, the nearly $2/ft price tag puts a squeeze on the project budget. Do I really need wire this strong, or would something else work?



Saturday Cowboy 05-01-2011 12:19 AM

you will have to go 4 wire. the exception was removed from the last code change.

100a - 3ga cu or1/0al THWN in PVC conduit.

Do you actually need 100a?? say 60a will save u a lot o money.

SRedinbo 05-01-2011 12:26 AM

Yeah, I just saw the 4-wire issue in another post. Must have missed that requirement somewhere.

I have a bad habit over over engineering everything, especially when it comes to electricity. I always want to leave room for expansion, especially in this case when I may do some landscape lighting in that area. If 60 amp service would leave me that kind of wiggle room, what size of 4-wire would I need for that run?

Saturday Cowboy 05-01-2011 12:30 AM

#6 cu 4Al

Saturday Cowboy 05-01-2011 12:32 AM

If this is going to be an office and you don't mind me speculating.

5a lighting
15a plugged in stuff
electric heat? 20a
windows ac? 18a
wont be using both those at the same time

outside lights don't pull much

frenchelectrican 05-01-2011 12:36 AM

As far for your office space will you have gaz heat or electrique heat ?? that will affect it as well.

If you go with gaz heat and standard A/C the 60 amp circuit will be plenty big for most case.

I don't know if you are aware of this or not but with resdential property if you have detached building and used for non commercal useage you have to use the AFCI but if this is zoned commercal then no you do not need AFCI at all.

I will suggest to bury a 1,5 inch conduit that is the minum size for that distance the reason why I suggest due in the future you may increase the conductor size if the 60 amp is too small for ya.

In the conduit you have to use the THHN/THWN copper or XLPE alum.

For 60 amp size you will use 16mm˛ Copper or 25mm˛ Alum *


* Note *
16mm˛= #6 AWG
25mm˛= #4 AWG

SRedinbo 05-01-2011 12:51 AM

Thanks for all of the info, guys!

Don't mind you asking about the office needs at all. The office-related stuff will be minor; 2-3 computers, a printer, a few lights. Me real concern in heat/AC. I really don't want to run gas out there, so heat will have to be electric. I'm currently considering something like this Mitsubishi system like this that will fulfill both needs.

The only thing in the garage that will run with any regularity is the door opener.

I wasn't aware of the AFCI requirement, either, but isn't that just a matter of getting the right breaker?

SRedinbo 05-01-2011 01:06 AM

Yeah, the last guy who owned this place was a real piece of work. He updated a bunch of the wiring, and snipped the ground in the process. He had the box stuffed with piggyback breakers, and hardly any of it was grounded. How this place didn't burn down, I'll never know. Small wonder it was a foreclosure!

NJMarine 05-01-2011 06:18 AM

type of wire
210.12 is only applicable to dwelling units and article 100 defines such as: "A single unit, providing complete and independent living facilities for one or more persons, including permanent provisions for living, sleeping, cooking, and sanitation, therfore an office in a detached garage would not require afci.

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