just built a shop and am running a line from main panel to shop. the run is about 85'. i will be putting in a single.220v outlet, about 8 110v outlets and some led ligjts. i want to put a subpanel in as well. currently i have a 200 amp service with a lot of room to spare for this. I was told 3/o is what i should run. does that sound right?
determining size of wire
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pattenp
Well-known member
Anticipated max amp load determines the feeder size. 3/0 Cu is 200A which is a lot of power for a shop unless you have some power hungry equipment, heating, A/C, etc. What is your anticipated max load at one time? I'll dare to say you can get by with 60A which is #6 Cu.
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3rdgendslmech
Well-known member
Sounds about like my plan. I want to run 100 amp to my shop 100' away. As long as you're the only one working in your shop you could probably get by with running 2 2 2 4 aluminum. Not to sure on the length of your run, but I was told due to length of run and wire size it's de-rated to 90 amps.
ard
Well-known member
Yikes.
Time to stop listening to whomever it was that told you this.
You really should take a moment and consider 'how much power MIGHT I need an 10,20 years with everything I might be doing in the shop?"
Heat, AC, waterheat? Plus whatever tools and equipment you have.
Yes, 60A might do it. but so might 90. We cant decide- only if you outline your potential uses can we give it a ballpark
sberry
Banned
90 is cheaper,,, ha
wyliesdiesels
Well-known member
If this is a one man shop, 3/0 would be super overkill.
#2 al MHF would get you by just fine on a 90a breaker...
The 90a limitation doesnt have anything to do with length but instead ampacity rating of #2 al for branch feeders for anything but a dwelling.
wyliesdiesels
Well-known member
3/0 is way overkill then.
#2 al MHF is your best bang for the buck....
#2 al MHF is your best bang for the buck....
ddawg16
Well-known member
As a metric......
I have 50A 240Vac going to my garage....about 50' of wire. I'm using 6awg THWN in conduit. All of this goes to an 8 slot 60A sub...but I'm only use 6 breakers. (anything over 6 requires a main breaker in the panel...and that's my story and I'm sticking to it).
I have a 240Vac compressor....18 recessed cans with LED's. Lots of outlets.....240Vac outlet for a welder....lots of fixed power tools....table saw, radial arm saw, compound miter saw, etc, etc.
I've never tripped a breaker.
I have 50A 240Vac going to my garage....about 50' of wire. I'm using 6awg THWN in conduit. All of this goes to an 8 slot 60A sub...but I'm only use 6 breakers. (anything over 6 requires a main breaker in the panel...and that's my story and I'm sticking to it).
I have a 240Vac compressor....18 recessed cans with LED's. Lots of outlets.....240Vac outlet for a welder....lots of fixed power tools....table saw, radial arm saw, compound miter saw, etc, etc.
I've never tripped a breaker.
Crazyjake8493
Well-known member
As mentioned, 2-2-2-4 mobile home feeder is your best and cheapest option. I ran it to my garage fed by a 60amp breaker since I already had that, and didn't want to spend the extra on a 70 or 90a at the time. Haven't needed to up the breaker size, but can go up to 90a if I ever need to in the future.
When shopping for MHF, make sure it is actually MHF (2 black, white, green) and not URD which is all black cables with phase markings and a yellow stripe. MHF carries a RHH/RHW-2 insulation rating, which allows it to be brought inside the structure (in conduit), URD does not have that rating and must be transitioned to 2-2-2-4 SER when entering the structure.
Don't rely on a supply house to give you the correct stuff, double check it yourself. I had two different guys try to give me URD when I asked for MHF.
When shopping for MHF, make sure it is actually MHF (2 black, white, green) and not URD which is all black cables with phase markings and a yellow stripe. MHF carries a RHH/RHW-2 insulation rating, which allows it to be brought inside the structure (in conduit), URD does not have that rating and must be transitioned to 2-2-2-4 SER when entering the structure.
Don't rely on a supply house to give you the correct stuff, double check it yourself. I had two different guys try to give me URD when I asked for MHF.
With a true 90A load, a 3% voltage drop can be realized at ~135' total feeder length w/ 2 2 2 4 Al. 3% and lower is a good design.
At 100', VD is a non-issue. More likely, you will never reach a 90a load.
Even less of a concern at 85'.
Also consider 2-2-4-6 MHF if you can find it easily.
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sberry
Banned
I like that mm pointed out some difference in length and that it really only applies to high load. So many calcs appled to the breaker size and not actual, as dawg said, doent trip a 50 and so many general are estimated at 20A at 100 ft when the max is closer to 13A intermittent at 60 ft and many significantly less.
This is the beauty of number 2 for garage wire, V drop is rarely a concern.
This is the beauty of number 2 for garage wire, V drop is rarely a concern.
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pattenp
Well-known member
If you're asking for the 2-2-2-4 MHF then yes, 2" is good.
BTW, you didn't specify whether it was 3/0 CU or AL that was recommended. Even AL is way overkill as it is good for ~150A.
Yeah 3/0 cu would be a big waste of $$$.
Start identifying all loads: name, full load kws, capable of less than full load(how much), which run simultaneously, seasonal, etc.
ard
Well-known member
Whatever wire you need for 80, will also get you 90....
The #2 everyone is suggesting will get you 90.
Going to 100, so 10 more, will force you to jump up in size.
Hence the question is 'can I get by with 90, or do I need 100?'
Almost certainly the answer is 90.
