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Thread: 100amp Subpanel Wiring

  1. #1
    Join Date
    Jul 2017
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    Lancaster, PA
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    55

    100amp Subpanel Wiring

    Hey all,

    I made a post about a week ago regarding the electrical situation in my attached garage. To run all of my new power tools I'm going to need to run a 100amp subpanel into my garage (have a 200amp main breaker box).

    My question is regarding the wire I'll need? It's going about 35ft, and everything I've seen seems to indicate a 2 AWG conductor. The prices I've seen from the big box stores, e-stores, and Facebook/Craigslist seem to be all over the place, and many different types to choose from.

    The wire will be ran through a crawl space from the main panel to the subpanel. I was looking at this.... https://www.wireandcableyourway.com/...le-with-ground

    It comes to about $300 with tax + shipping, but I was really hoping to spend less. I have no problem going aluminum wiring which seems to be way cheaper, but wasn't sure if anyone could point me to a place that has good pricing?

  2. #2
    100 amp breaker
    Wire x distance
    100 amp box
    Underground pipe box...
    Connectors...

    Adds up. Sometimes you can get a deal on the box and breaker package...

  3. #3
    Join Date
    Jan 2021
    Location
    The Woodlands, Texas
    Posts
    343
    Its going to depend on the type of wire, copper/aluminum, how its enclosed, the temperature rating on it, and where its going to be located, etc. You would think it would be simple, but these differences make huge differences in the gauge of the wire needed.

  4. #4
    Join Date
    Mar 2010
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    Doylestown, Pa
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    14
    Scott, the price of wire is all over the place. A simple roll of 14-2 is now $120.00 I just priced 250 feet of 10-3 for my 3 phase machines. $430.00 at the big box stores. Ouch. I would bite the bullet I always go to the next level (gage) when doing electrical work. The copper will give you peace of mind.

  5. #5
    Join Date
    Feb 2014
    Location
    Lake Gaston, Henrico, NC
    Posts
    6,212
    If you're in a state where anyone off the street can buy from a dedicated electrical supplier, it will be a little over half the price of in box stores.

    I'm getting ready to direct bury, to a 125 amp subpanel 520 feet away, that will supply another 60 amp panel 260 feet down the line from that one. Talking big wires.
    I found some decent prices online, but none as good as my supplier.

    Make sure to measure the run carefully, before you buy the wire, and buy about 10 feet extra to have to throw away. Without the extra, you're about guaranteed to come up short. I dig trenches first, after learning that lesson the hard way.

    Edited to add: Do note that running it in conduit downrates the carrying capacity a significant amount.

  6. #6
    Join Date
    Mar 2003
    Location
    SE PA - Central Bucks County
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    59,290
    2-2-2-4 aluminum is what the licensed electrician used for my 100 amp sub in the temp shop. That was approved by the folks that processed the permit for my jurisdiction. I believe 3-3-3-5 copper is also kosher, but it's considerably more expensive.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  7. #7
    Join Date
    Feb 2008
    Location
    E TN, near Knoxville
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    11,459
    I use an online wire sizing calculators to figure sizes. Pay attention to the voltage drop.

    I put in copper 250' underground for to 100 amp box in my shop, wire calculated for a less than 1% voltage drop.

    Fortunately your distance is short. I ran 650' of #2 to underground to feed 230v power to another area of the farm. That was pricey.

  8. #8
    Quote Originally Posted by Jim Becker View Post
    2-2-2-4 aluminum is what the licensed electrician used for my 100 amp sub in the temp shop. That was approved by the folks that processed the permit for my jurisdiction. I believe 3-3-3-5 copper is also kosher, but it's considerably more expensive.

    Unless #2 AWG aluminum is supplying the ENTIRE load of a dwelling, it is limited to 90 amperes. The folks at the Garage Journal love 2-2-2-4 MHF (mobile home feeder) cable, because it's cheap & 90A is adequate for most needs.

  9. #9
    Join Date
    Sep 2016
    Location
    Modesto, CA, USA
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    6,705
    100 amps seems excessive to me. 80 amps would be adequate for most home shops. You do know that the breakers will add up to more then 100 amps? Off hand I would guess 20 amps each for tablesaw, ac/heat, compressor plus 15 amps for lights.
    Bill D

  10. #10
    I have 50 amps to my shop (single person) and never had a problem. When you're working by yourself, you're generally just running one tool and the dust collector.

    I put in a separate 100 amp subpanel for two 50 amp outlets for EV charging. I don't remember now what gauge wire I ran from the main panel to the subpanel but I think it was 2 copper. It was a short run, about 25 feet. EV's are designed to draw only 80% of the circuit rating. So when you plug an EV into a 50 amp outlet, it will only draw 40 amps (max). So even if I were to plug two cars in at the same time, the max current will be 80 amps.

    Mike
    Last edited by Mike Henderson; 10-30-2021 at 12:52 AM.
    Go into the world and do well. But more importantly, go into the world and do good.

  11. #11
    Join Date
    Jul 2005
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    Eastern Iowa
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    Quote Originally Posted by Rollie Meyers View Post
    Unless #2 AWG aluminum is supplying the ENTIRE load of a dwelling, it is limited to 90 amperes. The folks at the Garage Journal love 2-2-2-4 MHF (mobile home feeder) cable, because it's cheap & 90A is adequate for most needs.
    As you will be in a crawl space and not trenching I would go with 2-2-2-4 Aluminum SE-R rather than MHF. About the same price per foot ($1.94/ft and $1.67/ft respectively at our local menards). But SER can be run the same as generic romex (nm-b). With MHF you will need to buy conduit fittings and run it in conduit, definitely in the buildings before and after transitioning to and from the crawl space. Mhf can be direct buried, but must be in conduit inside. And, I seem to recall an inspector on Mike Holtís forum saying the crawl space is also considered part of the house envelope (that is why nm-b is allowed in crawl spaces). If so then everything must be in conduit.

    With SER you can sleeve it through the floor into the crawl space and staple it to bottom of the floor joists.
    But, nothing underground.
    Comments made here are my own and, according to my children, do not reflect the opinions of any other person... anywhere, anytime.

  12. #12
    Join Date
    Jul 2005
    Location
    Eastern Iowa
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    667
    Quote Originally Posted by Mike Henderson View Post
    I have 50 amps to my shop (single person) and never had a problem. When you're working by yourself, you're generally just running one tool and the dust collector.

    I put in a separate 100 amp subpanel for two 50 amp outlets for EV charging. I don't remember now what gauge wire I ran from the main panel to the subpanel but I think it was 2 copper. It was a short run, about 25 feet. EV's are designed to draw only 80% of the circuit rating. So when you plug an EV into a 50 amp outlet, it will only draw 40 amps (max). So even if I were to plug two cars in at the same time, the max current will be 80 amps.

    Mike
    As Mike says, you may be able to get by with 50 amps, but with the price of copper you can run 90 amps cheaper than 50.
    Lowes had 6-3/g Cu for $6.58/ft. ... times his 35ft = about $250
    2-2-2-4 SER @ 1.94/ft. .... ~$68. More than makes up for the $30 difference between a 50 amp breaker and a 90 amp.
    Comments made here are my own and, according to my children, do not reflect the opinions of any other person... anywhere, anytime.

  13. #13
    Yes, I agree with others 100A is not necessary unless you have a huge garage with a separate AC maybe.

    For over 25 years I ran my shop on 60A feed to my barn. That includes a big 5 HP compressor.

    One common misconception is that every 220v machine needs a dedicated circuit. I had an electrician wire my shop he put everything on one circuit. Table saw, planer, bandsaw (all 3HP), jointer (2HP). Right or wrong Ive never has an issue.

    As always, if your a DIY electrician, I strongly recommend you leave the heavy wiring to the professionals. IMO the money you save isn’t worth the risk of a DIY mistake.

  14. #14
    Join Date
    Feb 2014
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    Lake Gaston, Henrico, NC
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    My large roll of wire is going to weigh 600 pounds, not even thinking about the dollars. I'm going to have to fab something to handle it with the loader.

  15. #15
    I had a 40 to start with. Just a waste. Put the 100amp box in and do it once. I think my aluminum wire was rated for 95 amp...

    Im not sure how you will run your home shop. I ran wire for a 40 amp and immediately realized it wasn't enough.

    My shop was a side business and then a full time shop. My electric secondary heater pulls 30 amps... my bench was wired for 20 amp. A compressor was on it as well. Everytime I used the belt sander the compressor kicked on and blew the breaker. You want plenty of power...
    Last edited by jack duren; 10-30-2021 at 10:20 AM.

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