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Thread: Sizing of electrical sub panel for garage/shop

  1. #1

    Sizing of electrical sub panel for garage/shop

    It started so simply by buying a 5hp OMGA RN900 RAS, actually 230v 3 phase but with a brand new 230v 1 phase motor in a box. You don't even want to know what the previous owner paid OMGA for a new motor!

    Time to install a sub panel and I want to do it right the first time. I can see having a number of tools that draw power but can't see running too many at the same time - Dust Collector and a couple tools at once, probably mostly one at a time. I have lots of experience with big equipment from business but all of the wire gets bigger as the voltage drops from 460v to 230v or 120v and goes to single phase. I'll probably need lots of AC in my area. Lots of light also but much of my lighting is 120-277v so I may run it on 230v also.

    What did you end up with input power on your sub panel and how much you running for 1-2 people working at once? What would you do differently?

  2. #2
    Join Date
    May 2007
    Kansas City, Missouri
    I've got a 100 amp off the 200 amp main. I dont use a lot at once, but its there if i need it.

    Sent from my SM-G920P using Tapatalk

    To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault

  3. #3
    Join Date
    Jul 2011
    The Gorge Area, Oregon

    Start adding up the pieces and figure in your surge requirements. I think at a minimum you should plan on the AC, DC, lights and compressor plus the worst machine(s) all running at once (say the worst 2 machines for planning).

    Luckily my main panel was in the garage/shop and I was able to wiggle enough room in it to hookup everything I needed (with no space to spare). If I was doing it from scratch and didn't have any "crazy" machines (like a widebelt which also kicks the DC requirements through the roof or something like my cousins 50hp sawmill he runs off of a rotary converter) and was still just 1-2 machines (over the dc+ac+comp+lights) I can't see easily exceeding 240v/100a even with surge demand. Even the sawmill fit in 240v/200a (the dust collection on it is a bobcat and a shovel of course).

    Lighting shouldn't be a huge draw, if it is imho its time to look at better lighting solutions (t8's only take ~35w per on the high side, smaller fixtures are closer to 10-20w LED is in the same or better ballpark - either way that's fractional amps per fixture). The lighting draw should be roughly the same 240v vs 120v although you can drop wire gauge so that can be nice.

    Having sufficient slots in the panel can be nice for running dedicated circuits though - so my preference is 200a panel with a 100a main breaker just for the breaker slots. It costs a bit more but running out of slots is a pain.

    Sounds like someone is doing a fun shop upgrade anyway

  4. #4
    Join Date
    May 2007
    Thomasville, GA
    I had a 100A subpanel installed in my shop. It has 30 breaker positions and has a total of over 300A of breaker capacity. In reality, if I add up all of the things that could possibly be on at the same time, total draw is about 67A.
    Bill Arnold
    Citizen of Texas residing in Georgia.
    NRA Life Member and Member of Mensa
    My Weather Underground station

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