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Thread: How many amps should my sub panel be? & should I get a gas line for heat?

  1. #1
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    How many amps should my sub panel be? & should I get a gas line for heat?

    We are building a new house.
    It will have a three car garage.
    The third bay will be my shop.

    The house will have 200 amp service.

    I'm going to have them run a sub panel - I now have a 30 amp sub panel & it is a bit small, so, I plan on at least 50 amp.
    Should I or can I go up to 100 amp?

    My wife also suggested that I have them run a gas line so I can put in a gas space heater. Good idea or not?
    My granddad always said, :As one door closes, another opens".
    Wonderful man, terrible cabinet maker...

  2. #2
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    You should calculate the maximum power consumption that will be needed at the same time from that panel and then add 20% or so. You can run 100 amps and if it were me that is what I would do even if I don't necessarily need it. Two tools, say a vacuum and a table saw, may draw 40 amps or more at start up. But seldom are machines started at the exact same time. Consider AC and maybe electric heat (mini-split heat pump perhaps) and all other things that might be running in that space: air compressors, fans/blowers, frig, microwave/toaster oven, computers, TVs, music, charging stations, aux lights. I think you'll find 50A might be marginal. If your tools are on the lower HP end, then 50A might be OK.

    Gas heat is excellent: warm and fast, but doesn't provide any cooling (at least not efficiently). Gas used to be cheap. Seems to be less so these days.

    Would you ever consider an electric car? If so then charging for that should be considered while your at it.

  3. #3
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    Go for a 100 amp sub-panel The added cost is minimal.

    Agree with Tom. Look at a mini-split for heat and cooling. That's what I did in my garage shop.
    ===========

    James Cheever
    Ga Tech NROTC - 1978
    Run Silent, Run Deep
    Commander, USN (Retired)

  4. #4
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    upsizing is a whole lot cheaper now than later. Tom has a good point about a potential electric vehicle or a welder. A stick arc welder (Lincoln Electric 225 amp 'buzz box')requires around a 50 amp circuit.

  5. #5
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    I put in a 100 A subpanel and now find it is too small. I put in a RPC on a 60 A breaker to make three phase power for my jointer/planer and now the lights go dim if I turn it on with anything else running. Do a load calculation for everything you think might possibly run at once-- compressor, dust collector, air conditioner, and the biggest machine you hope to have and then go at least 20% over that-- I'd double that number myself.

    The cost difference in going bigger on a subpanel is typically not very much; primarily just the cost of the wire.

  6. #6
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    Quote Originally Posted by James Cheever View Post
    Go for a 100 amp sub-panel The added cost is minimal.

    Agree with Tom. Look at a mini-split for heat and cooling. That's what I did in my garage shop.

    +1

    ...........

  7. #7
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    The cost difference between a smaller sub and a 100 amp sub is pretty minimal. The breaker is a little more and, of course, the feeder wire is what it is, but in the long run, you'll forget about that. I did a 100 amp sub for my temporary shop even though the planned needs were lower. It was just simpler to do it that way.
    --

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

  8. #8
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    Is your shop (the third bay) walled off from the rest of the garage? If it is not, you'd be heating or cooling the entire garage. That's maybe not such a good idea. At any rate, you should insulate the walls and ceiling anywhere you're going to heat.

  9. #9
    New construction? 100A for sure. I would also run the gas line. It gives you options going forward. A mini-split is the way i would go. I H/C the house with them and am considering adding one to the shop, but right now I have just gas heat in the shop. As this is new construction look to adding solar on the building or at least orienting to accept it for future. You say the third bay will be your shop area. Will that be walled off or the entire space open?

  10. #10
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    I had planned to put up a wall between the 3rd bay and the rest of the garage.

    As far as electric vehicles go, I have no plans to get one - but - at some point in this house's future, that's probably the only way vehicles will come & 120V charging just won't get it done so - some sort of 220V line will have to be run.
    Might as well get that in place from the beginning I guess.

    It looks like the 100amp panel is the way to go.
    My granddad always said, :As one door closes, another opens".
    Wonderful man, terrible cabinet maker...

  11. #11
    I would do the 100 am panel as well. If your house is still under construction, I would look a radiant in floor heating, I think it will be more efficient than any gas fired heater. If you do wall off the bay a mini split should heat and cool fine.

  12. #12
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    If you really need 100 in the shop, I'd more concerned about the 200 in the main panel.
    The Plane Anarchist

  13. #13
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    While the walls are open I'd pull a 100 A circuit for the shop and run a separate 240V 60 A circuit from the main panel for a dedicated car charger (2 x #6 AWG copper plus #10 ground), or pull the neutral and install an outlet instead. The charger doesn't need the neutral, but at least in MA they won't let you install a NEMA 14-50 or 15-60 outlet without it in a house; the hard-wired charger doesn't require the neutral or an additional GFCI breaker. Or at the very least run conduit and leave a pull string to add the charging wire. If you're quick you can get 35% of the cost of installing a charger back on your taxes if you do it before year-end. Lots of places code now requires pre-wiring for a charger in new construction, you are probably going to want it in the future, your next buyer will certainly want it.

    Depending on the rest of your loads I'd consider a bigger main panel.

    A 60 A circuit, which allows 48A car charging, is probably adequate for the foreseeable future, allowing a charge rate of about 45 miles added per hour, plenty for overnight charging at home.

  14. #14
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    Quote Originally Posted by Rich Engelhardt View Post
    I had planned to put up a wall between the 3rd bay and the rest of the garage.

    As far as electric vehicles go, I have no plans to get one - but - at some point in this house's future, that's probably the only way vehicles will come & 120V charging just won't get it done so - some sort of 220V line will have to be run.
    Might as well get that in place from the beginning I guess.

    It looks like the 100amp panel is the way to go.
    You may be able to get some tax advantage by putting in 240v to the garage to be able to support EV charging. Doing it with a subpanel is a perfectly reasonable accommodation for that. That further supports the idea of a 100 amp sub, too. For your purposes, even if you were to acquire an EV or two in the future, the charging would generally be complimentary to the machinery use because those two things would typically occur at opposite time frames.
    --

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

  15. #15
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    Quote Originally Posted by Rich Engelhardt View Post
    I had planned to put up a wall between the 3rd bay and the rest of the garage.

    As far as electric vehicles go, I have no plans to get one - but - at some point in this house's future, that's probably the only way vehicles will come & 120V charging just won't get it done so - some sort of 220V line will have to be run.
    Might as well get that in place from the beginning I guess.

    It looks like the 100amp panel is the way to go.
    My son is building. He has two hybrid vehicles. He has two kids... so he anticipates a third electric vehicle.
    He will have a shop. Electric range, dryer, a/c. It seems likely that all of these will be running at the same time in some cases.
    He was speced at 320 amps for the main service, but was told 400 amps could be run for the same price.

    With the 2020 NEC of an exterior disconnect, his set-up is:
    - 400 amp exterior main/with disconnect,
    - 200 amp sub for the house proper
    - 150 amp sub (or 125, can't recall) for the garage (for three chargers at 40 amps 240 volts each, plus regular 120 volt circuits.
    - 100 amp sub for the shop
    - 60 amp sub for a possible hot tub on the deck.

    If you are sharing the sub in the garage for a shop and possible electric chargers I would expect 100 amps to be a given, and might look at 150 or 125 as possibilities.

    Edit: with the increased focus on electric vehicles and both he and wife working a lot from home, a steady supply of electricity is necessary. Iowa has had increased severe weather related outages lately. To that end, he is also rigging his electric layout to be run by generator if need be. I believe it is an automatic transfer switch incorporated into his electric meter.
    Last edited by Charlie Velasquez; 12-30-2021 at 11:54 AM.
    Comments made here are my own and, according to my children, do not reflect the opinions of any other person... anywhere, anytime.

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