Setting up a 220v service in the garage.

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I would like to install a 220V service in my garage.
Mostly to, first, sometimes warm it up during winter weather when I need to work on something, and second, I want 220V there for testing various military surplus equipment that I sell. I have a 220V generator, but it is a pain to wheel it to the garage. I feel that the better solution is to install a proper 220V circuit.
I have some space lift in my panel.
Please criticize my plan:
1. Install a double 20A breaker for 220V. 2. Use 10 gauge wires 3. Use rigid conduit (EMT). 4. Install a 20A double plug 220V receptacle.
Would this be sensible?
--
223/172.3/180

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Ignoramus32046 wrote:

Is this an attached garage or detached? If it's detached, is there already a 120V circuit running out there for a light?
A building can only have one electrical service. This is not an issue if it's an attached garage.
Bob
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I did not know that. Reason?
Is it allowed to run the 220 circuit to a subpanel and break it down to a couple of 110 also? Then abandon the original circuit so you still only have one.
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Edwin Pawlowski wrote:

I assume it is so there is a single point (the service entrance disconnect) where all the electricity can be shut off for the building.

Yes. I'd run at least a 40A service with #8 wires. 100A main lug load centers with 6 or 8 spaces are Very Cheap and are suitable for service equipment. You could feed it with whatever size feeder you want -- up to 100A, of course. Eight gauge wire is particularly easy to work with because it is fine-stranded.
Then abandon the original circuit so you still only have one.
Yes.
Best regards, Bob
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it is attached, part of the house.
i

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Ignoramus32046 wrote:

Then you can run a new circuit with little regard what's already there.
What you are proposing is fine; you might consider using NM cable ("romex"), and if the run is not too long maybe #12 instead of #10.
Best regards, Bob
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Do you mean romex without metallic conduit? That would certainly save me a lot of time. I would rather use oversize cable than undersized, that's so because I will test some rather serious equipment. (I already did, in a cludgy way with generators)
In fact, I am considering change in plans and run a #8 AWG cable and a 30 amp service. Can I have a 20A and 30A outlets on one box, on a 30A circuit?
I figure, for a small difference in cost, with the same investment of time, I can end up with a badass power in the garage, instead of quite marginal 20A 220V.
If I am not required to use metallic insulation, I can definitely do it all in one day!
i
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Ignoramus32046 wrote:

You can't mix 20A and 30A outlets on the same circuit.
You can run a 30A circuit using a dryer outlet, and make a short adapter cord to get your 20A outlets. Doesn't military equipment use twistlok power connectors, and other weird stuff? ( so you might need adapters anyway.)
Bob
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okay.

They often have no connector at all. I can have a dryer outlet and a adaptor, as you suggested. I am surprised that I cannot mix such outlets, there seems to be no harm in that, as long as the circuit is good enough for the biggest outlet.
i
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Using adapters off of over sized outlets is poor practice at best. The entire purpose of Over Current Protective Devices (OCPDs) is to limit the current to amounts that the circuit AND THE CONNECTED LOADS can carry. If a piece of equipment you are testing is jammed it will draw a very high current that is called the "locked rotor current." The overload protective device associated with the motor should open in time to protect the equipments wiring from disastrous and destructive heating but if it does not the size of the OCPD that protects the circuit that supplies the outlet is the only remaining defense against an equipment burn down. The US NEC specifically forbids connecting undersized outlets to circuits. The schedule of outlet ratings and circuit sizes is laid out in Table 210.21(B)(3). -- Tom H
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Thank you for your well informed opinion. Just today I blew circuit breakers in the garage and kitchen due to running some stuff like a heater and a compressor. I think that I will splurge and install a real subpanel in the garage, and then a few outlets, 110 and 220v. This subpanel should also be protected by circuit breaker at the main panel, is that right?
i
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Ignoramus14233 wrote:

that protects the feeder circuit that supplies it fulfills that function. -- Tom H
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Yes and no. No in that the breaker at the main panel protects the cable(s) running to the sub panel, not the panel, or its circuits, but just that cable run feeding it.
Yes, in that it will have the effect of a shut off for the sub panel, but that isn't its intent.
You don't need a breaker that shuts off the whole sub-panel, in addition, you can have only the breakers you need for circuits.
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It is really the issue of providing the proper overcurrent protection for the smallest connector.
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The only code compliant way to use the same circuit to supply both twenty and thirty ampere loads is to run a feeder that supplies Over Current Protective Devices (OCPDs) that will protect the different size circuits. The easiest way to do that is to run a feeder to a sub panel in the garage. You need to figure out what is the largest sum of the loads that you would want to run simultaneously and would any of those loads need to run for more than three hours at a stretch. If the equipment you are testing is electric motor driven then you take 1.25 times the largest motor load plus all of the remaining load to get the ampacity of the feeder that you will need to supply those loads. Any load that will run for more than three hours at a time should also be multiplied by 1.25 before adding it to the other loads. -- Tom H
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Thanks. I think that I will provide a single 30A outlet, and also will buy an extra dryer cord and add a 20A outlet to its end. I have no idea what will be the electrical equipment to be connected to this circuit, so I want to have a lot of capacity.
i
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Ignoramus14233 wrote:

It won't cost that much to run your thirty ampere circuit to a small six slot sub panel with three double pole breakers for a thirty, twenty, and fifteen ampere outlets. Limiting the supplied current to what the device under test should run on may well prevent a lot of additional damage if the unit being tested fails the smoke test when you first energize it. -- Tom H
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They make surface mount fuse holders, for screw in fuses. You could use one to protect a sub service, or for individual device protection. Then the 15 amp outlet could be protected at that level.
In your case, a small sub panel would work, allowing a mix of circuits as needed.
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Yep, like you and Tom are suggesting, I will install a subpanel.
i
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zxcvbob wrote:

An additional branch circuit as in this case would not be considered a service.
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