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?
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.
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.
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.
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
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!
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
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.
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).
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?
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.
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.
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.
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
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
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