adding an outlet in garage

Old 11-02-02, 02:48 PM
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adding an outlet in garage

I've been looking for a good air compressor to use because I collect old cars and could really use air tools for some jobs. I have a lead on a 5 hp, 60 gallon air compressor with 125 psi.

The seller says it requires 230 electrical hookup. My electrical box is in my garage not far from where I would put the compressor, so I'm wondering how hard it will be to install an outlet to handle this load, or what it might cost to have someone do it...

The electrical box is 50 years old and uses screw in fuses, but there is room to add more, if that makes any difference.
Old 11-02-02, 03:19 PM
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It's probably pretty easy. Not sure what it would cost in your area.
Old 11-02-02, 05:34 PM
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Do you have 240 volt outlets elsewhere in the house?

The reason I ask is I think it's possible that a house that old and a panel with screw-in fuses my not have 240 volt service entrance cables from the power pole to the service entrance main panel and the whole house may only be wired for 120 volts.

You can tell by looking in the main panel. If you have two heavy wires coming in from the service entrance to the fuse terminals and a heavy white wire going to the neutral bus, then you have a 240 volt service.

You can also look at the service entrance wires coming from the pole to the house. If there are two heavy insulated wires and a heavy stranded wire, you have 240.

If you have only one hot wire and one neutral in either case, then you only have a 120 volt service. To install a 240 outlet, you must have 240 service coming into the house.

If you do have 240, then it's a fairly simple proposition to add an outlet near the panel -- IF you have at least one open fuse slot on EACH leg of the hot bus bar. You CANNOT run 240 from only one leg of the bus bar -- it MUST come from both bars, so that 120 comes from one and 120 comes from the other.

You would run a 12 AWG black wire from each of those terminals to where you want the outlet and protect them with a 20-amp fuse in each.

You'd also need to run a green insulated or bare ground wire from the ground bar in the panel to the ground terminal in the outlet.

The outlet you'd need would depend on what kind of plug comes from the compressor, but should be rated at no less than 20 amps and 120/240 volts.

At the outlet, you'd wire the two black hot wires to each terminal and the ground wire to the ground terminal.

For wire, you should use 12-2 w/ ground NM-B (Romex) cable. You'd use both the black and white wires for the hots, but you'd need to wrap black tape around the white wire in several visible locations so anyone else working on the outlet would know that was a hot wire.

But BEFORE YOU DO ANY OF THIS you must pull the large cartridge fuses which are the main breakers that shut off power to the panel.

All this material should cost considerably less than $20 and I have no idea what an electrician would charge to do it for you.

However, if you have any hesitation whatsoever about doing it yourself you'd be well advised to hire an electrician. Whatever he charges will be quite reasonable compared to your electrocuting yourself or burning your house down.

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