Wiring a 240v outlet


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Old 03-13-06, 01:29 PM
C
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Question Wiring a 240v outlet

I am swapping out a 4-prong 220v outlet for a 3-prong one, and need to know what to do witht the white and green wires. I Know the red and black arrangement as they were clearly marked on the 4 and 3 prong outlets, but the white line is where I don't want to make the mistake. Being as it should be the "return leg" can I wire it with the ground (green wire) or do I cap it off. The electricitian that installed the 4-prong outlet did not know that the machine was already plugged for 3-prong.

Sorry for the confusion:
I have a 220V radial arm saw that I am trying to get plugged in safely. The architect and contractor that my (non-profit) organization used did not care what I actually needed they did it all on spec(-ulation). They had the electrictian wire in a 4-prong outlet, and the machine was on a 3-prong twist-lock outlet. I was able to salvage the old outlet before the shop was relocated and I was hoping that I could fix the issue myself.
 

Last edited by Chris Mc; 03-14-06 at 07:46 AM.
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Old 03-13-06, 01:38 PM
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For a four-hole receptacle with a four-wire circuit, red and black go to "X" and "Y". White goes to "W". Ground goes to "G". The shape of the slots depend on whether you're talking about a 30-amp or 50-amp receptacle.

At the beginning of your post, it sounded like you were removing a 3-hole receptacle and adding a 4-hole receptacle. But at the end of the post, it sounded like the reverse.

If you have a house with a 4-hole receptacle, and a range or dryer with a 3-prong plug, you are required to change the appliance cord and plug to match the receptacle. You are not allowed to change the receptacle to match the cord and plug. When changing a cord and plug, it is absolutely essential to carefully follow the manufacturer's instructions. A bonding strap on the appliance must be removed.

If this is for a welder, then things are different.

Please post back with more information about what you are doing and why.
 
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Old 03-13-06, 04:13 PM
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. . . . . .
 

Last edited by bolide; 03-14-06 at 02:04 PM.
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Old 03-14-06, 07:43 AM
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Unhappy Sorry for the confusion

I have a 220V radial arm saw that I am tryingto get plugged in safely. The architect and contractor that my (non-profit) organization used did not care what I actually needed they did it all on spec(-ulation). They had the electrictian wire in a 4-prong outlet, and the machine was on a 3-prong twist-lock outlet. I was able to salvage the old outlet before the shop was relocated and I was hoping that I could fix the issue myself.
 
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Old 03-14-06, 08:49 AM
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This is in the garage, or a shop, right? This is not a receptacle that was previously meant for a home appliance? If this is correct, then you have no Code violation.

You can replace the receptacle, leaving the white wire capped and in the back of the box for a future use.

Use the green or bare wire as the equipment grounding conductor, and the two hots, as you suspected.
 
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Old 03-14-06, 09:23 AM
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I agree. Now that we have all the details, we know that what you are doing is fine. Follow Mac's advice. Be sure to verify that the amperage rating of the circuit matches that specified by the saw manufacturer.
 
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Old 03-14-06, 10:02 AM
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I would suggest a small modification to the above instructions.

If the saw is in fact a pure 240V device, then proceed as above. However with old machine tools sometimes corners will have been cut. In particular, small incidental loads such as control relays or lights may be run at 120V between one of the hot legs and the frame ground of the machine.

I would suggest that you investigate the wiring of the machine to confirm that this is not the case, and that the machine is a pure 240V load. If the thing is just a motor with control switch connected to the 240V supply, then you are fine. Be wary of any lights or blowers on the machine.

If the machine has 120V loads, then I would suggest that you change the cord on the machine to match the four wire receptacle.

-Jon
 
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Old 03-14-06, 11:37 AM
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Thank you all for your help

This relocation has been all about making do, with the shop and the tools that we have.
 
 

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