Wiring 240v receptacle for Hammer A3-31

[Charles Goodwin]

I have a new Hammer combo j/p that's sitting in my shop, smiling at me, wondering why we can't have some fun together. The problem is that I need a 240v receptacle appropriate to the machine, and while I'm fair with standard household electric work I get lost at the jump to 240. But I can follow instructions, so am hoping someone here can walk me through it.

The Hammer comes with a short cord with three wires - a blue, a brown, and a yellow/green. No plug. About all that the instructions say is that a 30a breaker is required, the yellow/green is the ground, and the blue and brown are the "phases."

I take it that means that I need a three-prong rather than a four-prong 240 outlet. So the first question is if it's acceptable under the current NEC to have a three-prong 240 outlet? I've read some discussion that the NEC now requires four-wire connections.

Second question: If three-prong is what I want, is the following correct: (1) install a double-pole 30a breaker in my subpanel; (2) run 10-2 wire to the receptacle; (3) use both the black and white wires as hots (marking the white accordingly) and connect each to a pole on the breaker; (4) connect the ground wire to the equipment ground in the subpanel; (5) at the receptacle, connect the two hot wires to the two brass screws; (6) at the receptacle, connect the ground wire to the ground screw. This seems off to me (two hots but no neutral?), but maybe I just don't get it.

Third question: My subpanel, being in a detached building, has the ground bus isolated from the neutral bus. Does this affect the wiring in any way?

Thanks,
Charles

[Stephen Cherry]

It sounds like you've put some thought into this. You might be right about the 4 wire supply. I have a felder saw though, and it seemed like the wiring was very well done. If you have a control transformer which produces the juice for the contactor using both legs of the 220, for example 220 vac to 24 vac, you are fine. Where you need the neutral wire is where the control power for the contactor, lights, etc, is 120 vac, returning current on the ground wire. I guess this used to be fine, but now is a no-no.

The short answer, look at the wiring diagram of the machine, and make sure that the juice for the miscellaneous stuff is derived from a transformer and nothing is using only one leg of the 220 volt supply, then there is no need for the neutral.

[Glen Butler]

If the hammer only has the wires then there is nowhere to run a fourth "neutral" wire to the machine. So as you thought, you should only need a 10-2 w/ ground -- two hots coming from a two pole breaker and going to each hot leg of the machine. (but checking a wiring diagram couldn't hurt)

[Josiah Bartlett]

If you have to pull wire and it is going to be hard to retrofit later, it would be a good idea to pull 10/3 with ground to the box, so if you change over to a machine that requires a neutral, you have it. However, if it is going to be easy to service the wire later or you don't think you will upgrade the machine, 10/2 is cheaper. The majority of 240V tools I have use 10/2.

[Nathan Dekens]

Yes in order to run your machine at 220VAC you need 2 hots and a ground. The 4 prong issue you are refering to in the NEC is to cover electric dryers. They want you to run a neutral because the dryer runs on 120VAC control power and only uses the 220 vac for the heating element. The 120 vac portion will return through the neutral and not the ground wire.

Run 10/2 and install a 30 amp breaker. Do not wire this to a standard 120 vac house plug as they are not rated for 30 amps and could cause confusion should someone un-knowingly plug in a 120 vac device.

I would use a receptacle like this:

http://www.homedepot.com/Electrical-Outlets-Plugs-Outlets/h_d1/N-5yc1vZ1xgtZbp9i/R-100121426/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053

And a plug like this:

http://www.homedepot.com/Electrical-Outlets-Plugs-Plugs-Connectors/h_d1/N-5yc1vZ1xgtZbodr/R-100114938/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053

[Chris Padilla]

Yes in order to run your machine at 220VAC you need 2 hots and a ground. The 4 prong issue you are refering to in the NEC is to cover electric dryers. They want you to run a neutral because the dryer runs on 120VAC control power and only uses the 220 vac for the heating element. The 120 vac portion will return through the neutral and not the ground wire.

Just to add a touch more there, Nathan, the ground wire is there for safety only. With 240 V, there is no neutral for current to flow through so they flow/return through each other...but certainly not the ground wire unless there is a problem somewhere. :)

[Nathan Dekens]

Just to add a touch more there, Nathan, the ground wire is there for safety only. With 240 V, there is no neutral for current to flow through so they flow/return through each other...but certainly not the ground wire unless there is a problem somewhere. :)

Thats what I meant to say........

[David Helm]

Since nobody answered your question about the isolated grounds and neutrals at your sub panel I guess I will jump in. Your subpanel is wired correctly, grounds and neutrals isolated (they are only bonded at the main panel). It will have no effect on the wiring of your outlet.

[Charles Goodwin]

Thanks - wired up and running!

[bradley lewis]

Old post I know but it's relevant...

My shop already has L14-30 receptacle's installed. Can I use a matching plug and just omit the 4th "neutral" wire?