[Dave2024]

So I'm preparing to convert a machine of mine from 120 to run on 220. The 120 I noticed while probing with my multimeter reads 120v when contacting the neutral and hot wires. When I prob across the neutral and hot wire on the 220 I'm reading 220. On the 120 when probing either neutral or hot with the ground I don't get a reading. But when probing either the neutral or hot on the 220 I get 120. It there going to be a malfunction or some kind when I got to turn the machine on for the first time if the ground is making 120? The machine says its rated for 120~220v and so dose the transformer in its panel. Should I reconsider attempting this and go to school to become a lineman first or is this just one of those hurdles in never doing this before? Thanks

Or also should I just run the two hot wires of 220 and have no ground?

[RaderSidetrack]

When I prob across the neutral and hot wire on the 220 I'm reading 220.

What country are you in?


If you are in the USA or Canada, 240 volts from the structure's breaker box is going to come from 2 hot wires when the electrical service is single phase. Normally residential and small commercial service is single phase. Hot to neutral should be roughly 120 volts, if its not, you may be misunderstanding what you see. If you really have 3 phase hire an electrician.

You should clarify this issue before going any further.

[Dave2024]

What country are you in?


If you are in the USA or Canada, 240 volts from the structure's breaker box is going to come from 2 hot wires when the electrical service is single phase. Normally residential and small commercial service is single phase. Hot to neutral should be roughly 120 volts, if its not, you may be misunderstanding what you see. If you really have 3 phase hire an electrician.

You should clarify this issue before going any further.

Ok so yea I guess you could say the two hot wires of the 220 are reading 220 and then if I take a reading of the ground and one of the 220's hots it reads 120. So when I connect the 220 to the machine only use the two hots and leave the ground disconnected? Basically only 2 wires connected to the machine supplying the 220? Or should I also connect the ground wire. I included a page out of the machines manual maybe you could look at. I suppose its single phase so just the two hot wires need to be connected? Thanks

[RaderSidetrack]

The "ground" wire is not the same wire as the "neutral" wire. In a 120VAC device there is a hot wire and a neutral wire. Both of those are current carrying conductors. There SHOULD also be a "ground" wire, which does not carry a current but is there for safety reasons. There may be a dedicated screw on a terminal block for "ground", or it could be just connected to the machine frame.

When you convert the machine to 240VAC, you have two different hot wires, but the ground connection remains the same as it was in the 120VAC scenario.

If you do the conversion by changing the power cord "plug", what was previously the neutral wire typically gets repurposed to become the 2nd hot wire. If the machine doesn't have a plug and is connected directly, similarly what was previously the neutral wire typically gets repurposed to become the 2nd hot wire by moving the wire connection.

The ground wire should remain undisturbed. In the case of your isolation transformer, if you don't have dedicated ground terminal already, one of the transformer mounting bolt (holes visible in the bottom foreground of the photo) could serve as a ground connection -- assuming the transformer is mounted to part of the machine steel/metal frame.

[Dave2024]

The "ground" wire is not the same wire as the "neutral" wire. In a 120VAC device there is a hot wire and a neutral wire. Both of those are current carrying conductors. There SHOULD also be a "ground" wire, which does not carry a current but is there for safety reasons. There may be a dedicated screw on a terminal block for "ground", or it could be just connected to the machine frame.

When you convert the machine to 240VAC, you have two different hot wires, but the ground connection remains the same as it was in the 120VAC scenario.

If you do the conversion by changing the power cord "plug", what was previously the neutral wire typically gets repurposed to become the 2nd hot wire. If the machine doesn't have a plug and is connected directly, similarly what was previously the neutral wire typically gets repurposed to become the 2nd hot wire by moving the wire connection.

The ground wire should remain undisturbed. In the case of your isolation transformer, if you don't have dedicated ground terminal already, one of the transformer mounting bolt (holes visible in the bottom foreground of the photo) could serve as a ground connection -- assuming the transformer is mounted to part of the machine steel/metal frame.

Ok so it should be ok to use the neutral wire on the 220 kind of like a ground wire? So go ahead and connect it to the ground bar in the machine? Then the two hot wires connect them to the 220 receptacles inside the cabinet? It should make it safer than only having the only the two hotwires incase there's a short and make the main breaker flip rather than trying to weld a hole through the cabinet?

Thanks for all the help on this btw. I really appreciate all the help and you make this very easy to understand

[RaderSidetrack]

I cannot recommend using the neutral wire as a ground. Its too easy to get confused when you look at it later, as neutral is normally a white color.

Lets start over: What you should have in a 120 volt machine is: black wire = hot, white = neutral, and green = ground. So when you convert to 240 volts use the existing black wire as hot(1), the existing neutral at hot(2) IF you want to reuse the neutral wire, and green = ground. If you are doing this I suggest using a paint pen to "paint" both ends of the former neutral wire insulation with red (or black) paint so there is a visual indication that that wire is no longer neutral, as it is now 'hot'.

If you are running new wire for the 240 volt setup, I suggest using colors of black = hot(1), red (or black) = hot(2), and green = ground. Bare copper wire is also an acceptable color for ground wire.

[Dave2024]

Ok thanks for all your help! Using a long stick safety glasses and a fire extinguisher and quick access to the main braker I flipped the switch for the first time. It was flawless. Its just single phase without a ground. I don't have a ground just the two hots and a neutral. I left the neutral disconnected and with a wire nut. Thanks for all your help and take care RaderSidetrack