220 Neutral/Ground Connection

[dwall174]

I have an old Marquette arc welder with a 3 prong 50 amp cord that needs to be replaced! The current wiring has the two hot leads connected to the switch & the ground wire connected to the main transformer's frame.

The welder has fiberglass side panels with a top cover & bottom frame made out of metal. The top cover & bottom frame are constructed so that the fiberglass isolates them from the inner transformer's frame.

My garage is wired with a 4 wire feed so I would like to replace the cord with a 4 prong plug which will give me a neutral wire that I can use to power a small 120 volt cooling fan.

Being that the fiberglass side panels isolate the top cover & bottom frame, Am I correct in figuring that the neutral wire will go to the transformer's frame & the ground wire will be connected to the metal top & bottom?

Thanks Doug

 

[larry_g]

You will have to keep the neutral isolated from the metal frame of the machine. Attach an isolated terminal strip in the machine and run the neutral wire to it as well as the neutral side of the fan.

lg
no neat sig line

 

[dwall174]

You will have to keep the neutral isolated from the metal frame of the machine.

Yea the frame that the transformer is mounted to is insulated from the metal bottom plate & top cover. The white neutral wire will go to transformer's frame & the green machine ground will be attached to the top cover & bottom plate/roller-base.

Attach an isolated terminal strip in the machine and run the neutral wire to it as well as the neutral side of the fan.

I was planning to add a small terminal strip for the neutral, But being the transformer's frame is isolated from the outer frame & top. I planned to just connect the neutral terminal strip to the transformer's frame.

Thanks Doug

 

[larry_g]

The only place the white neutral wire can connect electrically is to the fan. It has to be isolated from all other metal in the welder.

lg
no neat sig line

 

[dwall174]

The only place the white neutral wire can connect electrically is to the fan. It has to be isolated from all other metal in the welder.

Well that's where I'm sort of confused! The green ground wire on the original 3 prong 3 wire power cable was connected to the transformer's frame? The red & black wires were connected to opposite sides of the 2 pole power switch.

If I connected the new 4 prong 4 wire cable up the same way attaching the green ground wire to the transformer's frame & the white wire to a isolated terminal or just a fan, It would not be providing me with both a Neutral/Ground & a Machine or Safety ground.

I though the main reason for going from a 3 wire to a 4 wire hook-up (other than a neutral wire for 120 volt control circuit) was to provide both a neutral/ground for the motor (welder in my case) & a machine or safety ground for the cabinet of the machine?

Thanks Doug

 

[nehog]

Well that's where I'm sort of confused! The green ground wire on the original 3 prong 3 wire power cable was connected to the transformer's frame? The red & black wires were connected to opposite sides of the 2 pole power switch.

That's the way it is supposed to be. The transformer's core must be grounded.

If I connected the new 4 prong 4 wire cable up the same way attaching the green ground wire to the transformer's frame & the white wire to a isolated terminal or just a fan, It would not be providing me with both a Neutral/Ground & a Machine or Safety ground.

I see no reason to rewire the unit. You can't make it safer. If the unit currently does not use the neutral wire, there is no reason to run it. If you do run it, there is nothing to connect it to. Neutral is a current carrying conductor, it is not a ground conductor. Neutral has nothing to do with safety.

I though the main reason for going from a 3 wire to a 4 wire hook-up (other than a neutral wire for 120 volt control circuit) was to provide both a neutral/ground for the motor (welder in my case) & a machine or safety ground for the cabinet of the machine?

You need to stop confusing neutral and ground. Not the same animal, not the same purpose. Want to make it safer? Only one 'fix' might be to connect the cabinet metal to the ground in addition to the transformer's core, however I do NOT recommend doing this. There should be no possible leakage path between the primary circuit (the 240 feed) electrical parts that those panel pieces.

Question: you are not experiencing any symptoms of electrical leakage, are you? IOW, what prompted you to start down this path?

Please see my comments in your message.

 

[justsam]

As stated, your newly introduced neutral will only go to one side of your newly installed fan and isolated from any transformer frame, cabinet, etc.

Why is the fan being added? Welders are designed to operate within their spec'ed duty cycle, and dissipate heat as required

 

[larry_g]

Question: you are not experiencing any symptoms of electrical leakage, are you? IOW, what prompted you to start down this path?

From the first post;

My garage is wired with a 4 wire feed so I would like to replace the cord with a 4 prong plug which will give me a neutral wire that I can use to power a small 120 volt cooling fan.

Nehog has also explained about the neutral being a current carrying conductor and earth ground is a safety thing.

lg
no neat sig line

 

[dwall174]

The green ground wire on the original 3 prong 3 wire power cable was connected to the transformer's frame? The red & black wires were connected to opposite sides of the 2 pole power switch.

That's the way it is supposed to be. The transformer's core must be grounded.

Thanks that cleared up things a little for me!

I see no reason to rewire the unit. You can't make it safer. If the unit currently does not use the neutral wire, there is no reason to run it.

The main reason for replacing the plug & cable is because of it's condition! The welder is from the 60's & the original power cord is worn & it's insulation is starting to crack.

Question: you are not experiencing any symptoms of electrical leakage, are you? IOW, what prompted you to start down this path?

No other problems except for needing to replace the old worn out cord!
Just over thinking things I guess!

Thanks Doug

 

[dwall174]

As stated, your newly introduced neutral will only go to one side of your newly installed fan and isolated from any transformer frame, cabinet, etc.

Yea nehog help clear that up for me!

Why is the fan being added? Welders are designed to operate within their spec'ed duty cycle, and dissipate heat as required

Just thought it may help out a bit to keep things a little cooler & it wouldn't be hard to add one since I had to removed the top & side panel to get at the wiring.

Doug

 

[rockwithjason]

why not use a 240v fan?

 

[Stuart in MN]

why not use a 240v fan?

Perhaps something like this would work: http://www.ebay.com/itm/220V-230V-240-V-AC-Cooling-Fan-120mm-x-38mm-/330534508513