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Discussion Starter #1
Rookie welder here, with a Millermatic 211. I just bought a Miller welding table, and the brief instructions with it say "if you wish to ground the table...".

I spent yesterday evening googling the subject, and there are a lot of strong opinions out there, on both sides.

I plan to use the welder with two power sources, depending on whether the work can be moved into my shop to the table or not. In the shop, there is a dedicated welder outlet with its own 240V electrical circuit from the barn sub-panel. The second power source for outside is a Honda portable generator, which is floating ground.

My question really related to the table, but if there are any recommendations about the generator I'd appreciate those as well.

Thanks.
 

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I ground my table, but, I do not care if an arc occurs on the surface,

The best approach would be to ground the table, then have an auxiliary ground wire/clamp from the table to the part being welded.
 

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Just to be clear, are we talking about an "earth" ground or the ground lead from the welder?
 

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At my place of employment I ended up isolating any possible path to ground that could result from the welder power supply. I individually installed a ground rod for each welding table.
 

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Discussion Starter #5
Just to be clear, are we talking about an "earth" ground or the ground lead from the welder?
A ground to earth, like a connection between the metal of the table and a ground rod. Separate from the clamp from the welder to the piece being welded.

I'm assuming the welder itself is grounded to earth via the elctrical outlet?

So, a ground between the table and earth would protect me from my body beicoming the path to ground?

What makes this difficult for me to understand is watching folks weld on cars. Unless they use a ground to earth from the car that I am missing somehow?
 

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I agree 110%. I would NOT want any welding current finding a path into the building's electrical system through a fault in the welder's secondary circuit in any way shape or form.
:hornets:
 

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Discussion Starter #7
Thanks for the input so far. Now I'm thinking about a way to ground the table to earth.

My shop has a concrete floor. A thought is to drill a hole in the concrete to the dirt below, and then to hammer down a grounding rod with a connection to the table. Now I need advice on that. What diameter rod? How deep? Should the road be insulated from contact with the concrete slab? What gauge wire to use between metal table and the ground rod? Or is this even a reasonable plan?

I've thought about hiring a licensed electrician, but the various opinions I see posted on the internet about this whole subject just shows me that among electricians there seems no consensus about what is right. I've never seen the magical NEC, but with so many interpretations of what it says out there I am really confused. Is the NEC really that ambiguous? What if I pick the wrong electrician?
 

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Thanks for the input so far. Now I'm thinking about a way to ground the table to earth.

My shop has a concrete floor. A thought is to drill a hole in the concrete to the dirt below, and then to hammer down a grounding rod with a connection to the table. Now I need advice on that. What diameter rod? How deep? Should the road be insulated from contact with the concrete slab? What gauge wire to use between metal table and the ground rod? Or is this even a reasonable plan?

I've thought about hiring a licensed electrician, but the various opinions I see posted on the internet about this whole subject just shows me that among electricians there seems no consensus about what is right. I've never seen the magical NEC, but with so many interpretations of what it says out there I am really confused. Is the NEC really that ambiguous? What if I pick the wrong electrician?

Unless water can get to that spot, the dry earth rod might be useless,,
my BIL's shop had a loose ground somewhere,, when the two ground rods outside the shop would dry up, you would get shocked,,,

We quickly learned, if it had not rained for a couple weeks, run the hose on the ground rods before using power tools,,
The rods were radically different with 5 gallons of water on them,,

(eventually, we found the loose ground,, a twist of a screw, and the shocking stopped)
 

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My father has been a professional welder for almost 50 years and we've never had a table grounded to a ground rod separate from the neutral going to the bus bar and I'm not aware of any specific NEC code that either reccomends or requires it. A 30 or 50 amp 220 circuit is an isolated circuit or it should be. Ill ask my pop what the industry gooroos say and edit my post.

Update

I had a discussion with my father, who retired from the biggest poultry and beefpackerr in the country, and he said none of their welding tables were grounded. He also said that OSHA frequented his shop regularly over his 40 plus years there and never made mention of it. I have no opinion either way. I'm just passing along info from someone knowlegable.
 

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The earth is a pretty crappy conductor, wet or otherwise.

What you want to do in this case anyway is to place the table at the same potential as the electrical service ground. Connecting the return clamp from the welder to the table should do this since it is bonded to the welder case which, in turn, is connected to the electrical service safety ground (green or bare wire). Of course, you run the risk of spot welding the work piece to the table in this situation.

You don't want a separate ground rod. You want to run your ground wire to the electrical service ground, which will be near the panel and will be bonded to a single ground rod nearby. Possibly to a copper pipe if your municipal water service is copper (I don't think this is allowed by code any longer, but was common up to the mid 80's).

FWIW, I've never given this a thought. I weld with a portable table and have yet to be shocked.

Cheapo buzz box welders produce maybe 80 volts with an open circuit. This may surprise you if shocked but should not be fatal unless maybe you have a serious heart condition where you shouldn't be welding anyway. Most halfway decent welders are in the vicinity of 40v maximum.

Bottom line, I cannot think of an electrical safety reason to ground the table. But I am willing to learn!

Al
 

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I have read this thread with some interest!!

Here is what i know. Service entrance grounding (e.g. ground rod connected to the ground terminal in the panel) really only comes into play if there is external current flow from sources such as lightening or a ground fault, usually in a motor.

If you are getting shocked by your electrical system due to the ground rod not making good contact with the ground, you potentially have an open neutral circuit. The neutral circuit cares the imbalance current that occurs between the two 120 V legs back to the transformer. If the neutral circuit is open or high in resistance, this imbalance current will try to find another way back to the transformer, which can be the ground rod.

Now to the welding table. The only reason I can think of for actually connecting your welding table to an earth ground is to prevent any possible shock that could occur if you touched the welding table while welding and the welding ground clamp wasn't connected properly. But, even then, i believe it would be possible for you to still get some shock. :dunno:

Grounding something isn't always a guarantee that you will not get shocked! We can still draw current.

The only reason a ground fault breaker prevents shock is because the breaker kicks the second the ground sees even a small amount of current.
 

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I can't think of a reason to ground a welding table, but I'm open to hearing the advantages.

The only thing that I can think of that it will do is allow you to weld the table itself (unless the welder has an isolated ground).
 

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For the life of me I don't understand why you would want to put an earth ground on a welding table. It is not a power source.
A bodily shock is only going to happen when your body provides a return path to the source through the ground you are standing on IF one side of that source is grounded also.
That's why you can touch one side of the welder's output terminals and not feel a thing because that current is only trying to get to the other terminal of the welder and as long as that other side isn't laying on the ground......you're safe.
That ground rod on your electrical panel isn't there for your safety, It's there to keep from burning the building down and trip a breaker should a fault occur in an appliance.
Shockingly :mocking: your generator is safer in that regard than your home's electrical system if it's sitting on an insulated surface.
 

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We had fluorescent fixture hung with light chain over the top of our welding tables. The cross brace they were suspended from was constructed with thin walled square tubing that was welded directly to the table. These lights were often plugged into those power outlets many folks use for computers and monitors and such.The guys may have small fans, radios or a rotating weld positioner along with the lights.
We were seeing the ground conductor in the cords, lamp enclosures and power outlets burn back and melt. It struck me that current from the welder was escaping to earth through this path.

After grounding each table separately those problems went away.

Also I am required to install a separate ground rod on most of the CNC machines I have supplied the service conductors to. This is through a concrete floor, in the middle of a mature facility. Often there has been a little resistance in the ground when the rod was initially driven and when I mentioned this to the installation techs that come out when you buy a new machine they would check and it has so far been the case that after the rod has been in the soil a few days the resistance has declined to acceptable limits.
 

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The only reason a ground fault breaker prevents shock is because the breaker kicks the second the ground sees even a small amount of current.
Yes. A GFCI has 3 modes of operation:

1. Overcurrent (just like a regular breaker)
2. Current flowing "out" the hot lead does not equal current flowing "back" on the neutral. This means it is flowing through a path to ground someplace external to the circuit, like you!
3. Current flowing through the safety ground. A regular breaker would trip in this situation only if the current was in excess of the breaker rating, such as a short inside the device from hot to the case.

Al
 

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We had fluorescent fixture hung with light chain over the top of our welding tables. The cross brace they were suspended from was constructed with thin walled square tubing that was welded directly to the table. These lights were often plugged into those power outlets many folks use for computers and monitors and such.The guys may have small fans, radios or a rotating weld positioner along with the lights.
We were seeing the ground conductor in the cords, lamp enclosures and power outlets burn back and melt. It struck me that current from the welder was escaping to earth through this path.

After grounding each table separately those problems went away.

Also I am required to install a separate ground rod on most of the CNC machines I have supplied the service conductors to. This is through a concrete floor, in the middle of a mature facility. Often there has been a little resistance in the ground when the rod was initially driven and when I mentioned this to the installation techs that come out when you buy a new machine they would check and it has so far been the case that after the rod has been in the soil a few days the resistance has declined to acceptable limits.

I would imagine that an outlet at the welding table should be in a metal enclosure, which would have been grounded. This should provide a low resistance path and keep the wires from melting. There should be another ground in the lighting fixture, but it might not help much depending on how it is hanging. Of course this doesn't work if the light is plugged into a wall outlet.

The CNC machines are kind of a different animal. They are required to be grounded just like any electrical appliance (metal). Is the separate ground rod a manufacturer requirement?
 

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For the life of me I don't understand why you would want to put an earth ground on a welding table. It is not a power source.
A bodily shock is only going to happen when your body provides a return path to the source through the ground you are standing on IF one side of that source is grounded also.
That's why you can touch one side of the welder's output terminals and not feel a thing because that current is only trying to get to the other terminal of the welder and as long as that other side isn't laying on the ground......you're safe.
That ground rod on your electrical panel isn't there for your safety, It's there to keep from burning the building down and trip a breaker should a fault occur in an appliance.
Shockingly :mocking: your generator is safer in that regard than your home's electrical system if it's sitting on an insulated surface.

You might want to re-think the safety part of your sentence. :drinks:
 

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I do not have a separate ground to the table are usually just clamp to what I am working on.

And a motor vehicle or tractor I try to unhook the battery and alternator if I can but nowadays it is very tough to get to them. In that case I grind a shiny spot on the piece I am welding on put a vice grips on that and clamp my ground to the vice grips so that the ground clamp cannot slide off of the fresh grind. The current will always try to find the easiest route. I would not clamp to any other piece of metal just in case the current takes a different route. I have never had a problem doing this but I am sure some would give me heck.
 

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Yes. A GFCI has 3 modes of operation:

1. Overcurrent (just like a regular breaker)
2. Current flowing "out" the hot lead does not equal current flowing "back" on the neutral. This means it is flowing through a path to ground someplace external to the circuit, like you!
3. Current flowing through the safety ground. A regular breaker would trip in this situation only if the current was in excess of the breaker rating, such as a short inside the device from hot to the case.

Al
Exactly what I said!! :thumbup1gif:
 
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