Grounding the work table

[CraigJ]

I am new to TIG and am waiting for my 225LX to arrive. I have a steel table that I have used for gas and stick welding in the past, frequently just clamping the work electrode to the table near the work. My question is about safety grounding the table to earth. I suspect that neither the + nor -- outputs of the welder are grounded, as the 225LX can also be used for stick on both straight (DCEN) and reversed (DCEP) polarity. If the table isn't grounded, I can see how a short in the machine might make the table hot.

I have run a wire from a new ground rod into the shop, connecting it to the ground at the outlet to give a shorter path to ground. Is it sufficient to run a ground wire (not the work clamp) to the table from the chassis lug on the back of the welder? I can also connect the table to the termination of the wire from the ground rod. Any suggestions on wire size? #6 would be needed to carry the full welder output.

CraigJ

[geezer]

I fail to see the advantage to grounding your welding table, if there is a short in the machine you already have a ground on the plug which should take care of that issue, current coming out the machine still needs to complete a circut + or neg makes no diff whether one is earth clamp or stinger. If you follow your logic on needing a grounded work table then every thing you welded would need a special ground to it before you start welding on it.

At least that's the way I see it, not to say I haven;t been wrong before, but to me grounding the welding table doesn;t make sense. Please correct me if I'm wrong on this.

[sportbike]

I don't think I have ever seen a grounded table. Not to say it may not be possible to zap yourself.

We have had HF grounding issues while welding Titanium in a computer controlled environmental chamber, but that just made the computer reboot.

[revkev6]

I don't see a need for a ground but I don't see how it could hurt either.

[67cudafb]

Really don't see need to ground steel welding table unless you have wired electric outlets or bench grinder an such then I would be sure to ground table. Be sure all grounds in shop are tied together or you create imbalance in ground field which can lead to other problems.

[performance]

Grounding the table isn't necessary nor practical.

[CraigJ]

In reply to Geezer, this is the way a welder fault could be hazardous: in normal tig setup, the machine has a short from negative (torch) to chassis. The work clamp, and the table are now at 60-80 volts above ground before the arc ignites. Could result in anything from a mild shock to electrocution, depending on how much you are sweating, what you are standing on, your shoes, etc. Maybe this is unlikely, but fault circuits are there to protect you in unusual circumstances.

Craig

[geezer]

In reply to Geezer, this is the way a welder fault could be hazardous: in normal tig setup, the machine has a short from negative (torch) to chassis. The work clamp, and the table are now at 60-80 volts above ground before the arc ignites. Could result in anything from a mild shock to electrocution, depending on how much you are sweating, what you are standing on, your shoes, etc. Maybe this is unlikely, but fault circuits are there to protect you in unusual circumstances.

Craig

Could happen, which brings up the simple safety rule, always place your earth clamp as close to your work as possible and never position your body between the earth clamp and the torch.

As far as special grounding goes I have seen old timers ground out pieces on large equipment they are welding on to prevent ball bearings on the machines they are welding repairs on from arcing. Does it help, dunno but it can't hurt.

[performance]

Grounding the table will not prevent shock or electrocution or even shock. The welder "grounds" itself. People forget the ground is the welder, not earth itself. Without this return path the unit will not weld...nor produce power. The thing you have to do is NOT become a path for current to run along. I've welded on "grounded" things, and if you insert yourself between the work and the torch or somehow make yourself a conductor, you will get shocked. As remarked, the closest you can make the work clamp, to the work, the less likely you'll get a tingle that will make you jingle (or tinkle )

Ground it for you peace of mind for sure, but its not a real world scenario and won't greatly decrease your chances of getting shocked. If you are wet or damp, you're going to feel it one way or the other.

[67cudafb]

I get where if you put yourself in the path you could get shocked but I did not relize electrocution from a welder was possible wow!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[CraigJ]

Grounding the table will not prevent shock or electrocution or even shock. The welder "grounds" itself. People forget the ground is the welder, not earth itself. Without this return path the unit will not weld...nor produce power. The thing you have to do is NOT become a path for current to run along. I've welded on "grounded" things, and if you insert yourself between the work and the torch or somehow make yourself a conductor, you will get shocked. As remarked, the closest you can make the work clamp, to the work, the less likely you'll get a tingle that will make you jingle (or tinkle )

Ground it for you peace of mind for sure, but its not a real world scenario and won't greatly decrease your chances of getting shocked. If you are wet or damp, you're going to feel it one way or the other.

Thanks for all of your thoughts. I think there may be a misunderstanding of terms here: while "ground" is the common term for the work lead that carries current, I am talking about safety ground, ("earth ground"), that the green wire in the power cord is connected to, which is also the potential of our bodies through capacitative coupling to our surroundings. If the welding machine has an internal short to chassis (on the torch side), the work lead could become hot with respect to chassis ground. With the work lead clamped to a metal table, the whole table would be above ground potential. So you would only need to touch the table to risk a shock. That is a different scenario than getting between the work electrode and the torch.

Perhaps I am wrong about the welding machines' internal connections. When mine arrives, I will check with an ohmmeter to see if either output is connected to chassis.

CraigJ

____________
While I am a total newbie to TIG, I am also an electrical engineer with over 30 years experience designing electronic test instruments, which have to meet stringent safety requirements...

[performance]

The welder is grounded to chassis, but the rubber feet insulate it...But if its on a cart,(which many welders are) it won't matter anyway.

[CraigJ]

The welder is grounded to chassis, but the rubber feet insulate it...But if its on a cart,(which many welders are) it won't matter anyway.

Mark: By that do you mean that the TIG work lead (the + output terminal) is connected to chassis? If so, is that condition also true in stick mode, where the work lead would be moved to the negative output? If so, then DCEP stick mode would put the work clamp at up to 80V below chassis (green wire) ground.

Craig

[performance]

I am referring to the input wires only.

The welder output isn't grounded to the chassis directly.

[CraigJ]

Mark:
I don't want to flog this to death, so I'll just try once more to get across what I was asking about: if the welding machine's outputs (either one) are not connected to chassis, then if a short in the machine were to happen between the torch output and chassis ground, the work clamp and anything it was connected to (like the table) would move the full output voltage off of chassis ground, all without tripping any breakers or shorting the machine's output. But the work and table would be dangerously hot. Undoubtedly this is not a common occurrence, but certainly possible. That is why it seems to me that the work table should be earthed for safety. This could be done with a wire from the welder's chassis to the table.

From the other posts I gather that grounding the work table is not common practice. But in the unlikely event of the wrong kind of internal machine malfunction, it might save you from a bad shock.

Thanks again for the thoughts and comments.
Craig

[performance]

What it will do is cause welding issues and increase the likelihood of damage to the unit, should you have an issue, and the feedback gets put back on the welder. The welder won't short out in the fashion you mention. You are dealing with a inverter and not direct raw power. The units are also equipped with a built in breaker switch.
I've seen "electrical engineers" overthink this, because they try to approach it from a technical standpoint, when in fact a welder is generally an exception to the rule. The welder does have a separate ground lug, but its for using a "bonded" ground to a rod outdoors to ground for HF issues. You have a ground wire that handles internal shorts within the unit.

[ogorir]

I believe mark's right here.

if there's a fault in the machine that shorts one of the welding leads to the case, the internal breaker OR your wall breaker will trip. the only situation that I can see that would make the table hot is if the hot lead shorted to the case (giving it a ground reference) and the work lead shorted to mains voltage, or somewhere on the high-side of the inverter. I don't actually think that's remotely possible.

the only issue i see with grounding the table anyway is contaminating your building's ground. on the other hand, if you were to run a dedicated ground to a separate grounding rod outside, it would actually probably help your noise situation (at least with HF tig)

anyway, the real point here is if there was even a small chance of the work leads being 'hot,'* the machines wouldn'tve been approved for sale in this country. UL rules are pretty crazy regarding this kind of stuff.

*hot is a relative term. the OCV on a stick welder will shock the crap out of you, if you're stupid, same with a tig. if you were to stab someone in the chest with a stick electrode with the welder on, it would kill them pretty easily. the real issue is keeping mains AC off of your work outputs, as mains AC is significantly more dangerous. (higher voltage and as far as your body is concerned, unlimited amperage)

[CraigJ]

I believe mark's right here.

if there's a fault in the machine that shorts one of the welding leads to the case, the internal breaker OR your wall breaker will trip. the only situation that I can see that would make the table hot is if the hot lead shorted to the case (giving it a ground reference) and the work lead shorted to mains voltage, or somewhere on the high-side of the inverter. I don't actually think that's remotely possible.

the only issue i see with grounding the table anyway is contaminating your building's ground. on the other hand, if you were to run a dedicated ground to a separate grounding rod outside, it would actually probably help your noise situation (at least with HF tig)

anyway, the real point here is if there was even a small chance of the work leads being 'hot,'* the machines wouldn'tve been approved for sale in this country. UL rules are pretty crazy regarding this kind of stuff.

*hot is a relative term. the OCV on a stick welder will shock the crap out of you, if you're stupid, same with a tig. if you were to stab someone in the chest with a stick electrode with the welder on, it would kill them pretty easily. the real issue is keeping mains AC off of your work outputs, as mains AC is significantly more dangerous. (higher voltage and as far as your body is concerned, unlimited amperage)

MacGuire: As you said in the first paragraph, if the torch output shorts to the case (which is connected earth ground through the power cord) the work lead will be hot -- 60-80 volts above ground. That fault alone would make the work table dangerously hot; no other fault is needed. And since the welder's outputs are floating with respect to chassis, the welder would not see a fault condition or trip out. If the table were separately grounded to earth, it would short out the welder's output but protect the person touching it, a better outcome in my opinion.

I checked the owner's manual for the Lincoln Invertec V205, which appears to have similar outputs to the 225LX. In fact, they show the work lead being connected to + for TIG and - for stick. They also clearly advise that the table and workpiece be grounded. I checked at the local community college welding shop, which uses the Lincoln inverters, and their tables are not separately bonded to earth ground. All of which goes to show that while it might be a good idea, most welders don't bother. The risk may be slight but the consequences potentially serious, so I will ground my table and cart unless it proves to cause damage to the welder or increases the HF radiation (which I think will actually be improved). Each to his own!

[ogorir]

MacGuire: As you said in the first paragraph, if the torch output shorts to the case (which is connected earth ground through the power cord) the work lead will be hot -- 60-80 volts above ground. That fault alone would make the work table dangerously hot; no other fault is needed. And since the welder's outputs are floating with respect to chassis, the welder would not see a fault condition or trip out. If the table were separately grounded to earth, it would short out the welder's output but protect the person touching it, a better outcome in my opinion.

I see where you're going with that, but if the torch output shorts to the case, it should trip the breaker. if it didn't, to realize the potential you're talking about, you'd need to be touching the case and your welding table.

you shouldn't have any issues if you bond your table to ground separately from your electrical system ground. same protection, no possibility of noise contamination.

[CraigJ]

MacGuire: You say that if the torch output gets shorted to chassis, the breaker will trip. I think this unlikely. If the work clamp lead (+ output) were shorted to the chassis would the breaker trip? I think not. So just reverse the torch and work lead, like you would for stick, and short that same + output to chassis. No difference for the machine, right? But now the work clamp is at -80V (or whatever the open circuit voltage is), and the workpiece and table are hot.

The only way this wouldn't be true is if the machine is automatically connecting the correct work lead terminal to ground when switching between TIG and STICK. But if it does, then DCEN stick would not be safe...and the manual certainly doesn't say that is not allowed.

Although I never expected to post this many times on this subject, thanks for the discussion. I won't take any more bandwidth with this until I get my 225 LX -- then I will measure whether the output is floating or not and resolve it. I invite any of you to look at your machines to see if either terminal is connected to chassis. Unless you have a transformer welder with a big switch on the front marked +, AC, -, I'll bet your inverter's outputs are floating so that either polarity can be used.

In the mean time, I can hardly wait to start laying some beads!