grounding

[themodernartist]

Howdy from the neophite welder,
I am totally in love with my Dynasty 200 DX. Just finished my first project, a hi-tech carry all gurny made from aluminum. I was just wondering, if you have an all metal work table, should it be grounded? I mean like running a cable to GROUND like the one that goes to "earth" on your electrical in your home or business. Please give me reasons why or why not.
Thanks,
Happy

[dyn88]

not commonly done, unless there are interferance issues with the high frequency(which you probably arent using continuously).

[Sberry]

Only if there is a chance it can become energized from some primary electrical source. It isnt a bad idea to feed any tools you use around it from a GFI recept. For most purposes "grounding equipment" does not mean grounding to earth, it means connecting a ground fault means back to the neutral at the service entrance.

[fun4now]

if you were to ground your table to earth would it interfeer with your work lead ?

most of the time i atach my work lead to the table and just clamp my work to the table. how would that work if i grounded(to earth) my table?

[INTP]

if you were to ground your table to earth would it interfeer with your work lead ?

most of the time i atach my work lead to the table and just clamp my work to the table. how would that work if i grounded(to earth) my table?

Better yet, what would happen when you switched polarity?

I've never grounded my table. You have to be careful though to always have the work clamp on the part or the work clamp on the table (and the part on the table) or else you could get a situation where there's no return path to the welder. This is a scenario where the grounded table would help, because it would be the path, not you! A good habit is to always put the work clamp on the part or the table before turning on the welder, and never move it except between the two until it's turned off.

[Sberry]

It wont really hurt anything to ground your bench to the earth,, but,,, why?
(I've never grounded my table. You have to be careful though to always have the work clamp on the part or the work clamp on the table (and the part on the table) or else you could get a situation where there's no return path to the welder. This is a scenario where the grounded table would help, because it would be the path, not you! A good habit is to always put the work clamp on the part or the table before turning on the welder, and never move it except between the two until it's turned off.)
How would this help anything? There is no return path to the welder from the secondary (output) except for thru the ground lead. We are confusing primary and secondary here. They are isolated from each other. For sake of this discussion here we need to understand what equipment ground means. It is a low impedance or low resistance path to return a fault, which is a short to ground, back to the transformer allowing enough current to pass quickly enough to trip a breaker. The earth will not do this, there is too much resistance and it wont pass enough current to trip. All this has nothing to do with the outputs on the machine. There was a long thread on Hobart that went into all this in detail. I forget what it was called. Also this has nothing to do with changing polarity, again, secondary is an isolated system.

[fun4now]

ummm in short form 1 thing has nothing to do with the other

although the work lead is offen (rongly) referd to as the ground it in fact is not a ground, as is grounding the outside of a motor or table saw for instant's

thanks

[Sberry]

Correct, it is the work ground, not connected to the equipment ground.

[HAWK]

There have been instances where earth grounding the work table actually caused poor welder performance. This has occurred only a few machines, mostly prototypes, and was corrected before a markteting release. I am not speaking of any particular brand here.

[tackit]

I thought there was a rule where you are not supposed to have more than one earth ground every so many feet from another one, (called nesting???) perhaps if the welding table's earth ground was to close to the mains earth ground there could be problems.

[INTP]

It wont really hurt anything to ground your bench to the earth,, but,,, why?
...
How would this help anything? There is no return path to the welder from the secondary (output) except for thru the ground lead. We are confusing primary and secondary here. They are isolated from each other. For sake of this discussion here we need to understand what equipment ground means. It is a low impedance or low resistance path to return a fault, which is a short to ground, back to the transformer allowing enough current to pass quickly enough to trip a breaker. The earth will not do this, there is too much resistance and it wont pass enough current to trip. All this has nothing to do with the outputs on the machine. There was a long thread on Hobart that went into all this in detail. I forget what it was called. Also this has nothing to do with changing polarity, again, secondary is an isolated system.

I was assuming that the grounded table would have a low impedence path to earth. If we cannot count on the earth ground being low impedence, then there is a problem with calling it anything other than another wire.

How it would help is this. I'm not talking about tripping breakers, I'm talking about voltage difference. It is indeed true that the coils inside the welder are independent of the wiring circuits. But I'm quite sure that when the welding circuit is energized, there is a voltage difference between the welding gun/stick/torch and the earth/neutral. If you put a voltmeter between the lead and a proper ground, I'm sure you'd have a potential. If you put yourself between the two, you'd likely get shocked. In this case you're the same potential as the ground, but with a grounded table, the table has less resisistance than you do, which makes your body a less likely path for this current. No, the breaker probably won't trip, but you'll stop when you realize you're not striking the arc you expected, then realize that you forgot to connect the work clamp.

I acknowledge that this is NOT the reason for grounds as it applies to wiring circuits themselves, and I certainly agree with your points about tripping or not tripping breakers.

[Sberry]

If you have a potential difference between the lead and ground there is something wrong with the machine. There should be none and it will not help with a shock hazzard from the secondary by grounding the bench to the earth. Even at 120V and ideal conditions the earth will pass only an amp or so of current, the welding machine secondary has way less voltage, grounding the bench is completely useless other than to protect it from a fault of a primary circuit,, and then it would have to be connected to the electric system ground to be of any value.

[Sberry]

Turn the machine off and put an ohm meter between the leads and the machine case,, nothing. Think about it this way, if they were not isolated there would be a secondary path for the welding currents if one was welding on anything grounded such as a steel building.

[themodernartist]

grounding question

Howdy,
My thanks to all of you guys that responded to my question on grounding.
That clears it up for me.
Happy

[dyn88]

Ok here it is-When I worked for Moroso performance products/Competition Engineering, There was a problem with the CNC depatment recieving files from R and D( they came incomplete, confusing the machines because the blocks of code were not full.). Also the phone system would always hum in the back portion of the facility. They had an engineer from the FCC come in and do an inspection. He found that not only were the points in over half the machines over gapped, None of the benches were grounded to earth! Now when you have 14 lincoln ideal arc 300's half of which welding aluminum 10 hours a day all day(production dont you know), There is bound to be some h/f interferance. after all the benches were grounded and the machines the preexisting problem was solved. Every two machines and benches got a 12foot long 1/2 inch copper rod driven into the earth and wired to it. Nobody noticed any difference in the quality of arc or weld(and some of these guys could tell if the incoming line voltage swayed). So in most cases no, earthing your welding bench does not effect the machine or the weld. This is not to say that there arent special cases out there that wouldnt have the same effect(no inverters were there when I was).