I appologize if this looks like I'm trying to turn this into my own training session and one up Jody, it's not the case and Jody has mentioned in at least once but I think those of you who are just starting out need this reinforced because of the use of HF start and the problems it can cause. There's a proper way to cure that problem.
This is something that drives me nuts and makes me mad at the same time so I hope ya'll all don't mind me venting a little.
The atachment in this post is wrong. It can't be be both Earth/Ground and Negative -ve. It is Negative or Positive Voltage depending upon the welder mode.
I don't want to go PHd on you but if you can understand why this is wrong then setting up your TIG or MIG welder correctly will definitely be much easier.
When I was a young buck I messed around with the DC motors in my electric train set and slot cars. I knew from those that I had a transformer and one side of the track was negative and the other positive and they both needed to be there or the train wouldn't run.
Then I found out about A/C. I had a hot and a neutral. There was a ground but it was just to the case of the transformer and I usually left it off because my dad told me it was just so I wouldn't get shocked. Because I was use to working with batteries and transformers I naturally assumed the neutral was the negative and the other one was the positive.
Then I opened up my first household distribution panel and guess what? That ground wire was connected to the same place as the neutral.. Ah ha, my dad was wrong, the ground is the negative!!! Uhh not so fast grass hopper..
My Dad then explained to me about a 220v motor and how it can be wired for both 110 or 220. And he showed me how to do it without the neutral but for safety's sake we put a ground wire on the frame and tied it to the copper water line that went into the EARTH... If for some reason the motor threw a winding and it touched the case that voltage would go to ground/earth and not into you because earth is the path of least resisance. Are you starting to see where I'm going with this?
I told you no PhD required here so I'll keep it simple. A/C is what it say's it is. Alternating and it normally alternates from postive to negative in exactly the same proportion. Within a single wire you have both the positive voltage and the negative voltage you need to create a difference in potential and cause current to flow. Thats enough, you can research the rest on your own if you want.
The point is this: In DCEN mode the work cable is positive and the torch electrode is negative. If you put a ground (earth) clamp on your work piece or your welding table the path of least resitance to a difference in potential will be the earth and some or all of the current will flow to it rather than your torch. The same thing happens in DCEP mode but you won't notice it as much and it's why a MIG welder can work without the work cable connected. In A/C mode about half of your energy (current) could potentially be wasted.
So what's my point? The danged cable is called a work cable and not Earth or Ground because depending upon your welding mode it can be positve, negative or both. But it will never be a ground or your welder will never work correctly.
Armed with that, you can now see that current flows in a welder from negative to positive whether its A/C or DC and all those fancy knobs and dials on your inverter TIG should start to make some sense.
O.K. So now your asking why your welder has a ground wire on the plug. This is just incase something shorts inside and touches the case to make it hot. If you touch the case when that's happening you'll get a little tingle but you won't get knocked on your butt. That's all, the welder doesn't need it to run.
sorry to nitpick, but when you clamp the work clamp to a grounded object, you can still weld. why? because the power supply of a welder is isolated and floating relative to ground. so, the work clamp, in most cases, really is a ground clamp. as you pointed out ground doesn't automatically mean the negative lead, it means that it's referenced as 0 volts with respect to the earth. so, in the case of DCEN, the torch or mig tip is at a negative voltage relative to ground.
I haven't tested this, but I'd be curious to find out if the newer inverter based welders are still isolated, or is the clamp tied to ground in the machine and the polarity switch switching both poles of the power supply. in practice, it doesn't matter, but it's a curiosity. I went to school for electrical engineering for a while before I figured out that you don't get to make anything as an engineer and left.
now that I think about it, the ground clamp might be tied to mains neutral (effectively ground) on a transformer machine. if the switch changes both poles of the power supply it wouldn't matter if it were floating. that might make more sense, as if the output were truly left floating, the voltage could climb to many hundreds or thousands of volts above ground if you forgot to clamp the clamp to something.
I haven't tested this, but I'd be curious to find out if the newer inverter based welders are still isolated, or is the clamp tied to ground in the machine and the polarity switch switching both poles of the power supply. in practice, it doesn't matter, but it's a curiosity. I went to school for electrical engineering for a while before I figured out that you don't get to make anything as an engineer and left.
now that I think about it, the ground clamp might be tied to mains neutral (effectively ground) on a transformer machine. if the switch changes both poles of the power supply it wouldn't matter if it were floating. that might make more sense, as if the output were truly left floating, the voltage could climb to many hundreds or thousands of volts above ground if you forgot to clamp the clamp to something.
No argument that it will still weld but I would argue that if you set up your welder on a table that was earth grounded and found the ideal settings and then removed the ground your settings might need to be changed. You're probably an excellent welder and would unconciously adjust at the foot pedal.
Anywhoo... the point was that the work cable is not a earth/ground it is a conductor that completes a circuit required for the machine to operate as designed. In my Lincoln Precision TIG 225 the manual clearly states that the machine does not need the ground to operate but the machine could potentially become a shock hazard and therefore it must be installed. Again, not because the machine needs it but because the law requires it.
Anywhoo... the point was that the work cable is not a earth/ground it is a conductor that completes a circuit required for the machine to operate as designed. In my Lincoln Precision TIG 225 the manual clearly states that the machine does not need the ground to operate but the machine could potentially become a shock hazard and therefore it must be installed. Again, not because the machine needs it but because the law requires it.
Highly skilled at turning expensive pieces of metal into useless but recyclable crap..
my point is that the term 'ground' is just a voltage reference. I'll have to measure my dad's when I go visit for christmas (precision tig 185), but I think, now that I think about it, that the work clamp should be referenced to mains neutral. which mains neutral should be the same potential as the ground wire. the ground wire is there for a redundant path to earth in case something fails short to the machine chassis AND the neutral wire fails. ground and neutral are bonded together, as you mentioned earlier, at the breaker box.
anyway, enough of the EE crap, It doesn't really matter much to your welder what ground is or whether any part of it's circuitry is at or near ground potential from a theoretical perspective. basically, you've got 2 current loops you're concerned about: out your torch and back through your workpiece cable and to and from the breaker to the machine.
furthermore, I think ground clamp is just more descriptive, as regardless of whether the clamp is attached to safety ground from the wall, the ground clamp will be at circuit ground potential. 'work clamp' sounds pretty generic to me. it could be a vice. or a vice grip. or the clamp on your welder.
and, re-reading your first post, I think you're interpreting the flow of electricity slightly off. positive and negative are relative terms, not absolute. 'ground' is the common(usually negative) half of a circuit.
here's a simplified picture of a welder, electrically speaking.
D1 is the rectifier diode (DCEP in this picture)
C1 is the smoothing capacitor
TX1 is the main transformer
one side of the transformer secondary, one side of the smoothing cap, the ground clamp and (I think, will have to measure) and safety ground are connected together. the red path shows the welding current with the clamp connected. now, think of how far that current has to travel if you don't connect the clamp. from the workpiece to the floor, across the floor/ground to the copper rod in the ground outside, back through the panel and in-wall wiring, though the cable to the welder, and back the the machine. so, even if the clamp and ground are electrically connected, without the ground clamp.
I hope this isn't pedantic. I just like electricity a lot.
if anyone's interested, i can probably put together a much better diagram and description of what's going on in your welder. personally, I take a balanced approach to PhD vs hard knocks. there is something to be said for being informed. there is also something to be said for getting the job done.
anyway, enough of the EE crap, It doesn't really matter much to your welder what ground is or whether any part of it's circuitry is at or near ground potential from a theoretical perspective. basically, you've got 2 current loops you're concerned about: out your torch and back through your workpiece cable and to and from the breaker to the machine.
furthermore, I think ground clamp is just more descriptive, as regardless of whether the clamp is attached to safety ground from the wall, the ground clamp will be at circuit ground potential. 'work clamp' sounds pretty generic to me. it could be a vice. or a vice grip. or the clamp on your welder.
and, re-reading your first post, I think you're interpreting the flow of electricity slightly off. positive and negative are relative terms, not absolute. 'ground' is the common(usually negative) half of a circuit.
here's a simplified picture of a welder, electrically speaking.
D1 is the rectifier diode (DCEP in this picture)
C1 is the smoothing capacitor
TX1 is the main transformer
one side of the transformer secondary, one side of the smoothing cap, the ground clamp and (I think, will have to measure) and safety ground are connected together. the red path shows the welding current with the clamp connected. now, think of how far that current has to travel if you don't connect the clamp. from the workpiece to the floor, across the floor/ground to the copper rod in the ground outside, back through the panel and in-wall wiring, though the cable to the welder, and back the the machine. so, even if the clamp and ground are electrically connected, without the ground clamp.
I hope this isn't pedantic. I just like electricity a lot.
if anyone's interested, i can probably put together a much better diagram and description of what's going on in your welder. personally, I take a balanced approach to PhD vs hard knocks. there is something to be said for being informed. there is also something to be said for getting the job done.
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O.K. That circuit will work for a 120v welder. But just for a moment, remove the transformer and rectifier and replace it with a car battery. Do you still need the earth?
The 120v single phase circuit is really not very efficient. If you used 220V two phase power what would your circuit look like. Would you still need the earth?
Like I said in the original post, this is not for PhD's if anyone needs more info on how and why this works, there are plenty of basic electricity books out there that will explain it in full. I could stretch this post out into a million lines of theory but no one would read it and the point would be lost.
Steve
The 120v single phase circuit is really not very efficient. If you used 220V two phase power what would your circuit look like. Would you still need the earth?
Like I said in the original post, this is not for PhD's if anyone needs more info on how and why this works, there are plenty of basic electricity books out there that will explain it in full. I could stretch this post out into a million lines of theory but no one would read it and the point would be lost.
Steve
Highly skilled at turning expensive pieces of metal into useless but recyclable crap..