grounding

[paulrbrown]

"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."

This is not always the case, if you 'saftey ground', [the green wire on the AC input of the machine], to the steel building or conduit, as most AC is ,the welding current will have a path back to the welder which is 'saftey grounded' to the welder case. The 'Saftey Ground' is now a conductor of welding current. Any electrical devices coming in contact with the work piece that are 'saftey grounded ' will now have welding current flowing through them, even when not welding, as the work lead has about 50% of the OCV going thru it, this info came from Miller's Saftey Dept. Also, the case of the welder is now electrically hot along with the table it is sitting on and or cart, unless there is some sort of insulation between them. I have seen it and saw electric drills and grinders arc when coming in contact with the work piece, and if welding is going on, the arc is quite impressive. A person was almost killed by touching the case of a Dynasty 300 and the work piece at the same time while welding was going on. If you can strike an arc off your machine case, you can bet you are sending welding current back thru the saftey ground. There is also the concern of fire, because an unknown amout of current is now flowing thru the very small 'Saftey Ground'. If you guys don't believe, call Miller's saftey man in Appleton, I know because I did.

Hope this sheds some light on a dangerous Situation. Paul Brown

[Sberry]

Paul,, see if you can strike an arc on the side of that machine if it is insulated from the work ground,,, definately not! It will if it is sitting on a bench the work ground is connected to. These machines are used on ships and buildings that are grounded all the time. We are confusing some things here. There have been instances where ground loops have been setup and the equipment grounding has become an alternate path for secondary grounds, such as for example, 2 benches, with the machine sitting on one and the work lead grounded to that bench and take the lead and welding on another bench with a grounded circuit attatched to it or a grounded drill laying on it. This creates a ground loop thru the building wiring. But as far as there being some passable connection between the secondary and the case ground,,, definately not. It would set up a ground loop on every arc strike when working on grounded machinery. Yes, I agree with dyn88 on the hi freq issues in the big shop, but this thread has turned a bit here. But Paul, dont you think this would make thse machines inherantly unsafe then? You can see the complete seperation of primary and secondary on the electrical schematic.

[fun4now]

hi freek

i think the hole high frequency thing is realy clouding the ground subject.

if it helps on page 16 of the downloadable miller TIG handbook the high frequency is coverd and it seems to run amuck all over. long and short is a ground on the table will have no real efects.

[FM117]

I have an older Lincoln 300 that sounds like the same thing
Dyn88 has used. The owners manual for it talks about actually
connecting a lead from the "work" terminal to an earth ground
within 10 feet of the unit using the same size cable as the work
lead. The manual also calls for the welder frame be grounded. It
mentions that the work lead is NOT a welder case ground.
I have my work lead grounded to a copper grounding rod so
my bench would also be when the lead is hooked up. The welder
is grounded back to the service box.
I've never had any problems using it set up this way, except
the high freq. will sometimes cause the" mad" ( magnetic anomaly detectors)
on my burgler alarm system to trip.
I gotta do some more research on this ground thing....maybe a call
to Lincoln service.
Dave P.

[Sberry]

I havent read the Lincoln thing on Hi-freq but have read the Miller manual and one of the main things is to shield the wiring in the imediate area which means conduit. I would assume your MAD could be shielded, maybe even foil or make some raceway covers. As dyn88 pointed out, if its a problem you have to do what you got to do. When I set mine up I asked the engineer and he said if there isnt a problem dont worry about it. My building is well grounded, steel, and my benches are bonded to it as is the electric and the welding secondaries, I never have a problem and my use is only occasional anyway. I did however go to great pains as my benches are interconnected to avoid ground loops thru the electric system from welding. In this system what I finally did was to install the 120V power to the benches with only 2 wire feed and use the welding bond to the building as the ground fault return. I did feed it from GFCI circuit to. This way grounded tools sitting on the bench cant carry a welding current.

[FM117]

Sberry
It's wired in metal conduit. The alarm is no big deal I
just turn off the mad sensors if I'm welding at night
after the alarm auto arms....no big deal, just mentioned
it as a side effect of the High freq.
Dave P.

[Justin00Stang]

If you look in the miller manual that comes with your tig machine they recomend grounding just about everything that is metal and nearby, to earth if you have any HF interference problems.

My old DSL modem would sometimes drop out when doing Al. on my sync 250 (HF continuous). New one seems to work okay though. I did add a 2nd earth ground right near the welder power receptacle. Didn't ground anything else though.

[Grumpy]

This thread seems to be relative to fixed machinery and to a fixed electrical system. What about a portable engine driven welder? Miller's own educational material states the following: "Connections typically used for grounding an engine-driven welding machine include a cable connected from a ground stud on the welding machine to a metal stake placed in the ground." (emphasis added).

Does this mean I should have a grounding cable from the ground stud to a grounding rod? What happens when you roll the portable, say from one spot in a shop to another? Another ground?

I thought I had this all figured out but now I'm .

[fun4now]

Grumpy

Connections typically used for grounding an engine-driven welding machine include a cable connected from a ground stud on the welding machine to a metal stake placed in the ground." (emphasis added).


Does this mean I should have a grounding cable from the ground stud to a grounding rod? What happens when you roll the portable, say from one spot in a shop to another? Another ground?

i think it refers to in the field with a removable stake. as for in the shop i would use the panel ground as it will lead to a stake from the pannel.

just an opinion

[Sberry]

The only time I would thik it would matter to pound a ground stake is if you had a wire outlet on he machine connected to the premise wiring where you wanted to eleminate step voltages between the ground you are standing on and the machine or the building. This is going to get complicated.
The panels in separate buildings are not really subpanels as far as code is concerned. They are the service equipment for the structure. You can have a subpanel from the service equipment in each building if you want. Between buildings, section 250.32 applies and if there are metal interconnections between buildings such as water piping, or air lines, or any metal interconnection at all, then you must install an equipment ground wire so if you have a 120/240 system, you would have four wires. The neutral would be separated in each building and a grounding bar would be installed, just like a subpanel. Then the code requires a grounding electrode conductor (GEC) to a grounding electrode (usually a ground rod). The GEC will be connected to the equipment ground bar at each building. This is not to clear overcurrent devices, this is for two reasons. One is lightning, the more important one is to put the equipment ground at the same relative potential as the earth. This is for step potential or touch potential voltages so that what you touch in the building is at the same potential as what you are standing on. Now the tricky part. If you do not have any interconnecting metal between buildings, the code allows you to install three conductors between buildings. When you do this you bond the neutral and ground the neutral just like a new service. Some inspectors think that every panel in a separate building must be treated as a subpanel, but this is not true. In past codes (1996 and older) these rule were in section 250-24 and Exception 2 addressed the grounding bus.
4 wire would already take care of it. I can tell you this, no one does it. With plug and cord connected equipment to the machine I doubt it would matter. This part I coppied above explains some of the "why" we use a ground stake.

[HAWK]

Grumpy,

When running the Trailblazer mobile I only ran a ground rod for two situations. (1) When using an HF box for TIG (2) When supplying AUX power to my residence. In addition to the machine ground stud going to an 8' ground rod I also made use of all four plug wires: 2 hots, neutral, and ground. The ground and neutral from the AUX plug were tied back to the feed panel neutral buss. I think Sberry has it well covered!!!

[cope]

Sberry

Cary, I worked for a mobile emissions testing company for 4 years. We had mobile lab trailers which we ran off of Gen set or cutomer power depending on what was available. We always ran a ground rod from the trailer and often from the gen set. We had a different situation from a typical welding rig; 5-6 analyzers , PC, printer and a chart recorder. We had more problems with customer power being supplied improperly than we did with our own gen set power.

[dyn88]

wow beat that horse. Normally when you run a generater you need to ground it to allow the static charge to discharge to a safe place. you dont want to ruin any expensive electronics.