Machine Ground, Is It Necessary?

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Is it necessary to ground you welding machine chassis? All machines that I have used have a chassis ground that attaches to the case or frame for a wire going to an earth ground but I have never seen it done. What purpose does it serve?Last edited by Aircamperace; 11-18-2012 at 09:02 AM.
Reply:If the welder is plugged into a properly wired electrical system then it is grounded to ground.  Mac
Reply:Originally Posted by Tool MakerIf the welder is plugged into a properly wired electrical system then it is grounded to ground.  Mac
Reply:I think I asked this same question here a while back, and I consulted with my electrician friend. What I believe is that it is to connect to a ground rod, in the earth, when you are using the generator as back up to power a house. Although, I don't think it is 100% necessary, it is a good idea to do."Where's Stick man????????" - 7A749"SHHHHHH!! I sent him over to snag that MIC-4 while tbone wasn't looking!" - duaneb55"I have bought a few of Tbone's things unlike Stick-Man who helps himself" - TozziWelding"Stick-man"
Reply:Thanks for the responses. I read my welders manual again after posting and it says that if HF interference is a problem use the additional ground (my machine is a home unit, not run off a generator). HF has not been a problem for me I think because when I ran my power line, about mid point between the panel and outlet I installed a grounding stake, so any HF energy is grounded to earth before reaching the panel, rather than going through the panel to get to ground. Makes sense now.
Reply:I install grounding grids for tactical communications equipment. These types of grounds are not the easiest thing to get good enough to support equipment. Most often You have to drive rods in a configuration 9+ ft deep all tied together to get a sufficient ground. But then again our earth electrode subsystems have to take on acts of god.
Reply:Originally Posted by Stick-man Although, I don't think it is 100% necessary, it is a good idea to do.
Reply:I had the same question, especially when it concerns GFI circuits.  I work on a lot of marina repair.  It seems useless to use a GFI cord if nothing is grounded, I have tossed the cord in the lake to see if anything tripped, and it did not.  I'm not sure if a external ground to earth would make it all work or not.  We also have gen sets on our fire engines.  They are running electric flood lights and electric smoke fans for night structure fires. It has always worried me, especially since everything is wet.
Reply:Originally Posted by blackbartI had the same question, especially when it concerns GFI circuits.  I work on a lot of marina repair.  It seems useless to use a GFI cord if nothing is grounded, I have tossed the cord in the lake to see if anything tripped, and it did not.  I'm not sure if a external ground to earth would make it all work or not.  We also have gen sets on our fire engines.  They are running electric flood lights and electric smoke fans for night structure fires. It has always worried me, especially since everything is wet.
Reply:I'm going to assume the states is the same as us here in Australia,There are 2 types of electrical appliance wiring here, double insulated, and earthed.Double insulated basically means there is at least 2 levels of insulation between 240v and possible human contact.Earthed appliances have the chassis attached to ground. In normal operation, its really not that necessarily, but in a fault, where something touches the chassis, it gives the current somewhere to go. Otherwise, the device can sit there live, waiting for someone to touch it.also, in this day and age, if you have an RCD protection device, it will also cut out if it detects a certain amount of milliamps going to earth, thus saving you even better then just an earthed chassis.so, I'd say yes, its fairly important, safety wise.
Reply:Originally Posted by stiffmanI'm going to assume the states is the same as us here in Australia,There are 2 types of electrical appliance wiring here, double insulated, and earthed.Double insulated basically means there is at least 2 levels of insulation between 240v and possible human contact.Earthed appliances have the chassis attached to ground. In normal operation, its really not that necessarily, but in a fault, where something touches the chassis, it gives the current somewhere to go. Otherwise, the device can sit there live, waiting for someone to touch it.also, in this day and age, if you have an RCD protection device, it will also cut out if it detects a certain amount of milliamps going to earth, thus saving you even better then just an earthed chassis.so, I'd say yes, its fairly important, safety wise.
Reply:Grounds and fire fighting equipment is an issue. We had a fire at a neighbors house, out building hit by lightening and caught fire. Fire department responded to the night fire and started hoses working. They did not see the overhead 240 volt service to the shed from house. Fireman was knocked to the ground by shock and had to have EMT's respond to help him. I don't know what truck, hose fireman grounding would be needed to keep this from happening. Perhaps bonding wires incorporated in hoses to ground to fire hydrant, truck and then fire hoses.. What would be the safest way for this to work. This is a common instance and is there something that can be done to keep fireman safer from this type of shock happening. I know they won't start hosing a house until the meter is pulled but it's still a risk even then.
Reply:Originally Posted by Broccoli1It has no idea the current is going to Earth ground - it only knows that it is not going where it is supposed to go. The ground rod doesn't offer safety in a fault.
Reply:I'm not worried about a fireman getting shocked from a live wire, thats his or the chiefs fault.  I am worried about generated power from the fire engine running through extension cords through usually wet, flooded ground. I don't understand how a GFI works if it dosen't have a good ground. All I know is when I experiment with it, by throwing a device in the water, or a cord in the water, they never seem to trip.  I know I am taking this post off track, sorry about that.
Reply:As Ed explained above the name Ground Fault Circuit Interupter is very misleading. It works by looking at the power going out thru the hot and comparing it to the power returning thru the neutral. If there is any difference between them the circuitry in the GFCI shuts the power off. The ground is not involed in this at all.
Reply:So, how do I test it correctly to make sure my firefighters are safe? Because it seems to fail anything I throw at it. I have used a GFI at the origin and tried one at the end of the cord with no difference. I have also experimented with different generators.
Reply:The GFCI should be at the source not at the cord end. Using the test button is the best way to test them. They are not full proof devices by any means, you still need to use good judgement and avoid unsafe practices.
Reply:blackbart, my first thought would be for your firefighters to have electrically insulated gear. The stuf they make THHN wire has good elect insulation and a hi thermal breakdown. I think it has Teflon/Kevlar or ? Maybee your already using it.My second thought is about the water you use. Dirty water is conductive but pure H two O or di-Ionzed does not conduct electricity. When you add dirt, metal shavings grease, sweat or salt, to water it becomes conductive.  Salt NaCl should be added to you next xperiment of putting the xtension cord in the water. Salt is an Ion and will make a difference in the resistance of the water you use.
Reply:The test button works, although I have tried both ends of the cord.  Perhaps the water test isn't dirty enough.  Even though fire turnouts are insulated, they are usually soaked in a big fire.  We never had a problem, I just never understood how it did (or did not) work.
Reply:External GFCI testers put a small load from hot to ground (not neutral) to see if the GFCI can detect the leakage.  I've seen it said that some of the really old GFCIs would test OK with the test button but not actually function properly."USMCPOP" First-born son: KIA  Iraq 1/26/05Syncrowave 250 w/ Coolmate 3Dialarc 250, Idealarc 250SP-175 +Firepower TIG 160S (gave the TA 161 STL to the son)Lincwelder AC180C (1952)Victor & Smith O/A torchesMiller spot welder
Reply:One caveat to add. Not sure about your machines, but mine bonds earth ground to common. If you energize the main panel at the service entry of a house or building you can have two points in the wiring plant where earth ground and common are bonded. By code this should happen at the main panel and no other panel. The ground is engineered to handle and route any unexpected electrical energy to earth ground, for obvious safety reasons. If the ground is also bearing common lead current between two points, the ability of the ground to accomplish this can be degraded or defeated. Wiring failure is a possibility. This is the same sort of issue that is created when you wire a sub-panel and don't unbond the earth ground from common.
Reply:Originally Posted by blackbartI'm not worried about a fireman getting shocked from a live wire, thats his or the chiefs fault.  I am worried about generated power from the fire engine running through extension cords through usually wet, flooded ground. I don't understand how a GFI works if it dosen't have a good ground. All I know is when I experiment with it, by throwing a device in the water, or a cord in the water, they never seem to trip.  I know I am taking this post off track, sorry about that.
Reply:I just threw cords in while working on a marina, we did drop a live drill in accidentally with no tripping of the GFI either, so that would be the "device" I am wondering if there is any real protection provided by using a GFI cord. If you push the "test" button it would trip.
Reply:Dropping a cord or tool into water will not trip a GFI because, you've dropped both the hot and neutral into the water. The electricity naturally seeks the easiest path which is straight back to the neutral. Try dropping just the hot in and see what happens. They put GFI's on hair dryers for this scenario: Girl with wet hair uses hair dryer, wet hair accidentally enters rear of dryer, wet hair contacts brushes in fan motor, creates circuit to ground through girl, current from hot increases through new circuit, current increase creates differential between hot and neutral, GFI trips.Ian TannerKawasaki KX450 and many other fine tools