Hi
We have a 160A Reboot Mig Welder. Its only a cheap jobby off amazon and was brought to replace a broken Sealy super mig 140 but welds suprisingly good.
However we have encountered a problem when welding to a steel stair case. The staircase is welded to the main steel structure of the building. The problem we are facing is when welding to it we are buring out the earth cable on the supply side of the welder. I have checked continuty between the work return clamp and the welders case and is open as it should be, however when the return clamp is clamped to the staircase there is now continuty between them, basically sharing the same ground. This is resulting in 160A passing through the earth cable that has been measured with a clamp multi meter.
Disconect the return clamp from the staircase and try to weld some steel steel that is not connected to the building and there is zero continiuty between the work return and earth and measure zero amapage through the supply earth and can weld as normal. The problem only exists when welding to the buildings steel that is sharing the same earth, presumable bypassing the work return clamp.
Any ideas on how to fix this problem?
This doesn't make sense.
Have you checked continuity between the mains earth and the welders case and also continuity between the mains earth and the welding earth clamp ?
Like water, electricity will take the shortest route which should be straight back to the welder via the welding earth earth cable.
For the current to flow through the mains earth cable there must be an internal connection from the welding current earth side to the mains earth side.
If all 160A is flowing through to the mains earth cable then the welding earth cable must be carrying no current at all which would mean that its not connected to the welding earth...
If you can weld on an isolated piece of metal with the earth clamp connected then it must be connected internally to the welding side which contradicts the above.
What I think is happening is that the welding earth clamp is not actually connecting securely to the stair or that the section of stair you are connecting it to is isolated from earth and so the current is going back through the mains earth rather than the welding earth.
Realistically, it's bad practice to have any connection from the welding side to the power side so this shouldn't be happening.
This doesn't make sense.
Have you checked continuity between the mains earth and the welders case and also continuity between the mains earth and the welding earth clamp ?
Like water, electricity will take the shortest route which should be straight back to the welder via the welding earth earth cable.
For the current to flow through the mains earth cable there must be an internal connection from the welding current earth side to the mains earth side.
If all 160A is flowing through to the mains earth cable then the welding earth cable must be carrying no current at all which would mean that its not connected to the welding earth...
If you can weld on an isolated piece of metal with the earth clamp connected then it must be connected internally to the welding side which contradicts the above.
What I think is happening is that the welding earth clamp is not actually connecting securely to the stair or that the section of stair you are connecting it to is isolated from earth and so the current is going back through the mains earth rather than the welding earth.
Realistically, it's bad practice to have any connection from the welding side to the power side so this shouldn't be happening.
its like your welder return lead is not connected to the steel
There are several scenarios where welding current can pass through a building's mains Earth wiring but, perhaps because I lack imagination, I cannot think of a scenario where welding current would pass through the welding machine's mains lead Earth.
That scenario would require the welding circuit to be connected to mains Earth within the welding machine - a fault - or for the frame ground of the welding machine to be independently connected to mains Earth.
I have checked continuty between the work return clamp and the welders case and is open as it should be, however when the return clamp is clamped to the staircase there is now continuty between them, basically sharing the same ground. This is resulting in 160A passing through the earth cable that has been measured with a clamp multi meter.
That is normal and should not, by itself, cause welding current to flow in the mains Earth.
What I think is happening is that the welding earth clamp is not actually connecting securely to the stair or that the section of stair you are connecting it to is isolated from earth and so the current is going back through the mains earth rather than the welding earth.
I think that would result in welding current in the building Earth wiring but not in the welding machine's Earth wire (in the power lead).
I'll have to think some more.
Jack
make sure the welder outer case is not touching the workpiece , if the welding cable clamp is not making good electrical contact too. you then have the perfect scenario for the full welding current to travel along the mains earth frying the insulation and trashing the mains wiring usualy till it trips due to a full on short .
seen it chain block chains glowing red hot as several welders blissfully unaware of it
as there earths were located on another section but some one has moved it. best practice is to keep the earth lead near the weld if practicable
make sure the welder outer case is not touching the workpiece , if the welding cable clamp is not making good electrical contact too. you then have the perfect scenario for the full welding current to travel along the mains earth frying the insulation and trashing the mains wiring usualy till it trips due to a full on short .
I still can't see it. That would assume a connection between mains Earth and and welding "ground" internal to the welding machine.
I'm not saying that the problem can't happen, just that I can't see it. Can someone sketch the Earth loop?
Thanks
Jack
I still can't see it. That would assume a connection between mains Earth and and welding "ground" internal to the welding machine.
I'm not saying that the problem can't happen, just that I can't see it. Can someone sketch the Earth loop?
Thanks
Jack
The outputs are not floating the negative is grounded
The current leaves the gun, goes through the steelwork to the main bond at the MET then through the earth leading to the welder to the secondary coil negative leg, thus completing the circuit
The outputs are not floating the negative is grounded
The current leaves the gun, goes through the steelwork to the main bond at the MET then through the earth leading to the welder to the secondary coil negative leg, thus completing the circuit
Thanks but the negative is grounded
external to the machine. For welding current to flow in the power cord Earth, the negative has to be grounded inside the machine.
After some thought, I see how there is potential for welding current in the power cord Earth.
In the above scenario, there is no loop via the power cord Earth.
In this scenario, there is an Earth loop but it is external to the welding machine.
If the case of the welding machine being in contact with the stairs or the steel building frame,
Then there is potential for a small current in the mains cable Earth. The primary path would be from building to the bottom of the stairs - except, if mains Earth were bonded to the building frame in the vicinity of the stairs.
So, I got there in the end but I think you'd have to be pretty accident prone to encounter the problem. Perhaps the OP should buy a lottery ticket - or a welding machine with rubber feet.
Thanks for your patience
Jack
Thanks but the negative is grounded external to the machine. For welding current to flow in the power cord Earth, the negative has to be grounded inside the machine.
After some thought, I see how there is potential for welding current in the power cord Earth.
View attachment
In the above scenario, there is no loop via the power cord Earth.
View attachment
In this scenario, there is an Earth loop but it is external to the welding machine.
If the case of the welding machine being in contact with the stairs or the steel building frame,
View attachment
Then there is potential for a small current in the mains cable Earth. The primary path would be from building to the bottom of the stairs - except, if mains Earth were bonded to the building frame in the vicinity of the stairs.
So, I got there in the end but I think you'd have to be pretty accident prone to encounter the problem. Perhaps the OP should buy a lottery ticket - or a welding machine with rubber feet.
Thanks for your patience
Jack
No on transformer machines it's not uncommon to find the earth connected to one side of the transformer
No on transformer machines it's not uncommon to find the earth connected to one side of the transformer
Is that mains Earth connected to the secondary? Or do you mean one of the DC welding terminals is connected to mains Earth?
Can't change polarity then. Do you have an example? I've only had a couple of transformer MIGs and their outputs were floating.
Thanks
Jack
I know you have tested between the welder earth clamp and welder case and found it is open (correct/as it should be)
but have you tested resistance between the
earth pin on the plug to the
welder earth clamp? / (& also earth pin to welder case)
You may have assumed the earth pin is connected to the case, (which it should be) but it may not be - and if not it may be somehow connecting with the earth clamp side of the welder?
Sorry to resurrect but wanted to explain the scenario here as there is a lot of misunderstanding in the thread.
The OPs welder is a gasless inverter mig. It sounds likely that it's a non isolated inverter circuit as shown below and the neutral is wired directly to the 'negative'
Being gasless the earth clamp is connected to the 'positive'. So when you clamp the earthed staircase the current runs to earth. These designs can be dangerous as when IGBTs fail they often fail short circuit and you have 220v on the tip. Now an RCD should shut that off in a couple of milliseconds so I'd wonder what state the wiring is in.