Bonding of Steel Welding Bench

[ballyv]

Hi all,

I am looking for some guidance on the bonding of Steel Welding benchs for a training facility with 10 such benches. The benches were previously bonded using a 2.5mm PE back to the main earth node. A trainee then subsequently went arc welding without attaching the welder earth clamp directly to the table but must have connected it to some other steel structural column which was bonded. This resulted in the return path for the welder current running through a section of the 2.5mm PE and destroying it.
I cannot find anything specific regarding european regulations regarding bonding of welding benches as as such I am unsure whether it is neccessary or not. If it is neccessary then is the use of Earth Continuity Monitors or alternatives required to protect the PE?

Any help appreciated.

 

[roydm]

That's a good question, I wish I knew.
I used to work in a shop that made railway wagons, the welders were attached to the rails.
This was fine with the old white metal bearings but when we changed over to roller bearings
it caused a few failures before we realized the problem.

 

[mcgyvr]

Yes interesting question.. I think the answer will depend on the type/isolation of the welders you have.
I'd think the best/generic answer would be to not bond the benches and to ensure its isolated and to enforce proper protective equipment like rubber shoes,etc...

 

[GTstartup]

Seems like you should make the earth cable gage the same as the welding cable

 

[mcgyvr]

Yes if you do decide that bonding is what you want I would ensure that the cable and ANYTHING that would/could carry the welding current is sized accordingly. But be very careful.
There are numerous stories about someone just grounding to building steel and carrying just the stinger around causing multiple failures/issues in the whole building.

This is really why I think NOT bonding is a better solution for most cases.

 

[MiketheEngineer]

I was always taught to bond to the object being welded. If not possible - there can always be a problem or two...worst being that you kill yourself.

 

[PersonalProfile]

Far from an expert, though my interpretation of AS3000 (AU standard for EIC installations) requires the bonding to carry fault currents (i.e. it should be at least as large as the normal conductors), ref:

http://www.wiringrules.standards.org.au/LinkClick.aspx?fileticket=r0eaWYWK0Kc=&tabid=380

Question 010/2009.

Regards,
Lyle

 

[Compositepro]

Equipment bonding is not required to carry welding current. When a welder applies the ground clamp to an object he has full responsibility to fully understand what is in the weld current path. Equipment bonding conductors are not normally supposed to carry any current.

 

[MikeHalloran]

>>> A trainee then subsequently went arc welding without attaching the welder earth clamp directly to the table<<<

End of training.
Next candidate, please.


Mike Halloran
Pembroke Pines, FL, USA

 

[ballyv]

I'm not sure if increasing the guage of the earth conductor is the answer as to take this option to its natural conclusion you would have to size the earth conductor to take the full load current of any equipment being used on-site. As the welder is a transformer of sorts and the voltage in the secondary winding is less than the primary, then the current will be greater in the secondary. This is why the standard protection using an RCD will not be effective- The live and neutral in the primary remain balanced even when the welder is using the PE as the return path.
This is the reason why I am looking into Earth Continuity Monitors but with no success as of yet.
Thanks for all the feedback so far

 

[biff44]

Well, it sounds to me that from experience you will need 00 welding cable bonded to each table, earth, AND the building frame in order to survive next semester's onslaught.

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[biff44]

I thought on it some more, and now am not so sure if earth grounding is a good or bad idea. In some cases it might make electrocution more likely. But on the other hand, if you are going to attach one welding clamp to a bench, and free hand the other, then you already have that potential electrocution risk.

I called up Miller, and they recommened a good earth ground IF you are using high frequency TIG welding. Did not have an opinion on other types of welding.

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting