Welder Shock

[blacy]

Hello all. This is my first post here. I've been reading through the archives and have found you all to be very informative. Thanks for the discussions.

On to my question...

I work in a very old factory (built circa 1930). The electrical system is an ungrounded delta. We have an unsophisticated ground-fault detection system (3 lamps), but from what I've been told, they are only connected to the older part of the building. I'm not sure this is a true statement because we only have one power source from the utility into the main distribution building. From that main disconnect panel, we have several breakers feeding the older building, and only one feeding the newer building. There are no isolation transformers.

In the newer building we have had several people receive quite a jolt when they touched a welder with one hand and a piece of equipment steel with the other. The welders are wired for single phase 480V. The welders do not have to be turned on for the shock to occur.

Can anyone tell me what is causing this and what I could do to prevent it?

 

[charlie b]

My questions:
(1) Does this happen with only one welder, with more than one, or with all of them?

(2) Is (are) the welder(s) isolated from the floor and from any contact with a grounded surface? Are they portable and sitting on rubber wheels, for instance?

(3) What part of the welder gives the shock (case, cable, rod, etc.)?

(4) Have you tried to take a voltage reading between the welder and nearby equipment steel?

 

[jim dungar]

Remember bonding and grounding are two different things. You need to look how your different buildings are connected to earth and how they are connected together.

I suggest you get a reference book like "SOARES Book of Grounding and Bonding". It does a good job of explaining the different terms and concepts.

 

[pfalcon]

In the newer building we have had several people receive quite a jolt when they touched a welder with one hand and a piece of equipment steel with the other. The welders are wired for single phase 480V. The welders do not have to be turned on for the shock to occur.

Can anyone tell me what is causing this and what I could do to prevent it?

Without proper grounding in a factory the building steel and metal housings containing electrical components, such as your welder, will float to different voltage potentials. For example, if we presume that the earth below the factory is 0 volts then the building steel will act as an inefficient ground rod. The column has a resistance to the ground, probably greater than 25 ohms under a factory, and can therefore hold quite a voltage potential by induction from circuits nearby. Touch a piece of equipment that is grounded properly at the same time and you can become the conduit to drain the charge from the steel. You can also get this shock by touching virtually any metallic object in a factory.

Start simply by using your meters to check the voltage potential between different building columns. Also check the voltage potential between metallic objects and the building columns. Something in you facility is not properly bonded to the building ground. It may be the building steel itself.

 

[blacy]

Welder Details

Welder Details

charlie b -

This has happened to several welders when they are plugged into the welder receptacles in the newer building (by newer I mean built in the 1970's versus the 1930's). We even sent the welders out to be serviced and found no issues with them. We purchased a new welder and have the same issue.

The welders are portable with rubber feet.

The shock comes from the welder case.

I haven't taken and voltage readings.

jim dungar and pfalcon -

I understand grounding and bonding. The electrical system is not grounded. The equipment should be bonded, but I cannot guarantee that it is.

Also, this has happened at more than one welding receptacle in more than one area of the newer building.

 

[haskindm]

Remember that an ungrounded system is stil grounded! See 250.4(B).

 

[coulter]

Remember that an ungrounded system is stil grounded! See 250.4(B).

Could you get a little more specific? You really lost me on this one.

edited to add: Yes, I read all of 250.4.B

carl

 

[don_resqcapt19]

Have you checked the wiring at the receptacles? I have seen cases where the recps were wired with a hot phase connected to the grounding pin. We really need to see the voltage readings, and they need to be taken with something other than a high input impedance meter.
Don

 

[LarryFine]

Whether the supply is grounded or not, the building steel and the welder case should be effectively bonded via the EGC/GEC system.

 

[pfalcon]

... We even sent the welders out to be serviced and found no issues with them. We purchased a new welder and have the same issue...

I understand grounding and bonding. The electrical system is not grounded. The equipment should be bonded, but I cannot guarantee that it is.

Also, this has happened at more than one welding receptacle in more than one area of the newer building.

Ungrounded Delta was at one time the way of the factory. High Impedence Wye has replaced it in most cases. Both work the same on the floor. The overhead buss runs carry only the phases to the floor. Grounds are then all tied to the building steel. The building steel is all tied together to create an effective grounding grid.

Your welding power circuit must have a ground connection. This ground must be bonded to the building steel. All the building steel must be bonded together. If there is voltage present between the welding case and the building steel then somebody failed to bond everything. As OSHA would say you are looking at the possibility of "serious injury or death".

Take the readings to verify the bonding was not done correctly. The information you provided pretty well defines that. In several sections of our building we had to weld conductors to establish our grounding grid.

 

[Mustangx3]

Have you checked the wiring at the receptacles? I have seen cases where the recps were wired with a hot phase connected to the grounding pin. We really need to see the voltage readings, and they need to be taken with something other than a high input impedance meter.
Don

We see this A WHOLE BUNCH, the wires are usually hooked up wrong on 3 phase units when they are installed with a hot leg on ground.