EXPOSED METAL STRUCTURE BONDING/GROUNDING

[burchie]

Greetings,
I have a metal structure being built and it will come in three sections. the outer two sections will be completely built and welded where as the middle members (6 tubes) will be added at location. The tubes are painted and will be fit together with bolts. I have to ground/bond this for a chemical plant and it will house tanks of gasoline.

Since the bolts are painted and the steel tubing is painted I though I would have to add 12 bonds (6 on each side) to make the structure continuous and then ground to the grounding system.
Please tell me if I can get away with less than 12 jumpers and be secure.


In the drawing, you will see two separate sections and then a single section of tubing that will be bolted to the other two side sections. All members will be painted prior to shipment

 

[Dennis Alwon]

Is the paint conductive? If not you could have them belt sand around that area so the pieces are making contact. I don't think the screws themselves would need to be sanded.

 

[don_resqcapt19]

Dennis,
Are you suggesting that we would have to do that when we are bonding structural steel as required by 250.104? The building steel is often pre-painted and connected with bolts and nuts.

 

[petersonra]

I can't think of a good reason why the bolts holding the thing together could not serve to bond it as well.

 

[Smart $]

There are really no specific "requirements" how to handle this. It falls back on requirement that grounding be effective and ensured. Don hints that most do not typically bond around these joints. Using bolts, which are specified as proper bonding means, we reasonably assume these joints are not loosely connected enough to require bonding around. There is no prescribed means to test effectiveness, or exactly how to ensure.

I likely would only bond at the closest point to the electrical supply entrance. If there is doubt in the OP'ers mind, I recommend running a bonding jumper to each pre-assembled section. If still in doubt, proceed as required to alleviate one's fears. :blink:

A means to ensure without using bonding jumpers is to tack weld the bolted-together parts after assembly.