Continuing Thread: Steel Structure Grounding/Bonding

[lbnuke]

This is intended to add to the Steel Structure Grounding thread here: http://forums.mikeholt.com/showthread.php?t=106239. The original thread has been closed.

When steel structures utilize structural steel for the path to ground (i.e. grounding electrical equipment to columns at each level, then perhaps corner columns at the ground level), how is electrical continuity maintained between the structural components in the ground path? Does a weld create an electrically continuous connection? Does a bolted connection? Does a bolted connection with a piercing washer? In order to maintain electrical continuity, paint and other non-conductive coatings must be removed per NEC 250.12. How is painted steel modified or pierced to electrically connect two separate steel members when delivered to site then painted in the field prior or post erection? Does steel typically arrive primed, stock, etc.?

 

[ActionDave]

Welcome to the forum

This is intended to add to the Steel Structure Grounding thread here: http://forums.mikeholt.com/showthread.php?t=106239. The original thread has been closed.

When steel structures utilize structural steel for the path to ground (i.e. grounding electrical equipment to columns at each level, then perhaps corner columns at the ground level), how is electrical continuity maintained between the structural components in the ground path?

Faith. Other than that there is usually a page of specs somewhere.

Does a weld create an electrically continuous connection?

Yes.

Does a bolted connection? Does a bolted connection with a piercing washer?

Yes.

In order to maintain electrical continuity, paint and other non-conductive coatings must be removed per NEC 250.12. How is painted steel modified or pierced to electrically connect two separate steel members when delivered to site then painted in the field prior or post erection? Does steel typically arrive primed, stock, etc.?

The primer on most building steel is not anything I have seen anybody worry about. If there is actual paint, as in a layer that can be measured even if it is less thick than a business card, then a grinder or a helper with an old screwdriver can be used to scape it off.

 

[don_resqcapt19]

I think the question is about the steel to steel connections that are made by the iron workers, and for bolted connections, they will not be taking the paint off. The also will not be using piercing washer to make the structural connection. Their job it build a structure that will deify gravity, and they are not concerned about the electrical conductivity of the structural steel joints.

I expect that enough of the paint or coating is damaged in the process of installing the steel so as to have a conductive joint, but given the steel is not being used as an equipment grounding conductor I don't see a real world issue here.

 

[augie47]

Does make one wonder though when you have a steel frame building and you install with service grounding electrode and UFER at one end and then
300 ft away you bond your incoming metallic water to the steel.

 

[starbolin]

I'll answer you question with a question: What is the breakdown voltage of the contact between two, loaded, unmachined, bolted, torqued, 6 inch sq. steel plates with only a 1 mil paint coating between them?

Building steel is only required to be an 'effective ground-fault current path'. This may be a lesser requirement than your hypothetical 'continuous electrical connection'.

The onus falls on the installer to verify the effectiveness of any ground-fault path he creates. 250.4(A)(4)

 

[don_resqcapt19]

Does make one wonder though when you have a steel frame building and you install with service grounding electrode and UFER at one end and then
300 ft away you bond your incoming metallic water to the steel.

It doesn't make me wonder too much. I mean you can drive two ground rods (assuming no other existing electrodes) and connect them to the service grounded conductor with a #6 and call it good.

 

[don_resqcapt19]

...
Building steel is only required to be an 'effective ground-fault current path'. This may be a lesser requirement than your hypothetical 'continuous electrical connection'. ...

What code section permits using the building steel as a ground fault current path(EGC)?

The code permitted interconnection permits using the steel as a grounding electrode conductor and not as an EGC.

 

[ActionDave]

given the steel is not being used as an equipment grounding conductor I don't see a real world issue here.

I agree.

 

[jaggedben]

Does make one wonder though when you have a steel frame building and you install with service grounding electrode and UFER at one end and then
300 ft away you bond your incoming metallic water to the steel.

Around here I think that would be a fail.

As for wondering about it, this is something where you can relatively easily measure the ohms and get an idea of how bad it is.
I would guess that bolted steel structures tend to have many, many bolts that would create multiple redundant bonding pathways even if any given nut or bolt had some paint limiting the size of the connection.

 

[iwire]

Around here I think that would be a fail.

It should not be, the NEC allows it and it has saved time and materiel on jobs I have run.