Bridge Bonding

[dmott]

I work for a Civil Engineering firm in Ohio and we are the CM on a bridge under construction. The bridge uses steel beams and is located under a 138 kV transmission line, crossing it at roughly a 45 degree angle. The beams sit on an elastomeric bushing, isolating them somewhat from the bridge piers, which are steel reinforced concrete.

Question: Is there any Code requirement or is there an engineering good practice that would require the bridge steel to be bonded and grounded due to the veritcal proximity (~35 feet I am told) to the high voltage transmission lines?

Thanks to anyone who can help.

 

[dereckbc]

Re: Bridge Bonding

This is outside the scope of the NEC. I suspect that a bridge is going to be firmly anchored by concrete peers, which will have abundant re-enforcing steel embedded in the concrete footings. I would look into a Ufer ground system that uses the concrete peers as a ground electrode and specifying the bridge steel members bonded to the concrete re-enforcement rebar.

 

[tom baker]

Re: Bridge Bonding

I have heard of an application of traffic signal poles and mast arms under a 112 KV line where the traffic signal poles developed a static charge. The solution was a grounding grid or a ufer ground. The bridge could be "likely to become energized" but thats a stretch. The answer to your question may be more in the NESC as it is a power transmission line issue.

 

[bennie]

Re: Bridge Bonding

Tom: Put a CT on the leg of an iron maiden and read the current flow. Spooky!