Electrical Grounding: Not Like This

 Corroded Grounding Strap - Walkway Over the Hudson

Corroded Grounding Strap – Walkway Over the Hudson

Spotted this through the railing on the north side of the Walkway Over the Hudson:

I’m not sure what it’s bonding to the bridge structure, but the corrosion where the braid touches the I-beam suggests an electrical potential drives the reaction. There’s stout bonding braid connecting all the railing sections together, but this braid wanders off below the decking and seems too casual / flimsy for lightning protection.

The rivets date back to the late 1800s. I suspect that bolt won’t last nearly as long…

About these ads
  1. #1 by Robert on 23-November-2012 - 00:50

    Ed, that does not look right for normal grounding. It may be a “cathodic protection” setup, but I cannot say. Got any more shots of any ground straps and what they attach to?

    • #2 by Ed on 23-November-2012 - 12:37

      any more shots of any ground straps and what they attach to?

      The ones connecting the railing segments look similar to that, although the ones I saw have formal lugs and less exposed thread.

      A guy managed to heave himself over the edge a few months ago (hitting the Hudson from 200 feet up isn’t survivable), so they’re a bit twitchy about people leaning over / through the railing. We’re usually on our bikes and can’t see the infrastructure; I’ll (try to) remember to go for a walk mid-span the next time we’re there. There’s no way to see under the decking from atop it, though.

  2. #3 by david on 23-November-2012 - 06:30

    How can there be any potential difference to drive corrosion along the edge when the end of the braid is clearly bonded to the girder two inches away? Wouldn’t it make more sense that the abrasion rubbing against the edge is responsible either directly or by disrupting coating (tinned? oxide layer?)? Or am I totally nuts here?

    • #4 by Robert on 23-November-2012 - 10:28

      Yes David, looks like contamination to me. The ground loop should have had slack in it to prevent abrasion. That braid is for a protected environment, not out in the weather. Should be insulated.

    • #5 by Ed on 23-November-2012 - 12:33

      How can there be any potential difference

      The two conductors first touch right at that nasty edge, so that’s where at least a little of the current flows…

      The abrasion definitely counts for something, because the braid has shined up the edge of the beam inward from its current position. Perhaps that nicks the coating, exposes the steel, and away it goes?