Consequences of electrically bonding SST to carbon steel

[rjohnston]

Here is the scenario:

1. Two large carbon steel stuctures are submerged in pool water.

2. The structures are coated with an epoxy paint coating.

3. The structures are joined together by SST pins.

4. The pins are electrically isolated from the carbon steel structures by non-metallic bushings.

5. The pins are over 4" long.

If the structures were electrically bonded by a cable running from structure 1 to the pin and from the pin to structure 2, what would happen?

Thanks

 

[PVRV]

Consider what is required for galvanic corrosion to occur and then review the galvanic series.

Note: Surface Area
Couplings/Joints
Water Content

 

[Boomerang]

rjohnston

What material is your cable made of?
Is it structural or electrical cable?
Does it have to be in electrical contact?

 

[rjohnston]

Boomerang,

The cable is a braided flexible grounding/bonding cable (I think it is tin plated copper)

What I am fighting with is NEC article 680.26 There is a section that states parts in a pool greater than 4" in any direction must be grounded.

What is your interpretation of this?

 

[Boomerang]

It reminds me of an article I read about a French LTA craft. During its construction and before it was allowed permission to take off it had to comply with safety regulations that demanded hand-rails. The hand rails were duly installed to spec and the craft was no longer LTA.
Were the regulations wrong? No, and they guaranteed that craft was doomed never to get off the ground.
I understand regulations require your project must have a common earth.
You might consider installing zinc blocks near each end of the cable. Connect each block electrically parallel to the cable. Leave the ends of the cable free to connect as specified to the steel structures.
Provided all the zinc parts are submerged it would seem to satisfy the corrosion issue arising from the earthing requirement.

 

[rnd2]

rjohnston

Well, it seems to me that the sst pins are submerged and the cable is connected to the carbon steel structure above and clear of the water and the all of the carbon steel structure below water is electrically isolated with a protective surface treatment, then there is no opportunity for galvanic corrosion to occur between the sst pins and the main structure. The only opportunity would be between that part of the copper cable that was underwater and the sst pins it connects to.

 

[rjohnston]

rnd2

Everything is submerged. 24hrs a day, 365 days a year.