Bonding Copper to Galvanized Steel

[Kiribanda]

Gentlemen,

I have a question on bonding copper to galvanized steel.

In all electrical outdoor substations, usually the ground grid buried is COPPER. The substation fence is usually HOT DIP GALVANIZED STEEL. Normally this fence is bonded to the grid using thick COPPER wire to avoid any shock hazards on the fence. In addition to above, the same fence is also in contact with the grid through the SOIL (electrolyte).

1) Does the above setup make a corrosion cell?

2) Is there a possiblity for the fence (nobel material) get corroded and destroy after sometime?

3) How to avoid this?

Your input is appreciated.

 

[unclesyd]

From what I've seen under similar conditions the HDG wire will expire prior to any problems with electrolysis. Our site is surrounded by by HDG fence and is bonded to the site grounding grid in numerous places. I may stand corrected but I think this was done due to the potential of lightening strikes. The power company has 3 large high voltage substations on site and all are surrounded by HDG chain link fence which I know has been in place since the early 60's. It to is bonded to our grid.
On all the fencing on site the post are encased in concrete.
All the fencing has a bottom taught wire which is where we usually look for any problems. The only problem is that part of the fence is painted with ZRC every so often due to industrial atmospheric corrosion. The ground wires were originally attached with CadWeld at about 6" but the later ones were clamped at the same height.

 

[CoryPad]

1) Yes, you have dissimilar metals in contact with the possibility of electrolyte (e.g. rain).

2) The fence is not noble compared to the copper wire - the zinc will be sacrificial to both iron and copper. The zinc coating will corrode over time due to normal atmospheric corrosion, but it may be enhanced locally due to contact with the copper.

3) Probably not necessary, unless you are near a coast and have a highly saline atmosphere.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Metcorr]

1. As Corypad has said, you have a potential galvanic cell. The common electrolyte is possible through rain or moisture. However, it may not be much of a concern if rain is occasional.

Regards,
MetCorr