Lightning Rods

[dik]

We have a 'Dead End' structure that has air terminals (lightning rods) secured to it.

The dead end structure is hot dipped galvanised and the air terminals come in aluminum, stainless steel, bronze and tin plate. The exposure will be exterior with intermittent wetting in an airborne chloride salt environment. Aluminum cannot be used for corrosion reasons.

What is the best means of connecting the air terminal to the dead end structure to minimise galvanic corrosion. The air terminal base comes in aluminum, bronze or tin plate. The base has a grounding conductor clamp.

Thanks, Dik

 

[EEJaime]

dik,

Well if you get the base and terminals in like metals, (bronze), or with stainless terminals, you will not need to worry about galvanic corrosion. And if you were to make your connections to your downlead conductor with like metals, (bronze-copper), or with exothermic welds, (Cadweld copper downlead?), you should not have any problems.

This "Dead End" structure is the dead end of an overhead distrubution network?

Regards,
EEJaime

 

[dik]

The dead end structure is like an A frame structure that accepts the 138 kV line from the utility and then connects to the customer's 138 kV line to the terminal building. The A frame structure is HDG and the air terminal bases are of either bronze, or tin plate. It is these two materials that will be in contact with the HDG steel... It is possible to provide a coating system to protect the bases or the fasteners. I was wondering how this was normally accomplished.

Dik

 

[Kiribanda]

dik,
Was it not possible to order the HDG A-frame with HDG lightning air terminals?

 

[jghrist]

Normally, we don't get fancy with air terminals for deadend structures and just put a galvanized steel pipe on top with a height that shields the bus and equipment. It is not really necessary to run a ground wire to the pipe because the structure itself is an adequate down conductor. Sometimes it is done, however, and generally copper conductor is used.

NFPA 780-2000, Standard for the Installation of Lightning Protection Systems, ¶4.4 says that metal towers constructed to receive a lightning stroke without damage require only bonding to ground terminals.

There is a potential for galvanic corrosion between the galvanized steel and the copper wire, with the zinc coating being sacrificial. Not normally a problem, but tin coating the copper will reduce corrosion if it is a concern.

The structure itself most likely is connected to the substation ground grid, probably with copper wire.

Short answer - tin plate is best.