Stainless Steel Earth (Ground) Bars - Conduction of Lightning current 2

[acog]

Hi All,

We have a project where we are free issued stainless steel earth (grounding) bars. The copper down-conductors from lightning terminals (in the air) are run to this earth bar, and all of the copper conductors which connect to earthing electrodes buried in the native soil are also connected to this earth bar.

If a lightning strike occurred, the current would travel down the copper down conductors and through the stainless steel earth bar, then through the copper tails to the electrodes in the soil.

I have heard from consultants on two occasions now that the stainless steel is ferrous and therefore does not conduct fast wave-front (high dV/dt) energy from lightning strikes.

Is this correct? Are there any papers or guidelines which back up this statement?

 

[jghrist]

Running lightning conductors through steel conduit will cause high impedance, similar to running a single phase conductor through steel conduit. There is no technical problem with using steel conductor, however. NFPA 780: Standard for the Installation of Lightning Protection Systems, 4.19.1, allows the metal framework of a structure to be used as the main conductor of a lightning protection system if it at least 3/16" thick. Section 4.6.4.2 allows stainless steel or galvanized steel overhead ground wires. 4.13.2.5, allows stainless steel ground rods. Section 4.2, however, requires the protection system itself (air terminals, conductors, etc.) to be made of copper or aluminum. I would say that there is no technical problem, but the stainless steel earth bar could be considered prohibited by Section 4.2.

 

[prc]

Electrical resistivity of stainless steel is 4-5 times more than that of mild steel or iron. Hence current conduction through stainless steel will result more voltage drop +heating.