Lightning Isolation Effectiveness of PVC Conduit for bare Conductor

[cuky2000]

The author of the enclosed figure said:

The PVC pipe in Figure 1 insulates the surface soil from the lightning surge current, thereby reducing the step potential, a personnel safety hazard...

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I wonder how effective a PVC elbow could insulate and protect this installation from lightning surge or help reducing the step potential. Does this really provide significant protection or isolate anything?

Thanks for your comments.

 

[dpc]

I don't really think it is doing much. With lightning, you are dealing with an arc that just went about 30,000 feet through the air, so it difficult to see how a quarter inch of PVC is going to provide reliable isolation.

 

[alehman]

I think the physical protection it provides, reducing the likelihood of damage provides much greater value than any reduction in effectiveness (which there is none).

 

[jghrist]

There will be a large step potential with or without the PVC conduit. Step potential comes from current flowing through the soil causing a voltage drop. Most of the current will flow through the soil from the ground ring and rods, not from the down lead.

If anything, the conduit elbow will require extra bends in the down lead, increasing the impedance to the lightning surge and increasing the tower potential.

 

[waross]

If you are close enough to a tower to worry about touch potentials resulting from a lightning strike, your priotities may be a little askew.



"Doctor, was there any sign on the body of a touch potential shock?"
"Well the body is so badly burned by the lightning bolt that it is impossible to tell if there were any secondary shocks!"

If you are far enough from the tower to escape direct injury from the lightning strike, you will be far enough away from the ground rod that there will be no difference in the step potential. There is a lot of area connecting the surface soil to the subsurface soil. You won't get very far from the ground rod before the surface potential will be equal to the subsurface potential.

Bill
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"Why not the best?"
Jimmy Carter