[TowerTalk] iron pipe "lightning chokes"

[Jim Jarvis]

In response to the discussion about routing cables through
iron pipe...

k9yc wrote:
 
.I am QUITE certain that any smart engineer would specify that the 
.ground conductor be bonded to ferrous conduit at each end. Why?  
.Because it it was not bonded, the conduit WOULD significantly 
.increase the inductance of the ground wire running through it. But 
.by bonding it at both ends, the bonding conductor consists of the 
.parallel combination of the copper wire inside it and the conduit 
.itself. At low frequencies, the copper may contribute significantly 
.to the conductance. As frequency increases, the current will flow 
.almost entirely in the conduit. 

The sense I had was the opposite.  The iron pipe would present an 
inductance, which would tend to prevent strike current
from flowing along the outside of the cables.  There might be arcing
to ground or to cables....but the current would tend to seek lower
impedance paths, instead of proceeding into the building.  


n2ea
jimjarvis at ieee.org