IMPEDANCE OF STRANDED STEEL CABLE

[mikesolo1]

We manufacture stranded cable of different materials to ASTM Standards that characterized our products in terms of physical and chemical properties, and leave their electrical properties up to system design users/customers. Now a customer wants to know the impedance rating of 3/8" and 1/2" 7-wire galvanized steel cable used as "Shield Wire" to protect power distribution networks from lightning strikes by conducting the energy to ground. Anyone know how I can determine this? I am not, and do not employ, an EE.

 

[charlie b]

The material property of interest is "resistivity." It is commonly annotated with the greek letter "rho," and is expressed in units of "ohm-meters." If you can provide that value, then the "resistance" of a length of the cable can be determined using the formula, R = rho times L divided by A, where R is the resistance, L is the length, and A is the cross-sectional area. If you cannot provide that value, then you cannot assist the customer with this request.

Please note that the customer asked for "impedance," not "resistance." Impedance is found by combining (using vector addition) resistance with "inductive reactance" and "capacitive reactance." Those later two things are not within the scope of the manufacturer of the cable to determine. They depend entirely on the geometry of the installation. The customer would have to bring an EE on board to figure the reactance values, and from that determine the impedance.

So just to satisfy my curiosity, can you provide a value for resistivity?