Tom wrote
> The fact that a shield is steel or iron or not doesn't make
> a bit of difference for energy above a few Hz, except it
> might actually make it a poorer shield from increased
> resistance.
The magnetic field is this case is an external agent caused by a huge
current source, in the transformer we have the magnetic current inside the
iron. We use it to transport energy. It is not the same case; here we want
to avoid an external magnetic field to induce current on wires inside the
conduit pipe. Resistance is good to reduce the energy. That's why we have
iron conduit in professional inhalations.
Copper or aluminum does not protect your cables during a lighting strike
close buy. I had a tower in Brazil with 120 ft high, all cable running
inside a 2" galvanized water pipe. That tower used to get hit 8 -10 times a
year, every year. I never had any equipment damaged by lightning.
Regards
Carlos
N4IS
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