Originally Posted by Zoidberg
Concrete is actually a pretty good current path (in the long term), particularly if it is reinforced (metal rebar), and particularly if it hasn't completely set as yet.
I'm guessing that the concrete in my foundation is pretty well set over these last 16 years.
- It is said that concrete in the Hoover dam won't be completely set for more than 100 years. -
Concrete can conduct if it has a high moisture content since it is somewhat porus, but that
moisture needs to have minerals in it, so moisture from the "swamped" air isn't going to cut it.
If I had a water leak by, say, overwatering plants near the outside wall, that might provide some moisture
that might provide some current flow, but remember we are talking millivolts and microvolts to create corrosion.
In a dry concrete slab, that's not going to happen unless there is rebar in direct contact with a duct.
This is evidenced by the condition of the ducts over all this time.
Dry and set concrete is effectively an insulator. If you look at lists of conductors and insulators, you'll find
concrete listed as the worst
in the list of conductors. This is lumping all concrete and all voltages together.
If the house gets hit by lightning with a jillion volts, the slab will certainly provide a nice path to ground.