On Sat, 23 Dec 2017 23:53:36 -0500, micky
wrote:

In alt.home.repair, on Sat, 23 Dec 2017 23:14:03 GMT, Iggy
om wrote:

replying to trader_4, Iggy wrote:
You're absolutely right IF it's actually flexible conduit for just in the
crawlspace. However, If the entire place is actually BX, then the jacket can
be very successfully used as a ground conductor between a grounding outlet and
a grounding rod. I've done it and have had it done, the ground will be fully
confirmed by any and all Wiring Testers, GFCI Affirmers and other testing
methods.

Sure, a separate ground wire MAY be better, but only due to matched or
slightly better impedance

Is there any relevance to "matched" impedance when dealing with house
current? If it matched, what would it match?

Are you thinking about electronics, not electricity? Like matching
output transformer impedance to speaker impedance.

In fact, what is the point of using the word impedance? Aren't we
talking about plain old resistance, with no capacitative or inductive
component?


This is more of a theoretical problem than a demonstrated one but the
thought is that the extra impedance caused by the spiral wraps in the
cable armor might prevent the over current device from operating in a
fault condition. I suppose if the cable was long enough it could be a
problem tho. The "fix" in AC cable was just a thin strip of the armor
material that is actually scrap resulting from the manufacturing
process run along with the conductors that effectively shorts out the
"choke" created by the armor.
The reality is, in 2000, when I tested an old BX job built during
WWII, the cable armor still presented less than an ohm if impedance
at every receptacle in the building. (Using an Ecos ground impedance
tester)
To create this "choke" you would need each revolution of the armor to
be insulated from the one next to it.
Where this is more likely to cause a problem is with point of use
surge protectors that require the ground to be effective. The very
short duration transients will have trouble being shunted out, even
with a fairly low impedance in the armor.