Larry and group,
On the surface, the flex conduit ("greenfield") sounds like a good
solution, but there are problems. As mentioned in another reply, the stuff
is not recommended in wet or corrosive environments. The armor, whether
steel or aluminum, will corrode. The result is insulation between the
turns of the armor. This leaves a rather long conductor for a ground, and,
if steel, a poor one at that. Flexible conduit is not recommended for use
in barns, for instance, since the corrosion can produce such a poor ground
that the helical armor can no longer be relied upon to have low enough
resistance to blow the fuse or trip a circuit breaker in event of a ground
fault. Instead the armor carries the fault current, and having resistance,
can heat sufficiently to cause a fire.
I wouldn't count on the armor to provide a good shield or ground over the
long term.
As for EMT, the difference is in the connectors and fittings you use. They
are available in "compression" (with a big nut that surrounds the tubing
that one tightens with a wrench) and "set screw" (which has one or more
screws that one tightens upon the tubing with a screwdriver). Of the two,
"set screw" provides the best continuity of ground, as the screw bites into
the tubing. "Compression" connectors grip the tubing over a wider area,
but without such a high pressure point as the "set screw".
EMT would be OK, but only if you use "set screw" fittings.
Hope this helps.
>From a professional electrician with 25 years in the business...
73, Chris, kd3oa@ptd.net
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