On Mon, 17 Jul 2017 07:59:41 -0700, Jeff Liebermann wrote:

Not high enough. If you want to measure really high resistances, such
as insulation leakage, you need a Megger (which is actually the name of
the company that makes them but has become somewhat of a generic term
for high voltage resistance testers):
https://www.google.com/search?q=megger+meter&tbm=isch
If you want to see if you really have water in the coax cables, you need
one of these insulation testers.

Yeah, I have one. They can still be used perfectly servicably if they're
within spec. The people at Megger tell me that every so often, an old
hand-crank version from the 50s or 60s will come in for re-calibration!
The one I have is the 250V model which is relatively unusual here in the
UK as almost all of them here are 500V. We would typically use the 500V
version for testing our 240V domestic wiring. I guess the 250V model was
intended for export to countries which use 110/120V.

The current range of Meggers are quite expensive, IRO $1200 but at least
you don't have to crank them any more.