[HCARC] Volt Ohm Meter - How to measure to check a ground

[Kerry Sandstrom]

Gary,

As I recall, when we used to work on sensitive components, we had a 
conductive (carbon loaded rubber?) mat on the bench and the wrist strap 
connected to a pin on the mat.  We also used copper covered benches, but I 
don't think that was for static but for a ground plane for RF measurements. 
I don't recall any tie into a building ground.  What you should be concerned 
about is a static charge that builds up between you and the rig and/or 
component.  That is why you want the equipment on a conductive mat with your 
wrist strap tied to the mat.  I secondary concern is the emi generated by a 
static discharge that doesn't involve the component/rig.  Sometimes enough 
energy will be radiated to couple in to sensitive components and cause 
damage.  I would wear non-synthetic clothing, probably cotton and I would be 
real careful what I had on my feet.  Naturally, I wouldn't have any power on 
the mat.

In NM we had a lot bigger static problem as our humidity was often under 10 
%!  Here in the hill country, if I'm doing something where I'm concerned 
about static, I wait for a very humid day.  Seems to take care of the 
problem.

The answer to the question about measuring the ground with a VOM is you 
can't do it.  A special instrument is used.  I think it's called a Megger. 
I've never used one.  The process I believe involves measuring the impedance 
between your ground and several other ground rods you drive a certain 
distance from your ground.  It is not a simple process.

A safety ground and an RF ground are two entirely different things.  A rod 
driven into the ground is never an acceptable RF ground.  When you set up a 
ground radial system, I believe it works through capacitive coupling between 
the radial system and the earth.  You can't even begin to measure that with 
a VOM.

Kerry