🚀 go-pugleaf

In article <18425@mimsy.UUCP> spector@brillig.umd.edu.UUCP () writes:
> I've been told that the center screw and casing of the outlet boxes is
> generally grounded, [...] How do I (a vertual electronics know-nothing)
> check to see if this is working in my case?

	I've seen enough electrical systems to know that you shouldn't take
anything for granted.  I wouldn't even assume that a 3-pin outlet is really
grounded (from what I can tell, most electricians don't really understand
that there is a difference between ground and neutral).  Anyway, get a
volt-ohm meter.  Find a piece of copper plumbing (preferably a cold-water
supply line) and measure the voltage between the supposed ground point and
the copper pipe.  It should be essentially zero (you might well have
several volts between the neutral side of the outlet and the ground,
however).  Assuming you read zero volts between the ground point and the
copper pipe, switch the meter to the lowest resistance scale and measure
the resistance between the pipe and the ground.  It should be very low, a
few ohms at most.  If it is, you've got a good ground.  You might have to
clean up a bit of the pipe with sandpaper to make a good connection.

	If you either get any appreciable voltage (I would guess even a
tenth of volt on the ground is reason to be suspicious) or any appreciable
resistance (more than a few ohms) between the ground and the copper pipe,
your supposed ground is *probably* not really grounded.  It is possible
that the pipe is not really grounded -- there might be a piece of plastic
pipe somewhere between it and the earth, or some teflon joint tape might be
getting in the way, but by and large, if you've got solder-joint copper
plumbing, you should be able to count on any point in the cold water supply
being a good ground (but not the hot water supply; you don't usually have
metalic continuity through the hot water heater).  But, by-and-large, if
your "grounded" outlet fails the tests above, I'd bet it was the outlet
that was the problem, not the pipe.
-- 
Roy Smith, Public Health Research Institute
455 First Avenue, New York, NY 10016
{allegra,philabs,cmcl2,rutgers,hombre}!phri!roy -or- roy@alanine.phri.nyu.edu
"The connector is the network"