> From:    The Computer World <[log in to unmask]>
>
> Yes it is grounded well. And the monitors are at different places (different
> houses).
>
> In fact, once the monitor starts giving off voltage at its earth pin, all
                                                                        ^^^
> earth sockets in the house have the voltage. Once I disconnect the monitor
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> from the socket, the voltage is gone.
>
> Bharat

This indicates that the "earth" wire in your house is not properly grounded.
If it was properly grounded, it would take a current of many amperes to
produce a voltage of only one volt anywhere in the house.

(With the monitor unplugged), a voltmeter may show an induced voltage of a
few volts between "earth" and an independent ground (such as a steel rod
driven into the ground deeply enough to reach the water table, or a copper
water-pipe that connects to the city watermain).  This is because the "earth"
wires run parallel to the "live" wire and the meter may have an input
impedance of 20 MegOhms or more.  Any lower resistance should short this to
practically nothing.

This voltage check is to protect the meter when you switch to the Ohmmeter
settings.  The "earth" line, also called "protective ground" should be
solidly connected a water pipe or ground rod with a heavy green, or bare,
copper wire coming from your main power switch.  It should not be
confused with the "neutral" or "return" wire in two and three-wire circuits
which is also connected to this ground at ONE point only (at the
transformer or the main panel of a building).

The above applies to "grounded" systems as used in North America.  Europe
uses "ungrounded" loops and "double insulation" to protect people from
equipment with exposed metal parts becoming "live".  If you plug something,
such as an electric drill with a metal handle and a 3-prong plug (with a
"ground"/"earth" connection to the handle) into your power socket, you will
become "charged" with whatever voltage is present on your "earth" line when
you touch it.  If you also touch something grounded, such as a water tap,
radiator, or even a damp concrete floor, you could get a FATAL electric
shock.

I have seen this situation occur during a dry spell, when the water table
fell below the bottom of the grounding rod for a building.  It was bad
enough that you could light a neon bulb by holding it to the grounding
rod (at least 55 Volts!).  It also caused poor radio reception.  The fact
that we were practically in the shadow of a billion-watt radio transmission
tower didn't help either.  The chap who literally "put his finger on it"
happened to be the Chief Systems Operator for Hydro-Quebec at the time.
(He survived.<BG>)

Boyd Ramsay

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