Bob:
Your old house wiring may be BX, meaning it is wire in a spiral
armored casing, typically made of aluminum. While not ideal, you may
be able to gain an independent ground using this casing. It would
require (a) that the casing be continuous from receptacle to
receptacle, and (b) that it be well clamped with a BX connector to
each receptacle. In this case, you can add 3-prong plugs with ground
wires firmly connected (under a screw head, for example) to the
receptacle. Once you do this, you can get a "tester plug" from you
local jobber or hardware that can be used to determine whether all is
well. These tester plugs indicate with lights whether the polarity
is correct, the common is closed, and the ground exists.
best wishes,
dave belsley, w1euy
On Jun 11, 2006, at 8:24 AM, Don Wilhelm wrote:
While it is true that the white wire does connect to ground at the
service
entrance, that wire should not be considered a ground because it is a
current carrying conductor. Figure the voltage drop in one ohm of
wire
carrying 15 amps - that will produce 15 volts - and that voltage is
what
makes the white wire 'not a ground'. Additionally, if the white
conductor
should open at some point between your connection point and the
service
panel, it can become 'hot' with full line voltage on it. With the
sloppy
way I have seen some electrical connections done, the possibility
of an open
circuit is quite high.
Re-wiring your home may not be practical at this point (but it
would be a
wise step), but it would be practical to run a wire from critical
places
such as the ham shack or the workbench area to the service entrance
ground
as an added safety ground wire. If you use a separate ground for
the shack,
that ground should also connect back to the utility service entrance
(connect your added safety ground wire to the shack ground).
Remember that your safety is at stake anytime you plug an appliance
with a 3
prong plug into one of your ungrounded sockets. There is no
protection if
the appliance should develop an internal fault.
73,
Don W3FPR
-----Original Message-----
My house was built in 1978 before my area was annexed 5 years
ago. Bottom
line- No inspectors, no city code, I've got 3-wire plugs and
2-wire wiring
on every plug I've checked.
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-------------------------------------
david a. belsley
professor of economics
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