I am changing out some 2 prong (non grounded) plugs with three prong
(grounded) plugs on some equipment to make the equipment more safe.
Be careful about this. In equipment that uses a transformer power supply
it is probably okay to do this. Just make sure that the hot lead of the
power cord is the lead that goes to the fuse and the power switch. There
may be some transformerless equipment that does not have one of the two
wires connected to the chassis, and it may be okay to connect the
chassis on this gear to the ground lead. I AM NOT ADVOCATING ANY
MODIFICATIONS!
Most transformerless radios have one of the leads connected to the
chassis. Some have polarized plugs that are intended to insure that it
is plugged in such that the neutral lead is the one going to the
chassis. They are also built so that all of the parts you can touch,
knobs, switches, case are either insulating material (bakelite or other
plastic) if conductive they are insulated from the chassis and both the
hot and neutral power leads. They are built to be safe even if you do
get the plug in backwards. With this kind of radio there is usually no
place to connect the ground wire, because the ground and the neutral are
never supposed to be connected except at your building's load center
(circuit breaker panel or watt hour meter box). The three prong plug may
help prevent plugging the cord in backwards, but you cannot really use
the ground wire without violating the rule of keeping ground and neutral
separate.
If you have GFCI outlets or breakers in your building, connecting the
ground and neutral together should result in tripping the GFCI. A GFCI
protected outlet should trip whenever the hot and neutral currents are
not equal and opposite. With the ground connected to the neutral, the
return current will be divided between the ground wire and the neutral
wire. So the current in the neutral wire is no longer equal to the
current in the hot wire.
If you don't have GFCI protecting you, connecting the neutral to the
ground can create a hazardous situation. The voltage drop from the
current in the finite resistance of the ground wiring can raise the
potential of the ground prong. Another device, with a three prong plug
and grounded chassis, plugged into another outlet sharing the same
ground wire back to the load center, will now have a small AC voltage on
it's chassis, instead of the zero volts it would have if there were no
current flowing in the ground lead.
DE N6KB
|