Ron wrote:
The so called safety ground is not a
100% sure thing in the case of a failure. Because safety grounds are as
prone to fail as anything a third external wire tying all metal cabinet
radios together is the only safety measure if one has a table full of
these old AC powered beasts.

I forgot to mention one additional tidbit: Safety ground wires are *not* as
prone to failure as are the current carrying hot and neutral leads.

I have repaired numerous power cords on portable appliances, drills, saws,
etc. There is one type of failure that I see over and over again, a broken
power lead inside of the cord, with no sign of failure on the outside.
The failure is usually at a point of stress, such as just after the strain
relief for the cord. When I take the cord apart (usually to shorten it,
and reconnect it inside the appliance) I have always found the break to be
one that looks as if someone snipped the wire off clean and square! There
is some blackening from the arcing that invariably occurs, but the break is
clean and square. This is not at all like the way a twisted rope fails.

I believe the reason for this, is a single strand breaks due to flexing, a
mfr. flaw, or stress. When this strand breaks, it increases the current density
of the wire at that point. The wire now gets hotter at the break, and this
makes it more prone to stress failures, and another strand breaks... then another,
and pretty soon the wire is seriously overloaded, and the rest of the strands
pop.

If I find a break in the safety ground wire, it is always a physical failure
caused by the wire getting wound up in the drill bit, or cut off by the saw, or
sheared off by a tool box in the bed of the truck.

-Chuck