Ron wrote:
I believe the important thing here is that a three wire plug be used and
that it gets wired correctly. I will never see why the neutral which is
grounded and green wire which is ground cannot be tied together. The
key here is that the plug can not get reversed like it could with the
two wire plug so getting hot AC on the chassis can never happen. If the
socket is miswired than as soon as you plug in your radio with the green
and neutral tied together your main fuse will blow. I sure would like to
know what certain wiring failure modes could energize the chassis ?
Ground is Ground period. If the original two wire plug would have been
polarized in the very beginning I expect that three wire plug would have
never happened.



Hi Ron,

You are thinking like a newbie engineer... you haven't yet discovered
multiple failures, and mistakes. If nothing fails, you are right, there
is no harm in tieing the safety ground and neutral together.

But let's first discuss the purpose of the safety ground: It
is there to make it very unlikely that the cases of appliances could ever
become elevated above earth ground. This is to protect a barefooted doofus
from getting electrocuted when he is standing on the cement floor in the
basement, and trys to operate his FT-101E. The *secondary* purpose of the
safety ground is to provide a return that will blow the circuit breaker if
the hot lead accidentally becomes shorted to the case of the FT-101E.

The way the safety ground provides these protections is by being
connected to the centertap of the pole pig (neutral), and to a grounding
rod that sticks into the earth at the house. This connection is done
at the service panel where power service enters the house. The grounding
rod is there to make sure that the safety ground, and thus the cases of
the appliances, stays at the same potential as the cement floor in your
basement.

Back in the old 2 wire days, when the neutral side of the plug wire was
connected to the chassis, and you were expected to turn the plug around
until it didn't tingle, if the cord's neutral wire broke, current would
pass through the appliance's circuitry to the chassis connection, and
as a result the chassis would become hot relative to the earth ground
(Doofus's feet on the concrete slab). Doofus would be pushing up daisies.

Let's move forward to the days of the 3 wire plug, and the safety ground...

Saint Chuck has wired Doofus's FT101E so that the hot lead goes to Hot+,
and the neutral lead goes to Hot-, and the safety ground lead goes to the
chassis:

Doofus, likes to unplug his FT101E whenever he isn't using it, and he likes to
windup the cord to look just like it did when the radio was new-in-the-box.
After doing this for a while, the hot, or neutral lead breaks. Doofus plugs
in his radio, and turns it on, and it doesn't work! So he asks Saint Chuck
to fix his radio, and life marches on. If, on the other hand, it wasn't the
hot, or neutral lead that was broken, but rather it was the safety ground lead,
Doofus wouldn't know it was broken, and would continue to operate, a little
less safe, but still safe, because the radio was wired correctly... and if
somewhere down the path, we added an additional wire to the broken safety
ground, the radio would stop working, but would still be safe.

Now, lets suppose that instead of Saint Chuck wiring Doofus's FT101E, it was
wired by some squire. This squire wired the hot lead to Hot+, and then wired
the neutral lead, safety ground lead, and chassis to Hot-.

Back to Doofus:

Doofus, likes to unplug his FT101E whenever he isn't using it, and he likes to
windup the cord to look just like it did when the radio was new-in-the-box.
After doing this for a while, the neutral lead breaks. Doofus plugs
in his radio, and trys it out, and it works just fine! Doofus continues
operating this way, and eventually, another wire in the cord breaks. If
that wire happens to be the hot lead, the radio will quit, and barefoot
Doofus will take the radio back to the squire for a rewire job. If that wire
happens to be the safety ground lead, the chassis of the FT101E will now be
at full power line potential (current passing from hot lead through the radio's
circuits, to the chassis/hot- connection), and barefoot Doofus will be
pushing up daisies.

The safety ground must NEVER be connected to the neutral at the load!
NEVER!

Be safe, allow for multiple failures, and fix the cord so that the hot lead
goes to hot+, the neutral goes to hot-, and the safety ground lead goes to
the chassis.

-Chuck Harris