On Wed, 30 Nov 2005 18:18:48 -0500, " Uncle Peter"
wrote:


wrote in message
oups.com...
All,

I

If the radio has bypass caps on the line to chassis, and many do, you can
develop sixty or so volts AC from chassis to ground because the two
caps form a voltage divider. Measure the DC resistance between each
of the power lugs to the chassis, you should see infinite resistance.
Don't relay on the coax shell to provide a safety ground, you're only going
to end up getting knocked on your butt repeatedly when working on the
rig. The best bet is a three wire cord with safety ground.

Yup, as I said when in the earlier post where my FT101B tried to kill
me with a bare copper wire tied to a ground rod.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

Pete

Roger

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

OK that is one case where your need two failures to cause a hot chassis.
Now for Doofus to get electrocuted he will also have to have one
hand on this deaf radio and one hand on the radio that has a metal
chassis that is plugged into a socket with a good ground. The problem
you could also have a similar problem even if the neutral was wired
correctly (not tied to ground). If the ground wire broke in the cord or
inside the radio and then a capacitor or a transformer had an internal
short to the chassis or there was a resistor from hot to chassis ground
then the chassis would become hot. 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.

Yes it is not a good policy to tie the ground and neutral together. I
just felt that a good explanation of why not to do so was required
instead of just a blanket statement stating "The safety ground must
NEVER be connected to the neutral at the load !NEVER! "

But he on the safe side and ground those boatanchors together. (you can
buy a bigger boat that way).


Thanks
Ron WA0KDS









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.

Ron wrote:
OK that is one case where your need two failures to cause a hot chassis.
Now for Doofus to get electrocuted he will also have to have one hand
on this deaf radio and one hand on the radio that has a metal chassis
that is plugged into a socket with a good ground.

He won't know the radio is "deaf" until he trys to turn it on... and you
know Doofus, he broke the on/off knob years ago, and he always turns the
bare aluminum shaft while he is standing barefoot on the cement floor.

The problem you
could also have a similar problem even if the neutral was wired
correctly (not tied to ground). If the ground wire broke in the cord or
inside the radio and then a capacitor or a transformer had an internal
short to the chassis or there was a resistor from hot to chassis ground
then the chassis would become hot. The so called safety ground is not a
100% sure thing in the case of a failure.

Nothing is ever 100% perfectly safe. But you do try and improve the odds
as much as you can comfortably afford. Adding a safety wire system gives
you much more bang for the buck in terms of safety than the simple addition
of 33% more wire would appear to offer.

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.

Yes it is not a good policy to tie the ground and neutral together. I
just felt that a good explanation of why not to do so was required
instead of just a blanket statement stating "The safety ground must
NEVER be connected to the neutral at the load !NEVER! "

The problem here is I could write for the next week describing all of the
failure modes I know about that can and do happen with power distribution
grounds, and grounding. But I really don't have that kind of time. It
is far easier for me to tell you that doing such a thing is unsafe, and
that you should NEVER connect the safety ground to the neutral at the load.

If I tell you that E = I * R are you going to make me prove it? Or can I
just tell you from a position of assumed authority that this is a true
relationship? You can go and find a book that will tell you E = I*R, and
likewise, you can find a book, or do a google search, to find out why you
should NEVER connect the safety ground to the neutral at the load.

-Chuck

On 11/30/05 10:29 PM, in article , "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.

You declare that you will never understand the requirement, and obviously
have not searched for information about it, so why do you waste space with
such a post?

(snip)

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

Chuck Harris wrote:

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


Good point and thanks I think a few others understand the problem now
more than they did.

Don Bowey wrote:

On 11/30/05 10:29 PM, in article , "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.


You declare that you will never understand the requirement, and obviously
have not searched for information about it, so why do you waste space with
such a post?

(snip)


Just thought a little more info would be good for the group. I fully
understand the issue of grounds.

Have a good day and hope someone got a better feel for why AC grounds
are important.

Ron

Chuck Harris wrote:

Ron wrote:

OK that is one case where your need two failures to cause a hot
chassis. Now for Doofus to get electrocuted he will also have to
have one hand on this deaf radio and one hand on the radio that has a
metal chassis that is plugged into a socket with a good ground.


He won't know the radio is "deaf" until he trys to turn it on... and you
know Doofus, he broke the on/off knob years ago, and he always turns the
bare aluminum shaft while he is standing barefoot on the cement floor.

The problem you

could also have a similar problem even if the neutral was wired
correctly (not tied to ground). If the ground wire broke in the cord
or inside the radio and then a capacitor or a transformer had an
internal short to the chassis or there was a resistor from hot to
chassis ground then the chassis would become hot. The so called
safety ground is not a 100% sure thing in the case of a failure.


Nothing is ever 100% perfectly safe. But you do try and improve the odds
as much as you can comfortably afford. Adding a safety wire system gives
you much more bang for the buck in terms of safety than the simple addition
of 33% more wire would appear to offer.

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.

Yes it is not a good policy to tie the ground and neutral together. I
just felt that a good explanation of why not to do so was required
instead of just a blanket statement stating "The safety ground must
NEVER be connected to the neutral at the load !NEVER! "


The problem here is I could write for the next week describing all of the
failure modes I know about that can and do happen with power distribution
grounds, and grounding. But I really don't have that kind of time. It
is far easier for me to tell you that doing such a thing is unsafe, and
that you should NEVER connect the safety ground to the neutral at the load.

If I tell you that E = I * R are you going to make me prove it? Or can I
just tell you from a position of assumed authority that this is a true
relationship? You can go and find a book that will tell you E = I*R, and
likewise, you can find a book, or do a google search, to find out why you
should NEVER connect the safety ground to the neutral at the load.

-Chuck



Chuck I think you did a very good job and hope a few others good a
better understand of the problem. I just thought a little more info for
the group would no hurt. Being an Engineer I fully understand the
problem and Ohms law put most on this group I am sure are not and if a
new person who is us to solidstate circuit starts playing with
boatanchors it is totally different then being raised with them.

Again thanks and have a good day.
Ron
..

Okay, I fail to understand.

Formerly, the 2-wire cord was connected to pins 2 and 4 of the Yaesu
connector. These I assume correspond to the +hot and -hot of the 120V
input winding to the step up transformer, leaving the ground floating.
I looked at my 3-wire cord and determined that my hot wires were the
black and white ones for the 3-wire cord, and that neutral (chassis
ground) was green. So I connected wall ground through ground line of
the cord to chassis ground pin of the plug, leaving the hot connections
unchanged.

Is there something I should be doing different?

Thanks,

The Eternal Squire