I don't disagree with what you are saying, and I don't want
to belabor my point. Maybe I am being too esoteric or maybe
I read what you said wrong, but my intent was very narrow
case. You said, "Neutral (white) wire and safety ground
wire may be electrically same at breaker box end BUT are
electrically different at wall receptacle." I took that to
mean that at the receptacle the white wire was electrically
different compared to safety ground. I know that they are
electrically different at the receptacle compare to the
breaker box end. My point was that as long as nothing is
connected to or operating on that cable, there is no
difference between the two wires at any point along the
cable since they are both the same size and the same
length. You discussion is about operating appliances and
the function of each wire, and I don't have any argument
with that.

w_tom wrote:

The neutral and safety ground ARE electrically different. For
example, with a load on hot (black) and neutral (white) wires, a
voltage difference between neutral (white) and safety ground could be as
much as two volts at the receptacle. Why? An important concept.
Either end of wire, electrically, is not same. Wire is an electronic
component; a concept that makes understanding the code easier. In some
cases (ie. in this exampled, safety ground wire), electricity appears to
be same at both ends of safety ground wire. In the meantime, both ends
of neutral (white) wire are electrically different. Appreciate the
concept to understand why code is written. Wires are not considered
electrically same at both ends. Even though neutral (white) and safety
ground meet at breaker box, still, they are not electrically equivalent
in receptacle box.

That just for discussing electricity per NEC concerns. Then it gets
even more interesting. For interconnected electronics, if a safety
ground does not exist (circuit uses three wire receptacle but is only
two wires protected by GFCI), then electronic damage is possible (not
probably but possible). NEC does not address transistor safety. Such
potential damage to interconnected electronics is beyond the scope of
NEC. NEC is only concerned with human safety; not transistor safety.
Yes, the GFCI can justify three prong plugs (if marked accordingly with
a specific three word, NEC defined, expression). But safety ground also
provides functions.

Terms such as 'safety ground' are not NEC specific. 'Safety ground'
is used to make the concepts clearer for the reader. In grounding, the
outlet safety ground is different from the breaker box safety ground, is
different from the motherboard ground, is different from the computer
chassis ground, is different from earth ground. All are interconnected.
However each is a different ground with different functions. This in
part because no wire is a perfect conductor.

Same reason why safety ground wire connects breaker box to water pipe
(and in some jurisdictions, a ground is also made to gas pipe). It is
not an earth ground. Its function is to remove electricity from pipe -
for human safety reasons. Like wire, pipes are also not electrically
equivalent at both ends - which is why a safety ground connection must
not be made to water pipes elsewhere in the building. Pipes are no long
acceptable as a place to dump electricity - even if electricity is only
being dumped there during a very intermittent short circuit. Pipes must
not be part of any electrical circuit - which is a relatively new
concept in the code.

In the original post, noted was that neutral (white) wire and safety
ground wire are not same. Proof. Short neutral and safety ground
together at receptacle on an arc faulted (protected) circuit. Build a
little test plug and prove it yourself. See how long the circuit
remains functional. Any short between safety ground and neutral will
(eventually) trip an arc fault breaker because neutral and safety ground
wire must remain completely isolated; except in breaker box.

I don't have an arc fault protected circuit to test that and
I'm not sure how an arc fault protector work. However, I
realize that connecting the two at any point makes a
parallel path, so any load upstream will send half the
current down each wire to the breaker box. If an arc fault
protector measures current to the grounding wire, that's a
no brainer and not testing is needed. You are simply
putting current into a wire that is not supposed to have any
current except when something goes wrong. All this is
good, but it has nothing to do with what I said. I did not
say that you could use either wire, white or green (bare),
for a specific function. You cannot interchange the wires
or you screw up or loose the function of one or both wires.



Demonstrated by experiment - and so many reasons above - the neutral
(white) wire and safety ground wire are electrically different
everywhere except where they meet in breaker box.

George E. Cawthon wrote:

No. You miss read what I wrote (mistakes included), which
was that "there is no difference, it is how you hook up the
appliances." You're right of course, you cannot use them
interchangeably, but its no irrelevant that they are
connected at the panel. I was responding to a person that
said the two wires were the same electrically at the panel
but electrically different at the end of the wire. That
isn't necessarily true.