I am sorry but the ground wire is also included in the calculations
because it too, can carry constant current in cases where protection
does not engage. Get your facts correct. The ground wire is just as
important of a conductor as any in a race way and is assumed to be able
to handle the full current load at 100% duty. If what you say is true,
which I know it isn't, we could put pissy small ground wire in the race
way, why waste copper. But that isn't the case because it isn't true.
You see, we know a lot about this subject because one of our sister
plants once got a citation for insufficient ground wire size and space
in a race way due to an accident investigation. The EMT had a short in
it but didn't trip the protection down stream. Some one got electrically
hurt, not killed but hurt. #6 AWG wires with #8 Ground wire in the pipe
with only enough clearance to account for the #6 wires and the ground
wire not being of said gauge by code. They got a fine even though it
wasn't the cause of the accident. The problem was physical damage caused
by a fork truck. Yes, the the fine also included improper guarding of
electrical areas and spacing.
The law suit put into place by the person that got injured never fully
follow through because about a mouth later, while said injured person
was suppose to be home recovering, was driving around and got side
railed and killed in an intersection accident. Of course, the person
having a alcohol problem I am sure didn't contribute to it.
Now if you want to talk about drain wires we can get on that subject too!
Btw, we manufacture high power wires and cables for a variety of
things. However, the power transmission systems in use in our facility
isn't any better then the average hack systems you see in most places.
The only good wiring that i've seen in house is what our own
electricians do for the production machines and offices. THey do follow
I do not know about the US, butt in the rest of the world, the reason
for "wasting" copper in the PE connector is not for carrying nominal
current for 100 % of the time, but rather to carry the fault current,
which typically is 4-10 times the nominal current. The idea is to
insure that the fault current is sufficiently large, in order to
_quickly_ burn the fuse or trip other safety device, while keeping the
ground potential rise at the faulty device at a safe level.
Even if the phase and neutral wires are thick enough to dissipate the
losses at nominal load, at least in Europe, you also have to consider
the total loop resistance from the fuse, through the most distant
outlet with some extension cords developing a short or ground fault.
The fault current must be sufficiently large to rapidly and reliably
blow the fuse.
Nope. For conduit fill, the reason for including the equipment
grounding conductor and/or bonding conductor is because they
take up space. The computation does not consider current. It is
strictly a physical size computation. For example, if you used
#10 awg on a 20 amp circuit, your computation has to be based on
the 10 awg conductor size, not on the 20 amp breaker.
For computing conductor ampacity derating, the ground or bonding
conductors and the neutral conductor that carries only unbalanced
current are not required to be counted.
See the NEC code: 310.15(B) (2) (a) (4) and
310.15(B) (2) (a) (5)
(4) Neutral Conductor.
(a) A neutral conductor that carries only the unbalanced current from
other conductors of the same circuit shall not be required to be counted
when applying the provisions of 310.15(B)(2)(a).
(5) Grounding or Bonding Conductor. A grounding or bonding conductor
shall not be counted when applying the provisions of 310.15(B)(2)(a).
Table 310.15(B)(2)(a) Adjustment Factors for More Than Three
Current-Carrying Conductors in a Raceway or Cable
He has his facts correct. See the NEC code article cited above.
What Bud said is true.
I suspect that this reveals that you think "derating" as Bud
used it means using smaller diameter conductors. That is NOT
what derating means.
You must use at least whatever the code requires for the
particular circuit - and the code doesn't allow "pissy small"
equipment grounding conductors or bonding conductors. I suspect
you are using the term "pissy small" to mean too small to safely
carry a fault current.
The equipment grounding conductor or bonding conductor is sized
to whatever the code requires for the particular circuit. If the
conductors will be run in conduit, then the size of the conduit
is computed based on the physical size and number of conductors
that will be in the conduit.
Guess you've never had to deal with those passing out citations to
violations.. They don't care how you, the violator interpret the rules.
I've seen the section that was used to make the citation valid, it was
clear and to the point!. You can read all the other side articles you
want and hope the one that counts does not get viewed, while your
defending yourself. Our lawyers can tell you all about how that one
I can say with out a doubt, you would never get hired at one of our
locations if you claimed to hold an E1 and practice like that.
I'll say no more on the subject, I've said too much already. It's
obvious you gamble, and if you do hold a E1, go a head and sign off on
those questionable jobs. Just hope no one tells you to start opening up
race ways for inspection.
You can go through the math and see that there is no need to include the
neutral in a total current derating of a conduit. The maximum power
transfer without exceeding a current X is when all three phases carry the
maximum current, X. In this case, the neutral carries zero current.
But what about unbalanced loads? The simplest case is one phase carrying
the maximum X and the others zero. In this case the total current is 2X,
less than the maximum 3X. If two phases carry the maximum and the other
zero, the neutral also carries X and the total is 3X, equal to that from
the max load. Any other combination also produces a total current of 3X
There is an exception. Very nonlinear loads like power supplies in
computers. They usually draw only during the voltage peak and the neutral
current often does not cancel completely. I've heard stories of how the
neutral has burned out when supplying a data center full of computers with
Don't let the actual code language get in the way of a good rant
"(5) Grounding or Bonding Conductor. A grounding or bonding conductor
shall not be counted when applying the provisions of 310.15(B)(2)(a)."
I already posted table 250.122 that debunks this myth.
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