Mains conduit fill question (N. America)

[Bob E.]

Have three AWG 6, one AWG 8 (insulated ground) and two AWG 14 conductors (all
THHN or THWN) that need to run in conduit for < 20 feet.

I calculate the cross-section of the conductors and see that a 3/4" trade
size EMT conduit is too small and that a 1" size will carry these conductors
within code limitations.

Must the AWG 8 ground conductor be used in the fill calculation? Or only the
current-carrying conductors?

Just looking for confirmation.

Anyone?

Thanks.

 

[Bob E.]

Actually need answer only to this Q:

Must the AWG 8 ground conductor be used in the fill calculation? Or only the
current-carrying conductors?

Thanks,.

 

[Ecnerwal]

Have three AWG 6, one AWG 8 (insulated ground) and two AWG 14 conductors (all
THHN or THWN) that need to run in conduit for < 20 feet.

I calculate the cross-section of the conductors and see that a 3/4" trade
size EMT conduit is too small and that a 1" size will carry these conductors
within code limitations.

Must the AWG 8 ground conductor be used in the fill calculation? Or only the
current-carrying conductors?

It's presumably there in the NEC somewhere (I don't know one way or the
other off the top of my head), but the practical answer is, use 1-1/2"
or 2" or greater. Extra room in conduit is cheap, and terribly nice to
have later on. It also makes pulling a lot easier than fighting a
maximum fill load.

If you really want to hate yourself, you could run 1/2" for the #14s and
3/4 for the 3 #6 & #8 in parallel. The 3/4 will be fun to pull, but is
legit if you don't have the #14s in there.

I do have some 1" conduit - it carries 2 #10 wires out to my well (the
bare 2/0 ground wire is external so as to help the overall grounding
situation, as the well casing is the end of my ground network and there
are several ground rods driven into the bottom of the trench and
attached to the 2/0.) 1/2" is "more than adequate" for that much wire,
but I won't go smaller than 1" in a buried application, and then only
when I know the anticipated wiring for any anticipated use is well below
the fill for 1" conduit. I might add 3 more #10 or #12 to put an outlet
or two out by the well head - that's still 1/2" for fill.

Anything the least bit unknown just gets 2", so I don't have to chew
myself out later, and if a trench is involved, usually a completely
empty 2" run goes in as well as whatever is actually in the trench, just
in case. Conduit is cheap, trenches are expensive (not that you
mentioned a trench, but explaining my conduit philosophy as it applies
to trenches.)

 

[Bob E.]

Thanks people. 1" is required, larger desirable.

Cheers!

 

[Jamie]

Have three AWG 6, one AWG 8 (insulated ground) and two AWG 14 conductors (all
THHN or THWN) that need to run in conduit for < 20 feet.

I calculate the cross-section of the conductors and see that a 3/4" trade
size EMT conduit is too small and that a 1" size will carry these conductors
within code limitations.

Must the AWG 8 ground conductor be used in the fill calculation? Or only the
current-carrying conductors?

Just looking for confirmation.

Anyone?

Thanks.

yes, the ground is also included in the math, why? because the ground
also carries current when things go wrong and you don't want it to over
heat in the pipe before the protection kicks in.

Besides, it don't hurt to have some extra room.. Just go to the
next size, you won't be sorry. You'll be able to pull the wire much
easier now and later if needed.

Jamie

 

[ehsjr]

Actually need answer only to this Q:




Thanks,.

You must include the AWG 8 (or whatever size wire you use)
equipment grounding conductor or bonding conductor in the
conduit fill calculation.
From the NEC: "Equipment grounding or bonding conductors, where
installed, shall be included when calculating conduit or tubing
fill. The actual dimensions of the equipment grounding or bonding
conductor (insulated or bare) shall be used in the calculation."

Ed

 

[Bob E.]

What is the rule about Grounding conductor in the US?

Should it be as big as the active conductor to carry the fault
current??
John G.

I believe the National Electrical Code (NEC)

<http://en.wikipedia.org/wiki/National_Electrical_Code>

allows for reduction in grounding conductor of one AWG wire size. For
example, AWG 8 grounding conductor can be used with AWG 6 current-carrying
conductors.

That's a *general* rule, for which there are always many exceptions in the
minutia of the NEC.

 

[Bob E.]

The more I read about the NEC the more I do not understand. ;-)

John G.

Are you sure you're not a Yank? ;-)

Wire size is enumerated by 2's (AWG 14, 12, 10, 8, 6, etc.) yet we call steps
from one size to another "one wire size". What ever happened to AWG 13? Or 7?
Inquiring minds want to know!

Bob (the OP)

 

[Bill Gill]

Bob E. explained on 22/12/2011 :

Thanks Bob,
I live in Aus and am not an Electrician.
I just wondered if it had any effect on the OPs question.

The more I read about the NEC the more I do not understand. ;-)

The NEC is not to be understood. It is to be followed, if you
can figure out what it says.

Bill

 

[Jamie]

The ground is included in sizing the conduit (the OP's question)
because it takes up space.

The ground (and, in general, neutrals that carry only unbalanced
current) are not counted as current carrying conductors for
determining derating of allowed wire "ampacity".

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
protocol.


Jamie

 

[[email protected]]

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.

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.

 

[ehsjr]

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.

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)

Quote:
(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).

Quote:
(5) Grounding or Bonding Conductor. A grounding or bonding conductor
shall not be counted when applying the provisions of 310.15(B)(2)(a).

Quote:
Table 310.15(B)(2)(a) Adjustment Factors for More Than Three
Current-Carrying Conductors in a Raceway or Cable

Get your facts correct.

He has his facts correct. See the NEC code article cited above.

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,

What Bud said is true.

which I know it isn't,

You're wrong.

we could put pissy small ground wire in the race

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.

Ed

<snip>

 

[josephkk]

Have three AWG 6, one AWG 8 (insulated ground) and two AWG 14 conductors(all
THHN or THWN) that need to run in conduit for < 20 feet.

I calculate the cross-section of the conductors and see that a 3/4" trade
size EMT conduit is too small and that a 1" size will carry these conductors
within code limitations.

Must the AWG 8 ground conductor be used in the fill calculation? Or onlythe
current-carrying conductors?

Just looking for confirmation.

Anyone?

Thanks.

Per NEC all conductors must be included in the fill calculation.

?-)

 

[josephkk]

ehsjr used his keyboard to write :

What is the rule about Grounding conductor in the US?
Should it be as big as the active conductor to carry the fault
current??

Not required to be that large by the NEC but may be required to be so by
local code. Personnally i consider it to be proper design.

?-)

 

[josephkk]

The ground is included in sizing the conduit (the OP's question)
because it takes up space.

The ground (and, in general, neutrals that carry only unbalanced
current) are not counted as current carrying conductors for
determining derating of allowed wire "ampacity".

Often true, but always part of conduit fill calculations.

?-)

 

[josephkk]

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)

Quote:
(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).

Quote:
(5) Grounding or Bonding Conductor. A grounding or bonding conductor
shall not be counted when applying the provisions of 310.15(B)(2)(a).

Quote:
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.


You're wrong.


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.

Ed

<snip>

Thank you Ed. Jamie should pay attention to Article 250.

?-)

 

[Jamie]

Thank you Ed. Jamie should pay attention to Article 250.

?-)

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
plays out.

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.


Jamie