# Mains conduit fill question (N. America)

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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.

## Re: Mains conduit fill question (N. America)

3/4 Inch EMT is acceptable per:
http://www.electrician2.com/calculators/rf_calculator.html

## Re: Mains conduit fill question (N. America)

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

?-)

## Re: Mains conduit fill question (N. America)

Actually need answer only to this Q:

## Re: Mains conduit fill question (N. America)

Bob E. wrote:

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

## Re: Mains conduit fill question (N. America)

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??

--
John G.

## Re: Mains conduit fill question (N. America)

wrote:

You use table 250.122 to size grounding conductors based on the
breaker/fuse that served that circuit

Amps               copper            aluminum
15                  14                    12
20                  12                    10
30                  10                     8

40                  10                     8
60                  10                     8
100                   8                     6

200                   6                     4
300                   4                     2
400                   3                     1

500                   2                   1/0
600                   1                   2/0
800                 1/0                   3/0

1000                 2/0                   4/0
1200                 3/0                   250 kcmil
1600                 4/0                   350  "

2000                 250 kcmil             400  "
2500                 350  "                600  "
3000                 400  "                600  "

4000                 500  "                800  "
5000                 700  "               1200  "
6000                 800  "               1200  "

## Re: Mains conduit fill question (N. America)

wrote:

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.

?-)

## Re: Mains conduit fill question (N. America)

In the NEC ground wires are covered by 250.122
[there is a post from gfretwell at alt.engineering.electrical, not
crosposted to sci.electronics.design, on this]

Ground wires need to be big enough to produce a fault current that
will rapidly open the overcurrent protection. The NEC allows, as
circuit amp rating increases,  a much smaller ground wire than the
circuit amp rating would indicate. For instance for a 400A circuit a
#3 copper ground wire can be used - rated around 100A.

If the small ground wire produced dead bodies the code would have been
changed.

--
bud--

## Re: Mains conduit fill question (N. America)

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.

## Re: Mains conduit fill question (N. America)

Bob E. explained on 22/12/2011 :

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. ;-)

--
John G.

## Re: Mains conduit fill question (N. America)

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)

## Re: Mains conduit fill question (N. America)

Bob E. formulated the question :

Spent 6 months helping loose the VietNam war in64/65.
Lived with my family in various places, San Jose and Poughkeepsie,
(clue to employer) for most of 1968.
Various business trips over next 20 years,worked in Hong Kong Office
for 2 years with many Yanks.
Yeh I have been confused with Yanks occasionally.

--
John G.

## Re: Mains conduit fill question (N. America)

On 12/21/2011 11:35 PM, John G wrote:

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

Bill

## Re: Mains conduit fill question (N. America)

Yes all conductors are counted for fill. You do not need to count the
grounds for derating ampacity

## Re: Mains conduit fill question (N. America)

In article

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

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.)

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.

## Re: Mains conduit fill question (N. America)

Thanks people. 1" is required, larger desirable.

Cheers!

## Re: Mains conduit fill question (N. America)

Bob E. wrote:

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

## Re: Mains conduit fill question (N. America)

On Dec 21, 7:20=A0pm, 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".

--
bud--

## Re: Mains conduit fill question (N. America)

wrote:

Often true, but always part of conduit fill calculations.

?-)