Mains conduit fill question (N. America)

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.
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3/4 Inch EMT is acceptable per: http://www.electrician2.com/calculators/rf_calculator.html
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Per NEC all conductors must be included in the fill calculation.
?-)
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Actually need answer only to this Q:

Thanks,.
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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
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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.



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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 "
Copyright 1995, NFPA
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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.
?-)
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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--
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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.
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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. ;-)
--
John G.



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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)
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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.



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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
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Yes all conductors are counted for fill. You do not need to count the grounds for derating ampacity
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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 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.)
--
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Thanks people. 1" is required, larger desirable.
Cheers!
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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
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On Dec 21, 7:20pm, 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--
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wrote:

Often true, but always part of conduit fill calculations.
?-)
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