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.)
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."
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.
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.
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)
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.
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.