Would it be legal and possible to use 3/4" conduit to carry two 4 ga
conductors (hots) and one 6 ga conductor (neutral). That would be for
possibly upgrading a garage subpanel with existing 3/4" conduit. Most
bends would incorporate electrical boxes.
The reason, I suspect, is that you are planning for a 220v load that
you are sizing the 4ga hot legs for and the 6ga neutral is sized for
the expected 120v load. I would not try to get that in the 3/4" pipe.
Take the advice of a bigger pipe and run a 4ga (or match the largest
conductor you install, if you go smaller than the planned on 4ga.)
ground also, I this is going to feed a branch panel and therefore the
neutral ("grounded" conductor) and the ground ("bonding" conductor)
will not be tied toegther in the subpanel, only at the feeder (main)
panel in the house.
Nope, (except if you use imc conduit), but you would be much smarter to use
1" anyway - it would be an easier pull.
Look up the conduit fill tables in the NEC, you can even find those online.
Just remember tho, just because its legal doesn't necessarily mean its
smart. ie: sure you can legally put x conductors into a y sized conduit but
if the conduit is very long it gets to be absurdly difficult to get things
pulled in without damage. Using larger conduit makes for an easier job,
reduces the possibility of insulation damage, allows for future growth and
costs very little.
#4, when used as a Feeder, has an Ampacity of 100 Amps!
Do you *really* need that large a feed to a garage?
I'd go smaller and include an equip ground in the calc,
rather than use the raceway as the equip ground.
That computes to 41% a tad over what is legal but I doubt you could
actually pull it in anyway if there are a couple bends in the run.
If you really insist on trying this I suggest you dig down, cut off
the turn up 90s and put a LB on each end. Then it is a straighter pull
BUT IT IS STILL TOO MUCH WIRE IN THE PIPE.
Well then, you need to recalculate your load and see if you really need wire
that big. My instinct tells me I'd be willing to bet you're not doing
anything requiring more than the ampacity of an 8/3 or possibly (remote
chance)a 6/3 feeder, but of course i dont know your load or what you are
running out there. Again, my advice is to take a hard look at the loads you
plan to feed and see what you really need for a feeder.
If you are willing, post here what your plans are and we can give you some
feedback - maybe its a smaller job than you first thought - then again,
It is the type of insulation that matters in addition to the gauge of the
wire. Basically, if pulling more than one wire/cable through conduit, you
are only supposed to fill it to 40% of its cross-section diameter. Knowing
the sum of the cross-section diameters of the wire being pulled allows you
to see if you are within the 40% maximum.
In this case, using T90-Nylon (THHN) conductors will fill a 3/4" conduit
to 41.7%, so you really need to go with 1", though you could probably get
away with 3/4" but pulling will be a bit more work than it should. These
conductors only fill a 1" to 25.7%.
I have a Condiut Calculator available for free at:
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