I have a long wall, about 100' along which I want to run 3 "staggered" or
"alternating" 120V branch circuits. What I would like to do is run 3/4"
conduit with a box every 4 feet or so. Then I'd like to have circuit "A"
appear at the first box and every third box thereafter. Then Circuit "B"
would first appear at the second box and every third box thereafter. And
finally Circuit "CB" would first appear at the third box and every third box
My question is whether code permits having all of the wires for three
separate branch circuits running through the same run of conduit and passing
through the boxes for the circuits they aren't connected in.
I assume you meant circuit "C" there at the end. I think this is OK if
you aren't over-filling the conduit. There are limits. You might even
be able to run a single neutral for all 3 circuits if you allow for
twice the amperage in that wire. I'd check with the local inspector
on that. In theory you would have 2 circuits on one phase and
1 circuit on the other so you could get 2X amperage in a shared neutral
in that situation.
I'm almost certain this is allowed within the bounds of conduit filling.
Your local inspector is your friend on getting the fine points.
No problem with the code in running separate 120v circuits in the same pipe.
You will have 6 current carrying conductors and you only need one ground.
You can use the <metal>conduit but a green wire is a whole lot better/safer.
Be sure you get big boxes. You will need 24.75 cubic inches if you only have
one receptacle, 26.75 for 2. (assuming #12)
Get 4x4x2 1/8 boxes with raised rings and you will be fine.
It is always better to use a big box. Easier to work in.
The other issue is derating but if you are using 90c wiring like THHN, it's
hard to find anything else, you will be fine with 6 conductors. (derated @ .8)
since #12 is good for 30a and #14 is good for 25a when you apply the derating
factor. You are still limited to a breaker size of 15a for 14 and 20a for 12 so
there is plenty of derating "wiggle" room.
Be sure not to put more than 4) 90 degree bends between pull points in your
conduit. Happy wiring!
Additionally, you will need to 'bond' your ground wire at each box and also
connect to each receptacle. Easiest way is to purchase or make separate
jumpers of bare solid #14 wire and attach it to the rear of the box in the
provided threaded hole using, if purchased, the green shouldered grounding
screw. ( #10/32x1/4) Then cut, strip and twist the ground wires to the
jumper leaving one wire extended long enough to secure to the receptacle/s,
subsequently secure with a green wire nut. They have a hole in the end to
allow the longer lead to protrude and still compress the twisted ones. Most
areas require any outlets not dedicated in garages to be ground fault
protected. GFIs can be daisy chained to protect additional standard
receptacles on the same circuit.
*YES* I've got 4 circuits through a common conduit, Double-gang boxes,
holding two duplex outlets each. With each outlet in any given box being
on separate circuits. Gives me 2 circuits at any location, and 4 circuits
'within reach' anywhere.
The required 6 wires for my config was a _hard_ pull through 1/2" conduit,
for the run with 4 90-degree bends in it (in less than 10 ft').
Care is required dealing with the neutral wires. Code requires that the
neutral be 'un-breakable' for the entire run. Have to pigtail on the
outlets at any intermediate point. can't wire to the 1st outlet and then
from that outlet to the next, (rationale: failure at the 1st outlet, or
botched repair, could result in 'unconnected' "neutral" at the downstream
outlet(s) -- a *definitely* unsafe condition. Thus, you've gotta be able
to connect/disconnect the upstream outlet w/o affecting the neutral to the
You could 'get away` with 1/2" conduit, but using 3/4" *will* make life a
lot easier, and allow room for 'something you haven't thought of' to be added
You might also look at a product called "Plugmold", from Wiremold Corp.
Surface-mount "conduit" with outlets built in at regular (options of like 3",
to 2', as I recall) intervals.
This is wandering off topic but yes you can run 3 phase WYE single phase loads
with one neutral. This is usually a douple sized neutral because harmonics can
make the currents add instead of cancelling.
It does point out aan important thing "on topic". Be sure you identify each
neutral in this pipe so you match up the load end with the feed end. With 3
there is an easy method, Use one white stranded and one white solid, the third
can be grey. (after the 2002 code change). Just be sure to write a note on the
back of your hand so you remember which is which.
I'm not an electrician, but I did exactly this. I have a neigbor who is a
residential wireman help me. When this question came up, he deferred answering
it and asked his electrician mentor, a master electrician. The answer was
I didn't do nearly as long a run as you, but in principle the same type of
Best to consult a master electrician in your area to make sure you're complying
with all NEC and local codes.
Run bigger conduit. The number of circuits doesn't matter, the number
of WIRES does.
I assume you are running 12ga wire. If I remember right, a 3/4 conduit
can run about 4 strands of 12ga. The conduit itself should be no more
than 20% full of wire, in order to allow heat to dissipate through the
And don't run Romex, if that's what you were planning. Romex cable is
not designed to be run in conduit---the cable sheathing is the conduit,
and putting more than one together in a small pipe will provide way too
much heat insulation, resulting in hot wires and noisy connections.
Passing through boxes isn't bad, as long as the box is rated for that
many wires. Each terminal box has (should have) a stamp or sticker
proclaiming how many "wires" it can handle, but the term "wire" is
strictly defined by the electrical code.
Is there a specific reason you are using conduit? If this is an
interior wall, why not simply run Romex through the studs? Conduit can
be a pain in the butt and an unnecessary expense.
I suggest you buy a homeowner-style wiring book, the Sunset "Complete
Wiring" book isn't too bad. It has a lot of really good basic
information like this. Further suggestion is to use individual wires in
1-1/4 inch conduit, or two runs of 3/4. I would use 3 hot wires, 1
oversize neutral, and 1 ground wire. All wiring connections MUST be
inside a terminal or junction box. (In other words, measure before you
Also, call your local permit office and ask to speak to an inspector.
They all know the codes and I'm sure they would be glad to help.
Please, please don't listen to this guy, he knows not whereof he speaketh.
Please, please do consult the NEC fill tables for the correct information
about fill percentages. (Hint, you can have many more than 4 strands of
12AWG THHN in a single 3/4" conduit). Note also that the ampacity of
the conductors must be derated based upon the number of current carrying
conductors in the conduit.
Noisy connections? WTF?
Again, consult the fill tables in the NEC. Boxes don't have stickers
with fill ratings.
If this is the book used for the information in this post, throw it
away, now. Better yet burn it so nobody else will use it.
Nuts. And a violation of code. The grounded conductor must be in the
same raceway as the current carrying conductor. Which, if one is using
either a so-called split-phase circuit, or an oversized grounded conductor for
multiple current carrying conductors,
implies that all conductors must be in the same raceway.
Well, one nugget of fact, after all.
Hey, there is one piece of good advice in this after all.
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