I need to add a sub-panel about 40 feet away from my main panel. The
previous owner left an empty 3/4 inch run of conduit in case anyone
wanted to add a sub-panel to the other side of the house (for an
addition) (conduit runs interior sub-panel will be interior). Now is
the time for that addition. I would like to run #6 wire to the sub
panel because one of the new branch circuits will have a 30 amp steam
unit for the bath. Ideally I'd like to run #4 wire even if I can.
The 40 foot run only has one 90 degree bend right at the main panel
and I could put a large pull box at the other end prior to bending
into the sub panel with any size pipe I want.
Can I get three #4's in 3/4 inch thinwall or must I use #6? My
intention was to undersize the feed breaker in the main panel to
accomodate whatever wire I can get into this pipe.
Must use #6 (THHN); 3/4 won't accept #4.
4 #6 allowed.
I would pull 3 #6 plus 1 #8 (or #10) Grn Equip Ground.
60 Amp breaker. (Technically, could be a 70)
With the steam unit (Line-to-Line), it might be possible
to use a reduced Neutral size for the feeder, but that may be
making things too complicated...
The steam unit outlet will come off one of the sub panel branch
breakers (30A/220V GFCI) thats no problem as that outlet is not yet
roughed in. The remainder of the branch breakers in the new sub panel
will be for misc lights and outlets in the new addition. 60 amps
total to the sub panel via 3 #6 should be plenty plus a #8 or 10 bare
safety ground wire. (considering my entire first home had 60 amps
Then you would suggest re-grounding the new sub panel with the bare
wire (in addition to the natural conduit-created ground)? Just to
make sure it has a good tight ground? I'm assuming one should not re-
bind the neutral again in any sub panel, is this true? FYI I'm having
an apprentice electrician do the work (my nephew) I just like to know
what's going on capacity-wise.
Meant to say:
I'm assuming one should not re-bind the neutral to ground again in any
sub panel, is this true? Should the neutral-to-ground binding only
occur once in a house (at the meter or main panel)? No matter how
many sub-panels you have.
Right you are. The new sub-panel may come with a Bonding
screw intended to bond the Neutral bar to the enclosure/box.
Throw the screw away. :-)
If the panel doesn't come with one, you will need an
accessory Grounding bar so that the bare gound wires (Romex)
can be terminated on it, rather than on the Neutral bar.
Thats what I thought, re-binding a neutral in a sub panel would make
the ground wire from the main panel into a normal-condition load
carrier. And it is my understanding that safety ground must never
carry a load in normal-condition, rather only when the connected
device has a fault.
Four #6's in a 3/4" conduit is gonna be a tough pull. 8's are *much*
easier to pull (even easier than #10), so use #8 for the ground and
maybe #8 for the neutral if you can. That will leave more room for your
You can only run two #4's in a 3/4" conduit.
Table 3B "Maximum Number of Conductors in Trade Sizes of Conduit or
Tubing" in the back of NFPA 70 says 4 conductors (THHN or THWN) are
allowed in 3/4". (I thought only 3 were allowed until I looked it up)
Maybe you looked up TW?
Last night I easily "pushed" 3 #6 and one bare #8 through the 40 foot
pipe after taping the tip into a bundled point, luckily there was only
one 90 degree bend down into the main panel. I did use some pulling
lube so it pushed nicely all the way to the other side of the house,
and all the wire was stranded to make the turn easier. All I have to
do now is pipe a turn down into the new panel once I mount that, then
have my nephew who is a union apprentice finish up.
Technically a solid #8 is not legal in a conduit unless it is a
grounding electrode conductor but if you did manage to get it in there
I don't really see a danger. It is just a pulling issue. In a fairly
straight run it isn't really a problem. In fact I have one set up in
my house exactly the same as yours (3 #6s one #8.)
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