I have a dedicated 15-amp circuit in an unfinished basement that runs to an
outlet on the wall for the sump pump. The wire/cable that goes to the
outlet is white 14/2 NM-B w/ground. From the ceiling down to the outlet it
is fed inside of metal EMT conduit. I assume that the metal conduit is
1/2-inch (the outside diameter of the conduit is about 3/4-inch).
I would like to add a pull string ceiling light above the sump pump for
better lighting while working on the sump pump and/or the HVAC which is next
to the sump pump.
What I am thinking of doing is getting power for the light from the outlet
and running new 14/2 NM-B w/ground from the existing outlet back up through
the same EMT metal conduit to the new ceiling light.
My main question is, is it okay to have two 14/2 NM-B w/ground cables inside
a 1/2-inch EMT metal conduit?
On Fri, 12 Jul 2013 13:15:41 -0700 (PDT), firstname.lastname@example.org
334.15 Exposed Work.
In exposed work, except as provided in 300.11(A), cable shall be
installed as specified in 334.15(A) through (C).
(B) Protection from Physical Damage. Cable shall be protected from
physical damage where necessary by rigid metal conduit, intermediate
metal conduit, electrical metallic tubing, Schedule 80 PVC conduit, or
other approved means.
On Fri, 12 Jul 2013 16:32:46 -0700 (PDT), email@example.com
Not true at all for a single 14-2 NM.
A single conductor or cable can fill 53% of a raceway but when you get
to two, that drops to 31%
Ok to make the math easier this is metric
Using Southwire RX
14-2 9mm ...63.6 mm2
12-2 10mm..78.5 mm2
14-3 7mm....38.5 mm2
12-3 8mm....50.24 mm2
10-3 9mm....63.6 mm2
From Table 4
Trade size..one wire 53%...2 wires 31%....3 or more 40%
1/2"EMT....104 mm2 ...........61mm2............78mm2
3/4"EMT....102 mm2 ...........106mm2...........137mm2
1" EMT......295 mm2 ...........172mm2...........222 mm2
Two 14-2 RX would need a 1" EMT to be legal.
On 7/12/2013 11:31 PM, firstname.lastname@example.org wrote:
1" PVC might be easier to handle and install but I don't know about the
capacity. It's been a while since I installed any and I often used
calipers to compare the inside of different types of conduit when
planning a job. Scrap pieces of conduit and wire come in handy when you
want to do a practical measure of what you're installing especially when
it's signal or network cables that may not appear in any tables. Any of
the phone system or computer network installations I've done have 3/4"
EMT run to every phone or network outlet inside any wall but the wires
are not carrying any significant power. It makes it easier to install
the wires, besides, I'm lazy. ^_^
On Friday, July 12, 2013 2:15:55 PM UTC-7, Doug Miller wrote:
here NM is
NEC Note 9 in the Chapter 9 tables says
"A multi conductor cable of two or more conductors shall be treated as a s
ingle conductor for calculating percentage fill area. For cables that have
elliptical cross section, the cross section area calculation shall be base
d on using the major diameter of the ellipse as a circle diameter".
All that proves is that _that_particular_combination_ can't be run in _that_particular_size_ of
You made the blanket claim that "You can't have any NM cable inside a conduit" -- which is
complete and utter nonsense.
I don't know the answer to that question as I'm used to seeing THHN
instead... I'm assuming the reason for using NM is that the EMT just
terminates at a bushing above the ceiling, and is only used for
protection of the cable?
Is the recep in a 1900 (4" square) box or a handy box? If a 1900 box I
would just get another stick of EMT and do it that way. (don't forget
the bushing where the EMT terminates, to prevent chafing the NM.) If it
is a handy box you probably don't have enough room in the box to legally
add more conductors anyway, and should consider replacing it with a 1900
replace "roosters" with "cox" to reply.
If you run NM inside of metallic conduit, the metal should terminate in
you box using a proper fitting. At the other end of the conduit sleeve,
there should either be a choke or a bushing on the end of the conduit
and a staple into some framing near the end of the conduit. If you need
more cable entries in the box, use additional sleeves
Thanks Doug, gfretwell, RBM, Nate, et al.
I have another option that I think will work. The existing 14/2 NM cable
runs along the side of a ceiling joist close to where I want to put the new
light. Most likely, I can just unstaple that cable and create enough slack
to place a junction box in the circuit there and run the light from that
junction box. Or, if that doesn't create enough slack, I could just use two
But, before doing that, I thought that I would check to see if I could do my
original idea of having two NM cables in the one 1/2-inch metal conduit --
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