I know it's generally a bad idea to put Romex (NM-B) cable inside of
conduit because of the increased heat build up. However, I'm curious how
big of a problem it would be for a short 3' section of conduit?

When we wired our house a couple of years ago, I installed a few runs of
1/2" pvc conduit from the panel down to our crawlspace in hopes of making
future upgrades easier. Now I want to run power out to a small shed using
8/3 wire. The 8/3 Romex just fits inside the 1/2" conduit and will work
great if that short section of conduit is acceptable.

The cable will run through our crawlspace to a junction box. From there
I'll use individual wires to run through 1" PVC conduit (already installed)
out to the shed.

Can I use the conduit, or do I need to resort to fishing cables through the
walls and floor?

What if I strip the outer cable insulation and feed the individual wires
through the conduit (with a cable clamp at the bottom of the conduit)?

Thanks,

Anthony

On 2005-06-10, HerHusband wrote:

I know it's generally a bad idea to put Romex (NM-B) cable inside of
conduit because of the increased heat build up. However, I'm curious how
big of a problem it would be for a short 3' section of conduit?

Well, here's what my 2002 NEC says: Chapter 9 Table 1 says the
acceptable wire fill for one conductor (or one cable) in conduit is
53%. However, Note (2) says "Table 1 applies only to complete conduit
or tubing systems and is not intended to apply to sections of conduit
or tubing used to protect exposed wiring from physical damage."

So in my ignorance, it sounds like it is OK.

What if I strip the outer cable insulation and feed the individual
wires through the conduit (with a cable clamp at the bottom of the
conduit)?

I've often wondered about that practice, it seems dubious to me.

Yours, Wayne

Wayne,

Well, here's what my 2002 NEC says: Chapter 9 Table 1 says the
acceptable wire fill for one conductor (or one cable) in conduit is
53%. However, Note (2) says "Table 1 applies only to complete conduit
or tubing systems and is not intended to apply to sections of conduit
or tubing used to protect exposed wiring from physical damage."

That's the kind of thing I was looking for. Thanks.

Since the conduit is open above and below, I would think any heat buildup
could escape easily.

Anthony

If you are going to run individual wires in the conduit out to the
shed, why not complete the conduit run from your stub out (or
down) to the pipe going to the shed and use the individual wires
for the entire run? Your are restricted to 360° of bends. If you
are any where close, install a junction box in your conduit run,
the j box would also allow you to change conduit sizes if this is
part of your problem.

(top posted for your convenience)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Keep the whole world singing . . . .
DanG (remove the sevens)




"HerHusband" wrote in message
...
I know it's generally a bad idea to put Romex (NM-B) cable inside
of
conduit because of the increased heat build up. However, I'm
curious how
big of a problem it would be for a short 3' section of conduit?

When we wired our house a couple of years ago, I installed a few
runs of
1/2" pvc conduit from the panel down to our crawlspace in hopes
of making
future upgrades easier. Now I want to run power out to a small
shed using
8/3 wire. The 8/3 Romex just fits inside the 1/2" conduit and
will work
great if that short section of conduit is acceptable.

The cable will run through our crawlspace to a junction box.
From there
I'll use individual wires to run through 1" PVC conduit (already
installed)
out to the shed.

Can I use the conduit, or do I need to resort to fishing cables
through the
walls and floor?

What if I strip the outer cable insulation and feed the
individual wires
through the conduit (with a cable clamp at the bottom of the
conduit)?

Thanks,

Anthony

Dan,

If you are going to run individual wires in the conduit out to the
shed, why not complete the conduit run from your stub out (or
down) to the pipe going to the shed and use the individual wires
for the entire run?

The junction box for the shed conduit is about 40' from the main electrical
panel. For cost and ease of installation, I'm opting to use romex between
the panel and junction box.

Anthony

HerHusband ) said...

When we wired our house a couple of years ago, I installed a few runs of
1/2" pvc conduit from the panel down to our crawlspace in hopes of making
future upgrades easier. Now I want to run power out to a small shed using
8/3 wire. The 8/3 Romex just fits inside the 1/2" conduit and will work
great if that short section of conduit is acceptable.

If it "just fits" you may be overstuffing the conduit. Maximum fill for
conduit is 53% of its cross sectional area for one conductor, but when
there is more than one conductor, it is only 40%. I suspect that pulling
a piece of Romex would count as more than one conductor (this limit is
from the CEC, but I suspect similar restrictions in the NEC as another
poster mentioned the 53% limit while quoting the NEC).

What if I strip the outer cable insulation and feed the individual wires
through the conduit (with a cable clamp at the bottom of the conduit)?

This is a viable solution, and one I've used in several instances.
All you have to do is put a fitting on the end of the conduit that
would be used to attach it to a junction box, and get a female-to-female
pipe coupling to couple the threaded end of the fitting to a threaded
cable clamp. Works very nicely.

By the way, I have free application called "Conduit Calculator" for
calculating conductor fill in conduit. It's available at http://daxack.ca

--
Calvin Henry-Cotnam
"Never ascribe to malice what can equally be explained by incompetence."
- Napoleon
-------------------------------------------------------------------------
NOTE: if replying by email, remove "remove." and ".invalid"

Calvin,

If it "just fits" you may be overstuffing the conduit.

Yep, my "Code Check Electrical" book says I can have a maximum of two 8
gauge conductors in 1/2" PVC conduit (for individual wires). But I'll have
four wires (8/3 w/ground) with the cable jacket. It fits into the conduit
easy enough, but I would clearly be exceeding the fill requirements for
conduit.

My main concern was whether it would be acceptable for such a straight
short run (3 feet). Doesn't seem like it would be all that different than
drilling a hole through a bunch of studs to snake the romex through.
Especially since it's a vertical section that's open at the top and bottom.

All you have to do is put a fitting on the end of the conduit that
would be used to attach it to a junction box, and get a
female-to-female pipe coupling to couple the threaded end of the
fitting to a threaded cable clamp. Works very nicely.

That was my plan if I have to resort to stripping the romex jacket back.
The conduit ends just above a foundation wall, so there isn't really room
to install a junction box there, and I can't really install bends in the
conduit with it being overfilled already.

If I have to, I could drill up from the crawlspace and snake the wire up to
the electrical panel. But, there's a LOT of cables in that stud bay under
the panel. The conduit would be so much nicer if I can use it.

Thanks for the input!

Anthony

According to HerHusband :
Calvin,

If it "just fits" you may be overstuffing the conduit.

Yep, my "Code Check Electrical" book says I can have a maximum of two 8
gauge conductors in 1/2" PVC conduit (for individual wires). But I'll have
four wires (8/3 w/ground) with the cable jacket. It fits into the conduit
easy enough, but I would clearly be exceeding the fill requirements for
conduit.

My main concern was whether it would be acceptable for such a straight
short run (3 feet). Doesn't seem like it would be all that different than
drilling a hole through a bunch of studs to snake the romex through.
Especially since it's a vertical section that's open at the top and bottom.

Under Canadian codes (like Calvin. Inspected/approved too), I've run 14/2,
14/3, 12/3 and 10/2 through 1/2" PVC for 5-7 foot "drops". Putting in
outlets, switches and a 30A cube heater outlet into my workshop, the
conduit is on the wall surface (not buried), and "sleeved" from the
ceiling to the boxes.

The inspector was fine with it.

That said, 8/3 sounds a trifle too far.

All you have to do is put a fitting on the end of the conduit that
would be used to attach it to a junction box, and get a
female-to-female pipe coupling to couple the threaded end of the
fitting to a threaded cable clamp. Works very nicely.

That was my plan if I have to resort to stripping the romex jacket back.
The conduit ends just above a foundation wall, so there isn't really room
to install a junction box there, and I can't really install bends in the
conduit with it being overfilled already.

Don't run the romex jacket back for running thru the conduit. If you're
going to go sheath-less, use proper unjacketed wire, with a J-box on
either end.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

Chris,

Under Canadian codes (like Calvin. Inspected/approved too), I've run
14/2, 14/3, 12/3 and 10/2 through 1/2" PVC for 5-7 foot "drops".
Putting in outlets, switches and a 30A cube heater outlet into my
workshop, the conduit is on the wall surface (not buried), and
"sleeved" from the ceiling to the boxes.
The inspector was fine with it.
That said, 8/3 sounds a trifle too far.

With usual hindsight, I wish I had installed larger conduit at the time.
But, it was a last minute idea I had before installing the sheetrock and
1/2" is just what I had on hand. I didn't figure I'd ever be adding any big
loads in the future. Funny what a difference a year makes...

I haven't checked the electrical supply stores, but if I opt to snake the
cable through the wall, my next concern would be the cable clamp at the
electrical box. A normal clamp fits in the hole and a nut gets tightened on
the backside. But, I'll only have access to the inside of the electrical
box. Do they make clamps that can be tightened from one side only? I've
never paid attention because I've never needed one before.

Anthony

According to HerHusband :
I haven't checked the electrical supply stores, but if I opt to snake the
cable through the wall, my next concern would be the cable clamp at the
electrical box. A normal clamp fits in the hole and a nut gets tightened on
the backside. But, I'll only have access to the inside of the electrical
box. Do they make clamps that can be tightened from one side only? I've
never paid attention because I've never needed one before.

There are plastic "snap-in" cable clamps that might help, but you'd
still need to get to the back of the boxes.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.