I am trying to run a new electrical line but have a tight space where there
is a heating duct. That brings the cable close and potentially touching the
house heating duct. I saw a reference to cables in such a situation
requiring insulation or 1" air space.
What kind of insulaiton would you use. Household fibreglass? or is there
some special requirements.
This is Turtle.
I would try Wire hangers and a 1" air space. Anything less than 1" of air space
is less that what should be done. So you may try running the wire in flex
condiut till it passes the duct pipe and then pull the conduit away from the
duct with hangers as much as you can or get the 1" air space.
Where does this silly idea come from?
The 2005 code has specifically addressed this saying it is OK to put
cables in raceways. In fact stripping the jacket off voids the
As for the "fishing" question, look into"MC" cable. This is an
assembled cable in a spiral flex aluminum jacket.
On Mon, 07 Mar 2005 01:17:15 -0500, email@example.com wrote:
Don't know! Our state hasn't adopted 2005 NEC yet, the 2002 is still
the governing version. This will change in a few months.
But.... I've heard this so many times, to not put NM in conduit. When
right in ART 334 says you need to do it, when tranversing floors and
tells you to do it where physical protection is needed. Even a note
in Chapter 9 explains how to calculate size when using an
multiconnductor cable for conduit sizing.
To reiterate, I hear from any seasoned electricians, no cables in
conduit. The stick to their stories even after looking at the book,
but then, I guess they have to do what the boss says.
tom @ www.MedicalJobList.com
Code cite, please? Unless that's a change in the 2002 Code, I believe you're
Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?
The only time you should be stripping the jacket off romex is
when you've decided to use it for sculpture.
Can't you just use THHN cable? I'd be mildly surprised
if the heating duct operated in excess of 160F.
I think I mis-spoke here as to stripping the romex, not a good idea. I
meant that to go from romex to conduit you would have to go with individual
conductors. I have to be more careful in posting here, and to be clear in
the info given. I am an HVAC tech not electrician.
On 7 Mar 2005 18:44:42 GMT, firstname.lastname@example.org (Chris Lewis)
If the wiring method is conduit, single conductor is the cheaper way
to go, so common sense kicks in here, right?
Help me here, where is it that it's not permissiable to use sheath nm
in conduit where physical protection(you call "spot mechanical
protection")? Book is big, and I'm learning everyday.
Nipples need to worry about conduit fill, just that you goto 60%
column, instead of the others. I think the tiny-tiny piece for floor
transistions is ignored, but once again, I have to check the notes in
You are mentioning Canada a lot, so maybe we are in different books.
tom @ www.BookmarkAdmin.com
It boils down to something like this:
- you have to consider "conduit fill" (possible overheat
issues) and potentially conductor derating.
- when the wiring system _needs_ to be in conduit (ie: Chicago codes,
or hazardous location rules), you must use unsheathed cable. You
can't get away with stripping the sheath off and running individual
conductors. It's no longer a "permitted" use of the wire...
- when you're using it for "spot mechanical protection" of
a system that's otherwise permissible as NM, inspectors will give
you a certain amount of leeway. This is partially codified
(IIRC a 1-2' limit on "sleeves" without having to worry about
conduit fill), and partially "inspector permitted".
- whatever you do, they'll be concerned that it's done without
damaging the cable (eg: cable pulling grease if necessary)
For example, I've had inspectors approve 3-6' "drops" of NM
sheathed cable in PVC electrical conduit [*]. Mostly 14/2 (wg for
the Americans ;-) in 1/2" PVC, but also several of 14/3 and
even one of 10/3 also in 1/2" PVC.
[Note that in no case is there more than 3 current carrying
conductors in the PVC - the sheath wouldn't let you...]
In Canada, we also have a provision by which we can bury NMW
(aka UF, looks just like ordinary NM, only heavier) in PVC
black irrigation tubing (as long as it's the CSA-approved grade),
to reduce burial depth requirements by 6".
In both cases, while the length of conduit is longer than the 1-2',
the inspector knows that a free-air conduit on a wall is going
to be okay heat-wise, and buried system will generally not
have trouble with heating either.
[*] wired garage NM on ceiling, since walls already finished, the
shop outlets and switches are on PVC conduit "drops" on the
inside wall face to provide mechanical protection agains the
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
That is the reason we certify and license inspectors in Florida now.
Too many guys were making up rules as they went along
BTW what is the derating factor for 3 THHN conductors in a pipe? What
is it if these 3 conductors are in NM-b cable in the same pipe?
Hint: they are the same
ZERO derating ... in both cases
In fact, if you had FOUR 2 wire+g NM-b cables in a pipe (normal room
temperature) it could still be used at it's full rating.
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