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Discussion Starter · #1 ·
I have a question in regards to running electrical cable across the dryer vent.

Here’s a picture of one house (front and back). Notice they put some protector in between the dryer vent and electrical cable.
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On the other house (below) there is nothing separating the dryer vent and electrical cable.
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Is there any code stating that electrical cable cannot touch a dryer vent?
 

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Naildriver
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No problem there. You have a plumbing wall which is extra thick and the cable and vent pipe can cohabitate that space just fine. If you feel better, you can place a piece of insulation between the two, but you don't want to pooch it out to where the sheetrock touches it. Just pull it away from the vent pipe so they don't touch.
 

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Discussion Starter · #3 ·
No problem there. You have a plumbing wall which is extra thick and the cable and vent pipe can cohabitate that space just fine. If you feel better, you can place a piece of insulation between the two, but you don't want to pooch it out to where the sheetrock touches it. Just pull it away from the vent pipe so they don't touch.
What happens if the wire and vent pipe touch?

The reason I ask is they stuffed the wall with insulation and the piece they pushed in most likely has the wire touching the vent now.

Wondering if that’s breaking code or can cause any issues?
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Naildriver
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Show us the side where the vent is. Your dryer won't get that hot and the heat dissipates pretty quickly. Like I said, grab a piece of insulation and put between the two as a feel good spacer.
 

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Discussion Starter · #6 ·
Show us the side where the vent is. Your dryer won't get that hot and the heat dissipates pretty quickly. Like I said, grab a piece of insulation and put between the two as a feel good spacer.
I don’t have the picture from the vent side, the wall is already dry walled and covered.

From left to right, it’s the dryer vent, electrical wire, insulation…looks like they pushed the insulation in from the right side, so I have to assume that wire is touching the vent.
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Never seen a dryer vent like that. Does the lint collect at the bottom and you clean it out there?
 

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The reason I ask is they stuffed the wall with insulation and the piece they pushed in most likely has the wire touching the vent now.
It's a code violation to have the cable be pinned against the wall. Cable must be placed so it cannot be damaged by a 1-1/2" nail driven into the finish wall. So while it would be nice to have it insulated from the dryer vent it would create issues of its own.

It's not an exhaust vent - OK I realize it's an exhaust vent, but the high volume of air moving through the dryer really dilutes the gas combustion heat, so it's not that hot. Yes, I know you have electric but you have to design for worst case.

And this is a new building? That's odd, they go to a lot of trouble to seal new buildings so they aren't drafty (because that dramatically increases HVAC costs). But having much less leakage means a dryer or vent fan can "pull a vacuum" on the building. And the problem there is if there are any combustion type heaters in the building, "pulling a vacuum" can cause their flues to run backwards and suck exhaust into the building. Not good. Newer gas things (except dryers and ranges) are supposed to have a direct vent, i.e. a dedicated air intake just for their combustion gases.
 

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Dryer vent temperature can be anywhere between 120° and 160° F.
UF wire temp. rating starts at 60°C.
In theory you could have an issue with the two in contact with each other.
More insulation around the pipe behind the wire would alleviate your concern.
 

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If it was hot enough to be an issue with wire it would burn your clothes you're drying up.

I don't know what you mean by "pinned against the wall." You can go shallower than 1 1/4" if you protect it with a nail plate. Most of his studs have them because he's close to the surface. There is at least one that looks like it is within 1 1/4 and is missing the plate though.
 

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The rule for the distance from a stud is 1 1/4" so if you are in the middle span of a stud space then the nm is not an issue of the 1 1/4" rule. The heat from the vent is insignificant as the wire is rated 90C which is over 190 F. It does not get that hot unless there is a fire in the wall...lol

This is what the code states. I am not so sure it is a great idea to be close to the sheetrock. The code states wood members specifically but someone can hang a picture anywhere. I guess if it is loose in the wall then it would move out of the way. With a dryer vent there it cannot move so sometimes we need to use our smarts.

If you are in an area where it is unlikely for anyone to drive a nail or use a screw then I say go for it.

300.4(A) Cables and Raceways Through Wood Members.
(1) Bored Holes. In both exposed and concealed locations,
where a cable- or raceway-type wiring method is installed
through bored holes in joists, rafters, or wood members, holes
shall be bored so that the edge of the hole is not less than
32 mm (11∕4 in.) from the nearest edge of the wood member.
Where this distance cannot be maintained, the cable or raceway
shall be protected from penetration by screws or nails by a
steel plate(s) or bushing(s), at least 1.6 mm (1∕16 in.) thick, and
of appropriate length and width installed to cover the area of
the wiring.
Exception No. 1: Steel plates shall not be required to protect rigid metal
conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical
metallic tubing.
Exception No. 2: A listed and marked steel plate less than 1.6 mm
(1∕16 in.) thick that provides equal or better protection against nail or
screw penetration shall be permitted.
300.4(D) Cables and Raceways Parallel to Framing Members and
Furring Strips. In both exposed and concealed locations,
where a cable- or raceway-type wiring method is installed parallel
to framing members, such as joists, rafters, or studs, or is
installed parallel to furring strips, the cable or raceway shall be
installed and supported so that the nearest outside surface of
the cable or raceway is not less than 32 mm (11∕4 in.) from the
nearest edge of the framing member or furring strips where
nails or screws are likely to penetrate. Where this distance
cannot be maintained, the cable or raceway shall be protected
from penetration by nails or screws by a steel plate, sleeve, or
equivalent at least 1.6 mm (1∕16 in.) thick.
Exception No. 1: Steel plates, sleeves, or the equivalent shall not be
required to protect rigid metal conduit, intermediate metal conduit,
rigid nonmetallic conduit, or electrical metallic tubing.
Exception No. 2: For concealed work in finished buildings, or finished
panels for prefabricated buildings where such supporting is impracticable,
it shall be permissible to fish the cables between access points.
Exception No. 3: A listed and marked steel plate less than 1.6 mm
(1∕16 in.) thick that provides equal or better protection against nail or
screw penetration shall be permitted.
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NM is only allowed to use 90C for thermal derate purposes (which is what we're doing here).

In all other respects NM must limit itself to the 60C thermal limit. NEC 334.80.



That weird exception is why NM is not mentioned on Table 310.15(B)(16).
 

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That's not what the rule says. The rule says you can't compute the ampacity above the 60C value even though you can start with the 90C values. 334.80 only deals with ampacity.
 
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