thermostat wire in heating duct

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  #1  
Old 04-15-03, 09:33 AM
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thermostat wire in heating duct

can i run a 24volt wire through a section of heating duct.. obviously, i would buy wire with high temperature insulation.
if necessary, i can get datacom wire that has non-toxic insulation - used in suspended ceilings, etc.
 
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  #2  
Old 04-15-03, 09:53 AM
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Section 300-22(b):

Ducts or Plenums Usd for Environmental Air. Only wiring methods consisting of Type MI cable, Type MC cable employing a smooth or corrugated impervious metal sheath without an overall nonmetallic covering, EMT, flexible metallic tubing, IMC, or rigid metal conduit shall be installed in ducts or plenums specifically fabricated to transport environmental air. Flexible metal conduit and liquidtight flexible metal conduit shall be permitted, in lengths not to exceed 4 feet, to connect physically adjustable equipment and devices permitted to be in these ducts and plenum chambers. The connectors used with flexible metal conduit shall effectively close any openings in the connection. Equipment and devices shall be permitted in such ducts or plenum chambers only if necessary for their direct action upon, or sensing of, the contained air. Where equipment or devices are installed and illumination is necessary to facilitate maintenance and repair, enclosed gasketed-type fixtures shall be permitted.


You must used metal conduit inside. Why are you wanting to run wire thru your duct?
 
  #3  
Old 04-15-03, 10:10 AM
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because..

well, for starters, a two-conductor wire for a cooling thermostat was ALREADY in place when i bought the house. i want to combine that with an a/c thermostat which is currently a few feet away, so i wanted to run a length of 5-conductor wire and disable the old 2-lead. the thermostat is in a wall above a return grille, and the wire goes thru the duct, into the finished garage ceiling and then to the equipment.
 
  #4  
Old 04-15-03, 11:19 AM
texsparky
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Post Class 2 circuits

Use a Type CLP2 or Type CLP3 cable.They are rated for use in ducts,plenums and other space used for environmental air.
 
  #5  
Old 04-15-03, 11:21 AM
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If that's the only way to replace the wiring, I wouldn't worry about it. But, it would be nice if you could correct the violation by pulling your 5-wire cable outside the duct.
 
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Old 04-15-03, 11:26 AM
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i'm sure i can use clp2 or 3. thanks to all!!
 
  #7  
Old 04-15-03, 11:35 AM
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tex, correct me if I'm wrong, but I thought CLP cables were meant to be used in plenum areas such as above drop ceilings when the area is used for return air. They are not permitted to be used INSIDE ductwork.

That said, I don't see the harm in using them in bh's example.
 
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Old 04-15-03, 05:21 PM
texsparky
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mcjunk,

725.71 (A) Types CL2P and CL3P plenum cables shall be listed as being suitable for use in ducts,plenums, and other space used for environmental air and shall also be listed as having adequate fire-resistant and low smoke-producing characteristics.

Would the cables be plenum rated (hence the P ) without the listing ?
 
  #9  
Old 04-15-03, 05:34 PM
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mcjunk,
texsparky is correct as long as the termostat circuit is class 2 or 3. See 725.3(C).
Theoretically, the direction to use the CL2P or CL3P cable should only be made after you have confirmed that the power supply in the control cirucit is class 2 or 3. If not confirmed 2 or 3, then you must assume Class 1, and utilize a method from the wiring methods listed in your original post.
 
  #10  
Old 04-15-03, 06:14 PM
texsparky
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O.K.
Bruce, could you look at your x-fmer feeding the T-Stat and confirm whether it is Class 1,2,or 3 ? On my furnace,the x-fmer is Class 2 and also serves the A/C condensing unit.
 
  #11  
Old 04-16-03, 05:23 AM
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yep, class 2. thanks to all - amazing how much interest htis trivial subject generated!
 
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