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Mixing high/low voltage in the same conduit #204859 01/16/12 04:28 PM
Joined: Jan 2012
Posts: 4
T
tbone Offline OP
New Member
I understand that normally, the NEC is not happy with mixing voltages in raceways, but I have an odd situation. I'm installing an electric radiant heated floor in my bathroom, and the thermostat I have chosen comes with a remote temperature probe.
I roughed in a deep j-box with sealtite run down through the sillplate, even with the floor so I can fish their special lead wires in when I'm ready to lay the floor. I then rocked the wall. Then, it occurred to me to look through the manuals, and they state that the remote floor temp sensor needs to be run separately, which makes sense from an NEC standpoint. This is when I found out that there was a remote temperature sensor! That being said, I'd really hate to deal with fishing this little cable up to the j-box, given how the wall is framed. Equally, I'd hate to fish a second conduit to this 1-gang j-box just for a 20-guage wire.

The odd part is that the sensor still needs to enter the j-box to get to the back of the thermostat, so it's not like the code is truly followed. You would think that the most-likely place for low and high voltage to accidentally come in contact would be in the j-box. So, my thought would be to use rubber refrigerator ice line (clear) and fish the sensor wires through that, then fish that through the high-voltage conduit. This way, I'm double-insulating the sensor wiring. Another possibility is to splice the sensor wiring to listed 20-guage thhn wires with the same insulation rating as their lead wires and fishing that through.

Products:
T-stat: http://www.aubetech.com/manuel/2/%282006_disc.%29%20TH115-A-F-AF.pdf
Radiant floor: http://www.thermosoft.com/radiant-floor-heating/installing-radiant-floor-heat/


Your thoughts?

Work Gear for Electricians and the Trades
Re: Mixing high/low voltage in the same conduit [Re: tbone] #204865 01/17/12 11:01 AM
Joined: Apr 2002
Posts: 7,233
HotLine1 Offline
Member
tbone:
Welcome to ECN Forums from one of the 'Jersey Guys'!!

Based on a quick read of the mfg instructions thru your link, I hate to tell ya to bite the bullet.

Mfg Instructions state 'seperate conduit' or staple to wall.

Using 'water tube' won't fly very well either.

Using THHN/THWN could work, IF you are not voiding the mfg warranty for the t'stat.


John
Re: Mixing high/low voltage in the same conduit [Re: HotLine1] #204866 01/17/12 12:41 PM
Joined: Jul 2004
Posts: 783
L
LarryC Offline
Member
Would sleeving the T-Stat wires in heatshrink be a viable option, if the shrink was listed for 300V?

Re: Mixing high/low voltage in the same conduit [Re: tbone] #204868 01/17/12 02:14 PM
Joined: Jul 2004
Posts: 9,569
G
gfretwell Offline
Member
The legal way I have seen to mix class 2 and line voltage in a conduit is if both are cables. You need to split them out before you cut into the cable jacket. (something like a "T" condulet at each end)


Greg Fretwell
Re: Mixing high/low voltage in the same conduit [Re: tbone] #204869 01/17/12 02:15 PM
Joined: May 2005
Posts: 984
G
ghost307 Offline
Member
The instructions clearly show the thermostat wire being routed outside of the outlet box, and therefore outside of the conduit run.

Sorry, it needs to run inside the wall, suitably fastened.
Even if it were permitted to run it inside the conduit, the device backplate is designed to keep it out of the box.

Re: Mixing high/low voltage in the same conduit [Re: ghost307] #204870 01/17/12 06:47 PM
Joined: Jan 2012
Posts: 4
T
tbone Offline OP
New Member
Now that I look at it closer, I DO see that unique type faceplate. Good eye! Bad for me, but good eye! I think I'll still run a rubber water line tube, but outside of the conduit, attaching it right below the j-box, so that I can fish in the sensor at a later point. The main problem is there is a fire block between the j-box and the floor, so it looks like I'll be doing some wall surgery. Ugh. Better now than later, I guess.

Re: Mixing high/low voltage in the same conduit [Re: tbone] #204875 01/17/12 11:48 PM
Joined: Apr 2002
Posts: 7,233
HotLine1 Offline
Member
You may want to get a piece of 'smurf' or another type of listed electrical flex. Your inspector may not like the rubber water line.


John
Re: Mixing high/low voltage in the same conduit [Re: tbone] #204938 01/23/12 11:38 AM
Joined: Jan 2012
Posts: 4
T
tbone Offline OP
New Member
Well, I blind-fished the stupid wires outside of the conduit, through the fireblock hole that that conduit went through. Since the fireblock hole was about a foot to the right of the jbox, I needed to hook it with a short fishtape from the gap under the jbox. It was the best blind double-fish job I've ever done. No wall surgery, and it only took me 15 minutes. I re-learned a valuable lesson to read the manuals of oddball electronics BEFORE you rock the walls. It would've saved me a lot of time.

Re: Mixing high/low voltage in the same conduit [Re: tbone] #204973 01/25/12 11:35 PM
Joined: Mar 2003
Posts: 849
Y
Yoopersup Offline
Member
Try Article 725.136


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