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We have a propane fireplace insert that can be wired up for a switch.

Right now, there are two 6" 18g single-strand leads that when nutted together complete the circuit allowing the fireplace to turn on when the main dial is st to 'on'. If you disconnect them, it goes back to pilot.

You can leave these connected and then turn the fireplace on by removing the front plate, but I wanted to hook up a remote switch to make it less of a chore. I went and got a low-voltage switch and ran 6' of 14g stranded wire to the switch to the two leads on the fireplace.

Alas, this doesn't work.

I'm guessing it's too much resistance to complete the circuit...either by length or gauge. Is there a rule of thumb here? If I go get single strand 18g would that work? Is there a way to calculate this short of trial-and-error?

UPDATE:

Well, I found an answer for my particular needs via trial an error. I'm not answer the question as there's probably a legitimate electrical formula for calculating this.

I took out the #14 stranded and replaced it with #18 stranded. Same length. But this works.

DA01
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  • The easy workaround would be to replace the switch with a relay, and extend the relay's control loop rather than the fireplace's own circuit. Then you'd know the exact specs for the relay and be able to make the appropriate calculations. Of course the manufacturer may also offer a remote control accessory, which would have the advantage of not voiding the warranty. – keshlam Jun 29 '14 at 04:19
  • Interesting idea...but wouldn't a relay have to be powered? – DA01 Jun 29 '14 at 05:15
  • Sure, but a cheap plug-in transformer can handle that -- including a leftover wall-wart from any random bit of electronics -- if you pick an appropriate relay. Nice thing about relays is that they let low-voltage circuits control higher voltage, while maintaining isolation between the two. – keshlam Jun 29 '14 at 13:00
  • Chapter 9 table 8 of the NEC, says that #14 stranded copper has a resistance of 3.14 ohms/kFT (10.3 ohms/km). #18 solid is 7.77 ohms/kFT (25.5 ohms/km). this answer, explains how to calculate the maximum length of a conductor. – Tester101 Jun 29 '14 at 13:27
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    Maybe the switch is the problem? Have you tried just connecting the wires together to complete the circuit - does the fireplace turn on? – Steven Jun 29 '14 at 14:59
  • @Tester101 uh oh. Now we're talking math. So, is that saying that the #18 solid is actually more resistant than the #14 stranded? – DA01 Jun 29 '14 at 17:11
  • @Steven nope. It's not the switch. It definitely appears to be the length of wire. I can sometimes get it to work with 6' of wire (looping one strand) But the two together (12') doesn't work at all. – DA01 Jun 29 '14 at 17:11
  • @keshlam if I had power to the FP, that would be a good solution. Alas, the insert is inside a masonry opening and getting power to it is going to be a bit of a chore. HOWEVER...maybe they make battery powered ones? – DA01 Jun 29 '14 at 17:12
  • Battery would work... but the power supply for the relay can be anywhere along the wire you're running to the remote switch, so if you can run the wire at all you can probably get power to it. – keshlam Jun 29 '14 at 18:41
  • Any idea what voltage you're dealing with? Could be just a few mV, in which case you'll lose it quickly by extending the circuit. – Tester101 Jun 29 '14 at 18:46
  • @Tester101 I forget what you call it, but it's not a circuit powered externally. I think it's one of those whatchamacallits that produces a bit of electricity via heat. I did find an answer, though...will post. – DA01 Jun 29 '14 at 19:32
  • Are you sure you have correctly identified #18 AWG stranded and #14 AWG stranded? #14 is the bigger wire. If they are both the same material (copper) the #14 has less resistance and so should work better. – wallyk Jun 29 '14 at 19:53
  • @wallyk Yep. The #14 didn't work. The #18 (thinner wire) did. Is that counter-intuitive? Again, it's not a powered circuit so maybe that's the issue? – DA01 Jun 29 '14 at 21:21
  • @DA01 That's why I asked, figured it might be powered by a thermopile. – Tester101 Jun 29 '14 at 22:00
  • @Tester101 yes! I believe that is exactly it. – DA01 Jun 29 '14 at 23:27

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