18 gauge wire for line voltage t-stat????

D107

Had a serviceman come out to my mother's house to replace the non-functioning honeywell T8090A_T8191A chronotherm t-stat, which was 24vac as far as i know. Existing wire was 18 gauge (honeywell t-stat cable 18). They installed a Honeywell T451A3005, which requires 12 or 14 gauge. The 18 gauge, far as i know ran down to the basement where it joined the other t-stat low voltage line at a step-up transformer at a junction box. T-stats are hooked up to a .18amp taco relay which runs the circulators off a logamatic 2107 with outdoor reset.



I don't believe the tech ran new wire to the basement, so i can only guess he used the 18 gauge wire which i assume to be not code for a 120vac system. The company apparently only uses these commercial t-stats, which are much less sensitive than the low voltage. The new 3000 series is apparently a step up from older models in differential temp swing, and since this is a rear porch which does not need programmable, that's not the problem. It's the wiring I'm concerned about. Or perhaps I'm missing something. Any thoughts appreciated.

Mark Eatherton

I'm confused...

If it is only switching 24 volts, 18 ga. wire is fine.



If it is switching 120 volts, then it is probably NOT OK.



You can use a line rated switch on low voltage applications without having to raise the wire size, but am not sure exactly what it is that they are switching.



Wire size is based on voltage and amperage of the device being controlled, and developed length in the control circuit.



ME

D107

further info

"You can use a line rated switch on low voltage applications without having to raise the wire size"



thanks for your reply Mark. well I made the assumption that since the manual states it runs on 120vac it wouldn't be hooked up to a low voltage line. Prior t-stat was clearly low voltage. I may not have enough knowledge on these electronics to answer your question, but the primary control here is the Taco SR503-XP relay which draws .18amps and turns on the Taco 007 for the zone. Logamatic 2107 controls the Riello 40 F3. I think the length of the run to the relay is about 40ft.



Page 2 of the attached pdf states the electrical info.



Thanks again.

Mark Eatherton

You're OK David...

That stat is nothing but a bi-metal switch. It can be used with low voltage app's.



Your assumption about accuracy is correct. Your mom might have to fiddle with the settings to find HER comfort zone.



And it has ZERO anticipation capabilities, but it is what it is. A bi-metal Thermostat



ME

D107

Thanks

Well i guess that's what you get with a service contract. If I could have gotten out there soon enough there's plenty of more sensitive low voltage t-stats I could have put in. I can do that for next season. Thanks alot and have a great new year.