Pretty Common Question

TheStressMachine

I read through articles and forum posts about the common wire until I started running into Lonnie Lynn, but I still can't correlate to my particular install. I'd like to get a common wire installed for a WiFi thermostat and already ran the new wire bundle, but need help on where to put the neutral.

I read here that it should connect on the same "thing" that provides the R, but in the examples it's typically a transformer. My R comes from a relay, and that's where I get too dumb to figure it out. I've attached a diagram showing my configuration, as well as pictures of the relay and transformer if that helps. Thanks in advance for your help, it's much appreciated.

hvacfreak2

Blue from the transformer is 24 vac hot , yellow is 24 vac neutral. You will need the yellow on C and the blue on R to power the stat. R closes to W on the thermostat to energize the burner.

hvacfreak2

Edit : I don't care for the junction box portion of the diagram. A nicer way.

TheStressMachine

Thanks for the response. Unfortunately I'm still confused (sorry I'm slow). Right now, brown from the relay goes to R on the stat, when the stat closes, W energizes blue. When you say "Blue on R" are you referring to when the stat is closed?

hvacfreak2

Blue goes to the R screw on the stat. Brown from the relay goes to the W screw on the stat. Yellow goes to the C screw terminal on the stat. Snap the stat back on the sub base. Apply power and operate per the instructions.

hvacfreak2

According to the diagram Blue and yellow come from the transformer . Blue is hot and yellow is neutral. Brown connects to the relay coil. Blue closes to Brown to energize the relay.

TheStressMachine

Right now on my stat the Brown is going to R screw and blue is going to W. I guess since it's just acting like a light switch the reversal doesn't matter, but I"m surprised it didn't tell me that it's getting voltage from W instead of R (it's a nest).

hvacfreak2

The current wiring scheme is causing confusion. On a two wire only thermostat it really doesn't matter which is connected to R or W. It's a single pole switch that closes , and as long as it does close everything works as intended.

The new stat requires power to operate. It just isn't a switch , it is now also a load so R and W now become specific . The brown wire in this case will not have power until it closes to blue
( power supply ).

And stay mellow through the process bro. Become
" TheMellowMachine" when working with low voltage wiring man.

TheStressMachine

Cool like the fonze, I only stress over things I'm good at :-)

Totally makes sense now. To be clear my new WiFi stat is running on two wire without a common, but it sometimes shuts down for a minute on long cycles because nests silly power siphon design isn't working well enough. I'm adding the common to make it more reliable, I was just surprised the nest was siphoning at all with the reversal (when the circuit is open). The wiring diagram makes a lot more sense too, going to swap the wiring in the junction jungle so the colors make sense and get the common connected to yellow. Thanks again for your help.

Steamhead

That looks like a Burnham boiler. The OEM transformer on these is typically mounted on an electrical box on the left side of the boiler, and all the wire connections are inside the box. If the transformer in the picture is mounted in that same location, it is a replacement for the original.

If the above is true, the blue wire is the "hot" and the yellow wire is the "common" or "neutral". The typical hookup in that case would be blue on the transformer to R on the stat, W on the stat to Brown on the relay, and C on the stat (if used) to Yellow on the transformer.

hvacfreak2

TheStressMachine said:

Cool like the fonze, I only stress over things I'm good at :-)



Totally makes sense now. To be clear my new WiFi stat is running on two wire without a common, but it sometimes shuts down for a minute on long cycles because nests silly power siphon design isn't working well enough. I'm adding the common to make it more reliable, I was just surprised the nest was siphoning at all with the reversal (when the circuit is open). The wiring diagram makes a lot more sense too, going to swap the wiring in the junction jungle so the colors make sense and get the common connected to yellow. Thanks again for your help.

" Dave's not here man " , lol. Good luck with the project.