question about 120v stats

marsman716

Im an apprentice on a boiler crew and today i encountered a way of wiring 120v stats that i have not seen before. i asked my lead to explain it and he did but im still having trouble grasping it. basically there was a 3 wire coming down and that was controlling multiple stats through i think a common hot or common neutral. some how the stats share a hot or neutral. when the boiler was wired some of the stats only had 1 wire going to the r-w terminals on the zone relay instead of 2.

if anyone understands could you explain how this wiring configuration works.

HVACNUT

It was a cheap way of wiring a 2 story, 2 zone house.

14/3 Romex from the boiler to the first floor thermostat.

14/2 Romex from the first floor thermostat to the second floor thermostat.

White is Common and connects to the Line side of each thermostat, and R on Zone 1. (You might need to make a splice in the fist floor Gem box if there's not 2 Common posts on the thermostat.)

Red connects to the Load side of the first floor thermostat, and W on Zone 1 in the Zone Panel.

Black connects to the Load side of the second floor thermostat, and W on Zone 2 in the Zone Panel. (Black must be sliced through in the first floor Gem Box.)

The reason only one R is needed at the Zone Panel is because both zones share a what?... Beuller? Beuller? A "Common" feed.

**This ONLY works the way described if you're using a Low voltage circuit with Line voltage thermostats. And these Line Volt thermostats are obviously battery powered for switching because 24 volts isn't going to cut it.

If this is somehow still a Line Volt circuit with a "Zone relay", then there should be a couple of additional transformers somewhere.

Robert O'Brien

Very popular on Long Island from 1950-90

marsman716

https://forum.heatinghelp.com/discussion/comment/1809976#Comment_1809976

yea im here on long island. learning the quirks of the area has definitely been fun.

any other long island specialties i should know about?

marsman716

https://forum.heatinghelp.com/discussion/comment/1809974#Comment_1809974

is there a name for this wiring configuration? i would love to find a wiring diagram or schematic to study

HVACNUT

https://forum.heatinghelp.com/discussion/comment/1809996#Comment_1809996

I believe the wiring method is called "The Builder's Special". Maybe @EdTheHeaterMan can whip you up a diagram. He's got a system that puts NORAD to shame. I'm just on my phone.

EdTheHeaterMan

When @HVACNUT calls for a diagram, I will do my best.

With the limited information in this post, This is what I have come up with.

Click on the photo to enlarge and scroll around for the details.

I'm not sure what control box has the R and W terminals for a line voltage thermostat to connect to unless someone has built their own custom box like I have illustrated here. The lines in the green are how the different terminals may be interconnected. Based on the statement "some of the stats only had 1 wire going to the r-w terminals on the zone relay instead of 2." Here are two 120 VAC thermostats connected to one panel to operate different circulators. No relays are needed because the 120 VAC feeds the thermostats and from those 120 VAC thermostats feed the individual cirdulators 120 VAC. The Neutral from the Circulator motors get connected to the neutral from the power source.

The Hot 120 vac side gets connected to the W of the thermostat terminals and therefore feed 120 VAC to each thermostat. That white wire is not a neutral but part of a switch leg. A good practice is to wrap that white wire at both ends with black tape to indicate it is a HOT switch leg and not a neutral for future reference.

The Red and Black wires that return from the line voltage thermostats will then feed the respective circulator pumps. Since both W terminals are already connected internally in the control box, there is no need to run 2 hot wires from the W terminals in the same conduit to the first floor thermostat box.

My only question to @marsman716 is… Are you sure the thermostats are being fed 120 VAC? You know 14 gauge wire can carry 24 volts just as easily as 120 VAC or even @240 VAC. Exactly what control or relay box are these thermostats connected to.

If it is a switching relay or a zone valve relay that sends 24 VAC to the thermostats, you can do the same wiring design. Please advise if the control feeds 24 VAC to the thermostats and I can do the same diagram with a Taco ZVC 404, or SR 504. It's the same concept.

marsman716

@EdTheHeaterMan sorry i didn't make it clear in the post Ed, it was 24v being carried through old line stats with a taco relay

i actually tried to make a diagram based on @HVACNUT's description

Its rough but I believe its correct

EdTheHeaterMan

You got it right. Most of the zone controls have the marking R and W for thermostat. Some have T T. The ones with T T are the problem. You need to know which T is actually connected to R from the transformer. That is the one you need to connect to all the R terminals of the thermostats. In this diagram below I have illustrated the 24 VAC terminal on the control is connected to ALL the R terminals of the thermostat connections. That is the one that is common to all the thermostats. The faded red line from 24 VAC to R on each thermostat terminal board are all connected under the circuit board.

The White, Blue, Green, and Yellow are connected to the W on the thermostat. then the W on the respective thermostat terminals on the zone relays. I have illustrated the COM from the 24 VAC transformer in blue. They are all connected to the relay coil that operates pump motor, or zone valve on the ZVC controls. On zone 4, I have illustrated the path from the W thermostat terminal to the relay coil. You can use your imagination to connect all the other W terminals form each thermostat to the respective relay coils

And the reason there are 5 relays on a 4 zone relay is because of the priority switch. That has the ability to make zone 1, 2, & 3 stop when the DHW zone calls for heat. In this case, the priority switch is off, so zone 4 acts just like all the other zones.

You can see that a 5 wire is sent out of the relay with only one of the red wires connected. that is because all the other R terminals are connected under the circuit board. That red wire can feed all the R terminals on all the thermostats. It can be confusing, but it works. Once you understand it, then you can use this trick in the future to diagnose problems with thermostat wiring.

The important thing is to know which one of the thermostat terminals is R