Taco Zone Valve - Electrical?

Steamhead (in transit)

to avoid problems with two transformers......

The problem is that TT on the boiler or multiple circ relay outputs 24V to what it expects to be a switch (thermostat) and takes that same 24V back in to operate the relay.

BUT...... the Taco 3-wire ZV puts out its OWN 24V to operate what it expects to be a relay.

The cure is to wire one side of the ZV transformer to terminal 2 on the ZV. Terminal 1 on the ZV goes to the thermostat and back to the other side of the ZV transformer. This is what energizes the ZV coil ("heat motor").

When the ZV end switch closes, terminal 3 on the ZV sends 24V to a relay (the "isolation relay") with a 24V coil and the other side of the relay coil goes back to the ZV transformer along with the wire from the thermostat. The dry contacts on the isolation relay are wired to TT on the boiler/multiple relay.

This way, the ZV operates a relay like it expects to, and the boiler/multiple relay TT terminals are connected to a switch, as they expect to be.

For up to 3 Taco ZV units, you can use a 40VA transformer. I like to use a "fan center" relay with these 3-wire ZVs, the kind the scorched-air guys use- most of these have 40VA transformers, and the built-in relay means I don't have to think about where to mount the isolation relay.

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Unknown

Circuit question...

I undestand how the valve works, when it sees power it heats up and the piston drives it open. Then it reaches a point where it turns on the aquastat through TT and then goes a little farther where it bounces off a NC switch to prevent overheating I guess. But it's just dawning on me, how does it isolate it's power xformer from the aquastat xformer? I just came across a boiler changeout situation with two water circuits. One with a pump and two zone valves and the other just a pump for DHW. Without thinking about it I got an SR502 board and connected TT from the valves to zone 1 on the 502 and THEN started thinking about the two transformers and whether they might be doubling voltage on me or doing something else equally as bad. But then I say TT on the aquastat is essentially the same as the 24 volt connections of the 502 so it should be ok? Seems wierd though...

Unknown

Thanks...

That's what I was thinking BUT if you look at a wiring diagram for them you will see that terminals 2 & 3 are shown wired directly to TT on the boiler control without any indication of an isolation relay. Guess I'll call Taco today. Out of curiosity if nothing else.

zeke

Two transformers can and are correctly shown in Taco's wiring diagram and there is no need for isolation since only one point is touching both transformers. As long as you have only one side of any transformer in contact with another there is no problem.

Joe Mattiello

TT terminals on the Taco control boards are the same as TT on the boiler. They are loaded with 24 volts, and running a 2, and 3 from a taco zonevalve directly to TT will not be a problem.

Unknown

Thanks all,,,

Seems wierd though

My best semi educated guess is that even though they share a common terminal each transformer seeks or follows it's own circuit without interfering with the other.

Electricity, it's some wacky stuff! LOL...

EdyLogicMstr.

Go to www.taco-hvac.com/uploads/FileLibrary/ZoneValveBroch.pdf and you will find on page 3 the wiring diagram from Taco that shows how two zone valve circuits "touch" each other @ terminal #2.