Basic question about 240v wiring

Thread Starter

mikemc

Joined Nov 2, 2021
11
May I please ask a question about wiring domestic heating controls.

I have 2 separate controllers controlling 2 separate heating systems.

Each controller can send a 240v "call for heat" signal to the boiler via a single core cable.

What device do I need to allow the separate input wires to be connected to the boiler whilst preventing the voltage from one wire passing back up the other wire?

Many thanks for any advice
 

olphart

Joined Sep 22, 2012
107
Much more detail required. For one: I doubt the controller signal uses 240, almost certainly a much lower control voltage.
 

Thread Starter

mikemc

Joined Nov 2, 2021
11
Fair comment. I didn't want my question to seem to laborious.

There are 2 separate circuits comprising a 24v controller, a pump module with a 240v supply, and a circulating pump. Both circuits control heat from the main heating boiler. When heat is required from either circuit the relevant controller will send a 24v signal to the pump module which then switches a 240v supply to its own pump. At the same time the pump module sends the 240v signal to the boiler's "call for heat" terminal. Both the pump feed and the boiler feed coming out of the pump modules share the same terminal in the module.

I need to make sure that the feeds from each pump module only travel in one direction - from module to boiler. Otherwise, when one "module to boiler" feed becomes live it would travel back up the "module to boiler" feed on the other circuit. This wouldn't matter if we were only dealing with the module and the boiler. But that feed would also energize the other pump unnecessarily via the shared terminal in the module.

So live 240v 2 wires going into 1 but only able to travel in one direction. Do I need some kind of relay or diode?
many thanks
 

ronsimpson

Joined Oct 7, 2019
2,022
Do I need some kind of relay or diode?
A diode works if the signal is DC but I think the 24V is AC.

In my system there are 5 thermostats, which open and close 5 valves, all using one common 24Vac power.
Each valve has a module, which is simply a switch that shows if the valve is open or close. (valve open = switch closed) All the valve switches are wired in parallel so that when any valve is open the switches will pass 24Vac to a relay that sends (220 or 110) power to the boiler and pump.

Please send a picture of the " controller ".
 

Thread Starter

mikemc

Joined Nov 2, 2021
11
Thanks

The 24v signal isn't really the issue. The controllers send 24v signals to the pump modules which are in effect relays. The modules then send 240v mains signals to both the boiler and to each of their own pumps. It's the 240v mains signal from modules to boiler that both need to be one way.

So diodes are for DC only. Thanks for that comment.

Any thoughts on what device I need to use? 2 incoming wires 240v mains into one wire but feed to be one way only so as not travel up the other incoming wire.
 

crutschow

Joined Mar 14, 2008
29,537
Any thoughts on what device I need to use?
It would seem you could add a relay from each controller signal to the boiler, which would isolate the signals and prevent the signal from one controller, affecting the other controller.
The relays would have 24Vac coils, and the contacts, in parallel, would provide a 240Vac signal (from the 240Vac mains) to the boiler.

Does that make sense?
 

crutschow

Joined Mar 14, 2008
29,537
Just look for a small SPST, SPDT, or DPDT relay with a 24Vac coil, and contacts that can carry 1A or more at 240Vac.
There are likely dozens to choose from, and any should work for you.

Here's an example.
 

ronsimpson

Joined Oct 7, 2019
2,022
I think there is a simple answer but I can't see your system.
A relay might be hard to wire in with out a socket.
1635861220763.png
Here is an example. You are looking for a 24VAC coil. Most relays like this will handle 24V or 220V on the contacts.
 

Alec_t

Joined Sep 17, 2013
12,746
the pump modules which are in effect relays.
I may have misunderstood your setup, but if they are relays, then if the contacts of either one are open I don't see how " when one module-to-boiler feed becomes live it would travel back up the module-to-boiler feed on the other circuit" ?
 

crutschow

Joined Mar 14, 2008
29,537
I don't see how " when one module-to-boiler feed becomes live it would travel back up the module-to-boiler feed on the other circuit" ?
It would appear that each module has only one outlet that goes to both the pumps and the boiler feed, so both pumps start for either module being on.
I think he wants to separate it so each module only controls its respective pump.
 

Thread Starter

mikemc

Joined Nov 2, 2021
11
Thanks for the replies. I think I'm getting warm but I'm not quite there.

The 2 controllers are 24v (They are plugged into the mains and have their own internal 24v transformer). But essentially I am dealing with the 240v switched outputs that go to the boiler. Those outputs are single live feed wires. It is these 2 separate 240v feeds that I need to interrupt with a one way device.

So I'm thinking I need 240v relays? I was imagining this device would have it's own live, neutral earth supply along with the incoming single wire live 240v signal. The signal would trigger the relay to pass the current via an outgoing single live wire to the boiler. So 4 wires in and 1 wire out.

I was also hoping the device might come as a "plug and play" item within it's own housing.

Thanks for your patience

Any thoughts?
 

Thread Starter

mikemc

Joined Nov 2, 2021
11
The zones are completely separate and will call for heat one at a time or both simultaneously. So that's the issue. When one is calling for heat I don't want the signal to travel back up the other "feed to boiler".

Crutschow's comments above are spot on
 

Thread Starter

mikemc

Joined Nov 2, 2021
11
I agree entirely.

I would absolutely get an electrician to do this but I would like to understand the possible configurations that may be available.
 
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