Electronics > Beginners
Parallel mains switches for boiler control
paulca:
I have a new boiler which has a 7 day timer stuck on the wall in the boiler cupboard.
I want to additionally add a relay to control it independently.
Previously with my older boiler I put my relay inline with the day timer, so the day timer had to be on for the relay board (SOnOff) to have power. The relay was setup to go ON when it was powered and this provided transparent control using the 7 day timer, should I need it.
I'm not sure I want to do this again. I want to run the 240V mains output the boiler provides and send the "Live return" back for the heating control from my relay. This would mean I have two return paths for the "live return", one from my relay, one from the 7 day timer.
In theory there shouldn't be an issue if I have a live return from both the 7 day timer and an additional relay. If one relay is off and the other on, it will just energize the disconnected pin on the other relay. If both relays are on then both relays will be at "live" / line voltage, but that's fine too.
Am I missing anything here? So two parallel circuits:
Mains Out -> 7 day timer -> heating LR
Mains Out -> Smart Relay -> heating LR
Note, the SOnOff is the more recent version after CE certification and it will (I hope) be mounted in a fire safe box on the wall with proper strain relief glands to prevent accidental exposure to the mains should it get knocked off the wall etc, though unlike as it's in a cupboard. Should also help contain any potential fire if it were to fail.
paulca:
I could get unlucky and one of the two relays switches it's output to neutral when it's off, that would then blow the fuse.
Maybe putting the two in series again is the safer option.
Docara:
Hi
Could you explain a little more why and what you are trying to do.
Are you trying to have an additional control to turn the boiler on when required? If so get a new timer with a 'Boost' switch at least then you could parallel up the switch. The beauty of this is with all the boost controls I have dealt with 1 press = 1hr, 2presses = 2hr and up to 3 then off in a cyclical manner.
mikerj:
Providing both the timer and your extra relay are both SPST devices (i.e. they both either make or break the circuit rather then e.g. switching between live and neutral) then paralleling the switches is fine.
paulca:
--- Quote from: mikerj on November 22, 2019, 03:11:41 pm ---Providing both the timer and your extra relay are both SPST devices (i.e. they both either make or break the circuit rather then e.g. switching between live and neutral) then paralleling the switches is fine.
--- End quote ---
Yes, this is what I thought, but one of the switches (the 7 day timer) is a sealed unit and asides testing for continuity to neutral while it's off I can't really test this.
I figure it's quite unlikely they have DPST switches which switch the output to neutral, but the results if they do would be a bit nasty. The last timer switch I had, found the manual for it, actually switched the live between two outputs so you have Live out ON and Live out OFF. Given that these are all meant to mount to an industry standard back plate, it's likely they all switch the same way.
I'll see if I can google up the manual for this one and maybe do some careful testing. Slightly annoyingly the boiler is on the main plug ring circuit, so to make it safe I have to take out most of the house power :(
Navigation
[0] Message Index
[#] Next page
Go to full version