Contactor wiring with Nest thermostat

[steve1906]

Hello, I'm trying to get a contactor to work with a nest thermostat to activate an oil filled heater rather than a boiler.


I wired permanent live and neutral to the two poles at the top of the connector (1+3), switched outputs to the bottom (2+4) then the common and demand lines from nest to A1 and A2.


There's a click from the contactor when demand is called but no voltage across the poles so I've measured and it appears to be a dry heating switch which obviously isn't activating the contactor properly.


There's a wiring diagram with the nest to link live to the common terminal if I want a wet (mains voltage) connection so if I did this I've now got a line from heating demand that would presumably go to A1, but what would go to A2 to complete the circuit?


The contactor is the BG one from Screwfix that requires mains voltage on the coil.


Thanks for any advice!

 

[DefyG]

requires mains voltage on the coil.

What's needed to complete the circuit if you already have a live 'mains' conductor to one side of the coil?

 

[steve1906]

Contactors are new to me and I'm treating it as a relay in principle but what you're saying suggests I just need to energise one side and that will work? So I'd have perm live and neutral one side, switched on the other, then say call for heat on A1 which would be the mains voltage call from the thermostat and nothing on A2... It just seems a bit alien to me having nothing on A2 but you're saying that's fine?

If that is the case I can't believe how simple this is, I was thinking having to find the neutral from somewhere! You'll have made my day if it is this simple as I've spent hours reading about contractors before posting here.

 

[James]

May I suggest that you post a wiring diagram of what you are suggesting?
and yes, a contactor is just a big relay.

 

[steve1906]

It's a bit rough and ready but you can see from the image I have a 230v call for heat going into A1, nothing into A2 (which is confusing me how the coil will work with only one side of it being connected), then perm live and neutral into 1,3, switched live and neutral coming out of 2,4 which will then go to a socket serving the single room plug in oil heater.

 

[DefyG]

having nothing on A2 but you're saying that's fine?

I was thinking having to find the neutral from somewhere!

No I wasn't saying that was fine, the circuit would not be complete!

I think you've answered your own question, yes you need a neutral to complete the circuit.

 

[steve1906]

If I pinched the neutral from 2 and linked it to A2 then I'll be in business?

 

[James]

If I pinched the neutral from 2 and linked it to A2 then I'll be in business?

On your drawing, N is connected to terminal 2, not 3
But yes a2 needs connecting to N

 

[steve1906]

I think it was too early yes I meant 3 not 2, but great I'll give that a whirl and thanks.