Danfoss "volt free" thermostat

[Neon Vagabond]

hi, got a new job, doin boilers. A wee bit out of my element

Got a vokera combi to wire, i understand almost everything apart from the thermostat.
Its a danfoss RET230 VF2.
what do i need to wire this?
Wire into Live and neutral terminals on the stat?
Wire into number 2 and 3 on the stat?
Or does it need both a feed and neutral and also a switch wire?
This is one of the "volt free" species which i do not fully understand
If its volt free why does it say 230V on the package

 

[stef]

Probably, it still switches 230V.

 

[Octopus]

Call Danfoss technical - they are far better than the instructions in their boxes.

 

[MarkieSparkie]

The main characteristic of a volt-free contact in this context, is that it is fully floating - not referred to earth or any supply voltage, AC or DC.
They are usually derived from relay contacts or similar, and can be N/O, N/C or C/O. In this case the thermostat may switch these either by bi-metal strip or similar mechanical system, or via a thermistor controlled electronic circuit driving a relay coil.
The opposite of a volt-free contact, is where the output of semiconductor device switches the load directly, with no isolation and the device electrode voltages are present on the 'contacts' and may effect the switched equipment. If the semiconductor device is a transistor, the output (contacts) may be described as "Common Emitter", "Common Collector", "Common Source", "Common Drain", "Open Collector", "Open Emitter", or similar.
Solid-state relays are now becoming more common, in which they incorporate voltaic (or galvanic) isolation - usually via an opto-isolator - these can also represent an electrically-floating set of relay contacts.

 

[Neon Vagabond]

right so the twin and earth at the original room stat should be fine?
I just struggle to get my head around how it actually works if theres no power being supplied to the unit.
Can anyone reccomend any book that might give me a full working idea of how central heating systems work.
If im gonin to be doin this i suppose i better know the ins and outs of it

 

[snowhead]

right so the twin and earth at the original room stat should be fine?

NO, you need Live and Neutral (+earth) to power the electronics and a pair for the boiler control.

Most Thermostats have been volt free for years, just means the contact isn't connected to anything else in the stat. Same thing in programmers.

I just struggle to get my head around how it actually works if theres no power being supplied to the unit.

See above it does need power. Some Stats are battery powered, but not the one you refer to.
The Live can be from the boiler IF the boiler is using 230v on the control circuit.

 

[Amp David]

Glow worm combis have volt free stat wiring, L and N terminal on the boiler only, 24 volt.

You wouldn't use a 3 core and earth for that.

 

[Neon Vagabond]

duno where my post has gone.......
Yes thanks snowhead i understand better now, i'll just run the mains off the spur to stat and then get my switch wires over....
i'll be looking into this further, till i get my head around it