Neutral on room stats

[Masood]

Some have it, some don't, but can anyone please explain why? What does it do? As the stat is a simple on/off switch.

I fit Honeywell two-wire ones normally so I've never really had to think about it except when replacing stats like-for-like but would like to understand the principle..

Cheers!

 

[DaveTidy]

The neutral feeds an anticipator on the room stat (see individual diagrams for each stat).

This helps the room stat anticipate when the set temperature is reached so there is very little delay e.g. the room seems to go hot then cold then hot then cold; it just helps to prevent lag when temperature is reached or drops.

Seen a lot of people snip the neutrals off over the years!!

 

[Masood]

The neutral feeds an anticipator on the room stat (see individual diagrams for each stat).

This helps the room stat anticipate when the set temperature is reached so there is very little delay e.g. the room seems to go hot then cold then hot then cold; it just helps to prevent lag when temperature is reached or drops.

Seen a lot of people snip the neutrals off over the years!!

Cheers Dave! So is the anticipator an electronic component?

 

[doitmyself]

So is the anticipator an electronic component?

An anticipator is used in mechanical stats which rely on the expansion and contraction of a temperature sensitive bi-metal element to open and close the switch. Without it the temperature difference between on and off would be too great.

It's just a small resistor which gets heated up when the thermostat is closed. The inside of the stat therefore warms up faster which means the stat will turn off sooner, thus reducing the on/off difference. If the Line In and Switched Live connections are swapped, the anticipator is permanently heated, which means it is no longer effective.



Modern two-wire thermostats use a temperature sensitive resistor (thermistor) to measure the room temperature. so a neutral connection is not required.

 

[joni os]

Thanks for clear explanation. I too was always confused by purpose of extra wire.

 

[Roger Welton]

The above explanation is correct for some stats, however some (Drayton) use a small electronic circuit and relay to switch the boiler so need the neutral for this to work. (This is why they dont cick when the power is off)

 

[Ch4 plumbing]

I naively thought if you used a neutral it made the stat more accurate?

 

[Roger Welton]

I naively thought if you used a neutral it made the stat more accurate?

on those with a anticipator it does (i think honeywell say +- 2deg without and .5deg with)

 

[Ch4 plumbing]

So not too far off the right path thanks.