Room stat replacement

[Glenn Clark]

Hi All, I need some help.

I have jus bought a Horstmann DRT2 programable room stat to replace an old suntine stat. The new DRT2 on requires 2 wires and my old unit has 4. Ok 1 is the earth that the new unit will not require as its plastic. I have in the old unit thee following wires

1. Yellow (Heater) N. Blue (neutral)
2. Red (line)

the new unit says it only requires 2 wires but has 3 connections. Place heater to com an No or NC for the other wire. Can anyone give any advise on this. I am sure that 1 of these wires can be discarded and as the Horstmann website seems down I can't get anything from there

Thanks

Glenn

[Gary Cavie]

Stick the red wire into Com, and the yellow wire into NO. Make the blue & earth wires safe (choccy blocks & tape for example). I presume that the new stat is battery powered, and doesn't need a L&N to operate?

[Dave Liquorice]

I'd put 3. Red (line) to Com and 1. Yellow (Heater) to which ever of NO or NC is connected to Com when the stat is calling for heat. The N. Blue (neutral) is left unconnected but the end taped up or put into a single bit insulated terminal to stop it shorting to anything.

[Glenn Clark]

Yes it is battery operated. I did read on another group about not using the blue and the earth of course is not needed as the unit is plastic.

Thanks for your help

[Roger Mills (aka Set Square)]

More likely to be NC - but whichever one is connected to COM when the room temperature is *below* the temperature set on the stat.

Do *not* under any circumstances connect the neutral wire to anything - insulate it and make it safe. It was needed as the return for an accelerator heater in the old stat, but the new one doesn't have one.

Most stats have changeover contacts, which enable them to be used either for heating or cooling equipment by selecting the appropriate contact, but never

*both* at the same time. [If you connect neutral to the 'spare' contact, you'll have a direct short - and a big bang and flash - when the stat switches one way or the other.]

[Dave Liquorice]

If this is mounting on a metal back box, connect the earth to the terminal there.

[Ed Sirett]

We're geting this precise question more than once a week. Anyone up for the FAQ?

[Glenn Clark]

Ok so getting a little confused now. So what is the difference between the No and NC connections. The instructions do say that NO is the most common.

Thanks

[Owain]

The contact will be a changeover between Common and Normally Open (NO), and Common and Normally Closed (NC).

Thus the NO contact is a "call for heat" on a heating system and the NC contact is a "call for cold" on a cooling system.

(Usually. Unless I've got confused.)

Owain

[Dave Liquorice]

NO - Normally Open, no circuit to the COM terminal. NC - Normally Closed, circuit to the COM terminal.

I didn't state which to connect as I can't get my mind around the definition of "normal" in respect of a thermostat. Relays or contactors it's the rest, unergised state. You don't "energise" a stat...