Strange(?) wiring in modern house

fortress · 21 Nov 2011

We've moved to a house which was only built a couple of years ago. The room thermostat got "lazy", so I've been trying to replace it. But I can't suss out the wiring at the stat.

It's no good looking at the boiler-end because all wires seem to go through a 12-terminal wiring center in the airing cupboard, which connect to a Drayton 3-port valve plus a Honeywell 2-port one (and cylinder stat of course). It's a real bowl of spaghetti there.

Apart from Earth, there 3 wires coming out of the wall at the stat: Brown, Light-grey sleeved Blue, and Dark-Grey sleeved (Dark) Brown.

My voltmeter needs replacing so I'm not able to use that. So I'm really hoping these wires are common in modern UK houses, so someone can explain them? Please! Is D_Hailsham around?

Corgigrouch · 21 Nov 2011

Blue wire or blue sleeve = Neutral
Brown or Brown sleve = Live.......... Simples

Count yourself lucky that they bothered to identify the wires...

namsag · 21 Nov 2011

One brown is live in one is live out if you mix them up it will just stop the heat anticaptor within working .
But depending on what stat you replace it with this may not be an issue

fortress · 22 Nov 2011

OK sure, the colours ought to mean:-

Brown: Live
Dark Grey sleeved Dark Brown: Switched Live
Light Grey sleeved Blue: Neutral

But what I was hoping was that you'd all say "That's what you'd expect to find in a modern house, it's standard to first-fix a cable with Brown, Light Grey, and Dark Grey (plus Earth). And it's normal to find a wiring centre with umpty terminals looking like a bird's nest (even if neatly done) -- to manage the programmer, roomstat, and two valves: a 3-port and a 2-port, quite typically by Drayton and Honeywell.

I was also hoping someone could say definitely that Live comes from the programmer, Switched Live goes back to the boiler/pump, Neutral is just mains neutral.

There must be some guys on this forum who've worked on 21st century houses?

D_Hailsham · 23 Nov 2011

fortress said:
I was also hoping someone could say definitely that Live comes from the programmer, Switched Live goes back to the boiler/pump, Neutral is just mains neutral.

You are nearly right.

Switched live, in your case goes back to the 3-way motorized valve white wire.

If you take the lid of the junction box and find the white wire among all the spaghetti, you can determine which coloured wire is connected to this. The rest then falls into place.

Many modern thermostats do not require a neutral.

fortress · 23 Nov 2011

Thank you so much Mr Hailsham. That's what I needed, Clarity.

The fitted stat which has "gone lazy" is a Drayton RTS1. I suspect the original might have been an RTS4 (which looks identical I believe) because the boiler is a combi (Glow-worm Ultracom 18sxi). I've now determined 2 things:

1. The RTS1 does need the Neutral connected.
2. The N doesn't come straight from the mains. When a digital stat with no N terminal failed to work I tried an experiment: I connected the neutral, i.e. the light grey sleeved blue, to the Earth in the cable. When I switched on the house 13A power CB tripped.

So back to the lazy RTS1 for now!

mikely · 23 Nov 2011

fortress said:
2. The N doesn't come straight from the mains. When a digital stat with no N terminal failed to work I tried an experiment: I connected the neutral, i.e. the light grey sleeved blue, to the Earth in the cable. When I switched on the house 13A power CB tripped.

If you connected neutral to earth, you would expect an RCD or RCBO to trip, which it sounds like it did.

With a digital stat that does not require a neutral, you would expect to connect to the brown (live) and brown sleeved (switched live) wires only. Are you saying that did not work?

D_Hailsham · 23 Nov 2011

fortress said:
The fitted stat which has "gone lazy" is a Drayton RTS1.

What do you mean by "gone lazy"?

The N doesn't come straight from the mains.

I would expect the neutral to connect back to the junction box, to a terminal which had several other neutrals, e.g from the motorized valve, connected.

matt1e · 23 Nov 2011

fortress said:
But what I was hoping was that you'd all say "That's what you'd expect to find in a modern house, it's standard to first-fix a cable with Brown, Light Grey, and Dark Grey (plus Earth). And it's normal to find a wiring centre with umpty terminals looking like a bird's nest (even if neatly done) -- to manage the programmer, roomstat, and two valves: a 3-port and a 2-port, quite typically by Drayton and Honeywell.

There must be some guys on this forum who've worked on 21st century houses?

All of the above is 20th century technology never mind the 21st!!

fortress · 2 Dec 2011

@D_Hailsham: "Gone lazy" is what seems to happen to all roomstats eventually, in my experience. I mean the gap between switching on and off gets wider. Having set a stat you shouldn't have to touch it again - but after a like a year you start finding the home has gone chilly so you have to up the stat till it clicks then turn it back a little. You just shouldn't have to do that.

@mikely: Correct.

matt1e · 2 Dec 2011

fortress said:
Switched Live goes back to the boiler/pump,

It may or may not, It depends on the system

Whitespirit66 · 2 Dec 2011

fortress said:
I believe) because the boiler is a combi (Glow-worm Ultracom 18sxi).

No, it ain't.

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Strange(?) wiring in modern house

namsag

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