Mains Smoke Alarm Wiring - Very Odd!!

[MFRacing]

Hi guys,

Just been fitting some new Nest Smoke/C02 mains powered alarms to replace my current mains pawer smoke alarms. Fitted the downstairs one with no issues, wiring as expected, i.e. Brown - Live, Blue - Neutral, Grey - Interconnect (not used on the new Nest alarms, so left disconnected). 2 of each to connect the other alarms in the house (i.e. ring)

Go upstairs to fit that one, and do it up as expected and no power to the alarm. I have 4 wires, Earth, Grey (Sleeved with Blue), Black (sleeved with Brown), and Brown. So I get my multimeter out and find:

Grey (Sleeved with Blue)
Brown 178v
Earth 36v
Black (Sleaved with Brown) - 0.55v

Brown
Grey (Sleeved with Blue) - 0.8V
Earth - 1.4v
Black (Sleeved with Brown) - 3.7v

Earth
Grey (Sleeved with Blue) - 36v
Brown - 240v
Black (Sleeved with Brown) - 0.5v

Black (Sleeved with Brown)
Earth - 100v
Grey (Sleeved with Blue) 0.5v
Brown - 128v

What the heck? So if I connect brown and earth I get 240v, and that would power the alarm!? I didn't see how the old upstairs some alarm was wired up (taken out before i got there, it was working fine though)

What do you think is going on? Maybe the wiring in the downstair one has affected the upstairs one? They are all connected on the same circuit (one MCB for all smoke alarms)

Can any one help?

Thanks
Matt

 

[Lectrician]

Disconnect everything on the circuit and start from scratch. You're over complicating things. Remove everything, and start to install your new ones. You should have one that has a two core cable feeding in, and three cores between the rest. If there is not one with just a two core, you can see inside your CU (most likely) which core has been used as neutral (the grey or the black).

 

[Iggifer]

You've wired something up wrong if they were all working correctly before. Go back to the first smoke and start again. Check the first smoke for a T+E & 3C&E.

This will tell you what to connect to which terminal, as you only need a live and neutral it should be super simple.

 

[MFRacing]

That's what I'm doing. The wiring is all Installed already though. Why can I not find 240 at the upstairs point apart from brown and earth?

Thanks for your help.

 

[Iggifer]

I would guess you've lost your neutral

 

[MFRacing]

You've wired something up wrong if they were all working correctly before. Go back to the first smoke and start again. Check the first smoke for a T+E & 3C&E.

This will tell you what to connect to which terminal, as you only need a live and neutral it should be super simple.

Yer that's my thinking. Gonna pull down the downstairs one now. That's working fine so not sure what could have gone wrong! Cheers

 

[MFRacing]

I'll report back in 30min or so!

 

[sparkwright]

It's odd at the first one to have brown, blue, grey. If you really have those colours there, I would expect some more wires too be floating around.

As suggested, turn off power completely, and disconnect everything and test it all out with a continuity tester.

PIctures will help enormously.

 

[Lectrician]

As I said at the start - Start again. From the start. You have dropped a connection somewhere. You are over complicating things by metering everything out.

 

[Lectrician]

Just to confirm. All old ones removed? There aren't some now with just wires hanging, not connected?

 

[MFRacing]

As I said at the start - Start again. From the start. You have dropped a connection somewhere. You are over complicating things by metering everything out.

Bang on! All fixed. A neutral had slipped out of the connection block in the downstairs alarm, re connected that and all good upstairs! Thanks again guys. I can have a beer now!

 

[ban-all-sheds]

I cannot for the life of me understand why it can be a good idea to use wireless interconnects instead of wired when the wired infrastructure is already there.

 

[Iggifer]

There is no good reason. More expensive and much more chance of them not all going off.

I would have gone with Aico myself but the Nest ones do have the advantage of telling you they've gone off when you're not there.

Let's just hope the OP doesn't have a VM Superhub or his house will burn to the ground

 

[MFRacing]

Just so you know guys they don't use the wifi network for interconnect. They talk direct to each other.

Loving the path light feature!

 

[JohnW2]

I cannot for the life of me understand why it can be a good idea to use wireless interconnects instead of wired when the wired infrastructure is already there.

In terms of 'instead', I would agree - but, as the OP now seems to have confirmed, I thought that the Nest ones did have wired interconnect.

However, I could see some theoretical merit in having wireless as well as wired interconnection, since it's not beyond the realms of possibility that wired interconnections could fail in the case of a major fire - but I don't know if any have that facility.

Kind Regards, John