Wiring a Nest Protect

[Temmy]

Hello.

I want to replace my existing smoke alarm with a Nest Protect.

I don't however understand the cable feeding the old alarm and how that would work with a Nest Protect.

If I can't get my head around it I will of course get an electrician to do the job, because electrical safety isn't to be gambled with. But I'd like to try and understand.

Here's the cable:

Here's the wiring diagram for the Nest Protect:

My understanding so far is:

- What I have is a 3 core & earth cable. Is that correct?
- The black wire is interconnect and won't be used, so needs to be terminated.
- The bare wire is earth and won't be used, and will need to be sleeved(?) and terminated.

Basically I want to know how that wire translates to the wiring diagram.

 

[EFLImpudence]

- What I have is a 3 core & earth cable. Is that correct?

Yes.

- The black wire is interconnect and won't be used, so needs to be terminated.

Probably. Do you know that from looking at the other alarms?

The bare wire is earth and won't be used, and will need to be sleeved(?) and terminated.

Yes.

Basically I want to know how that wire translates to the wiring diagram.

It means you have to connect Live and Neutral to the Nest.

You will need to test to determine which wires are L & N.
Presumably Brown will be L.

 

[Temmy]

Figured it out.

First lesson of today; take a photo before you disconnect something to know what all the wires were doing.

Luckily there was another smoke alarm upstairs. By looking in there I can see what all the wires are doing:

We can see the power coming into this one, but we can also see that brown is is live, black is interconnect, and grey is neutral.

 

[EFLImpudence]