Lights off a Fire Alarm

[Steventown]

Can I wire in my lights (2core) to the fire alarm (3core) if so does blue go to black or grey? Or have I completely not understood the 3 core wire, which is frankly quite likely!

 

[EFLImpudence]

Can I wire in my lights (2core) to the fire alarm (3core) if so does blue go to black or grey?

Could be either.

Or have I completely not understood the 3 core wire, which is frankly quite likely!

Not really, there is a feeble attempt to get us to use grey for the neutral but as no one ever knows what the previous person has done, it is completely pointless.

Whichever it is, it should have a blue sleeve, which may be present at one/both of its ends and you should do in the junction box.

 

[John D v2.0]

What I want to know is what the other wire is for? Is it a pull up so the alarms can set each other off?

 

[Steventown]

Thanks, so if I get it wrong, I presume my fire alarms will go off, and if I get it right, all will be well!?

 

[OwainDIYer]

What I want to know is what the other wire is for? Is it a pull up so the alarms can set each other off?

It's for interlinking the alarms, but may not be as simple as a pull-up to 240V. Misconnecting 240V to it, even through a lightbulb, may render your alarms temporarily inoperative or kill them totally.

 

[Spark123]

I'd say it will kill them completely, iirc the interconnect is only a few volts DC wrt the neutral conductor.

 

[Steventown]

Right, so get my hands on a voltmeter to find which is which, thus avoiding blowing up my fire alarms...

 

[John D v2.0]

I'd say it will kill them completely, iirc the interconnect is only a few volts DC wrt the neutral conductor.

Would it be right to connect a DC ELV circuit to the neutral? I'm going to do some research later as this is interesting

 

[Spark123]

I don't see why not, if it wasn't OK then they wouldn't interconnect off the backup batteries when mains fails.

 

[John D v2.0]

Good point, and I suppose as long as the ELV side is insulated for LV there wouldn't be an issue.

 

[Risteard]

Can I wire in my lights (2core) to the fire alarm (3core) if so does blue go to black or grey? Or have I completely not understood the 3 core wire, which is frankly quite likely!View attachment 106087

The correct answer (which you don't appear to have been given yet) is that you clearly need an Electrician.

 

[sparkwright]

The correct answer (which you don't appear to have been given yet) is that you clearly need an Electrician.

I don't think that's a very good answer.

The op has shown some reasonable knowledge for a DIYer, and is asking the right questions.

Mind you, the obvious thing to do would surely have a look inside one of the detectors to find out which colours have been used.

Of course, pre-harmonisation, when it was red, yellow, blue, there was never this confusion between yellow and blue.

And there shouldn't be any confusion now between black and grey.

We know that
Red = brown
Yellow = black
Blue = grey

So why people insist on using black as the neutral is beyond me and shows total ignorance.

But there you go.

 

[Risteard]

I don't think that's a very good answer.

The op has shown some reasonable knowledge for a DIYer, and is asking the right questions.

I have to say that the photo provided and the questions asked do not inspire me with confidence that he has sufficient knowledge or experience to carry out this work, and as such my answer was the correct one.

So, to reiterate, the OP needs an Electrician. That is the only correct answer to his question.

 

[333rocky333]

In the early days a lot of people used black as neutral often sleeving the brown red, there was not much info regarding 3 core colours for single phase available.
I have seen many early boards like this, some even mixed with circuits done the now correct current way
Similar aproach to how when R Y B was available people asociated Blue with neutral, though I dont recall any tech data to confirm this.
Blue was only ever a neutral in single core flex, never in SWA, black was Neutral
I think in almost every case now, you need to verify the ends and if feasible correct them to the current standard

 

[sparkwright]

When harmonised cable came out in 2004 there was LOADS of information informing us which colours to use - in 3 phase situations, and regular single phase use - including 3 core and earth cables where a neutral may be included.

There were leaflets, key rings etc with it all shown.

In the case of a 3 core and earth cable, one barely even has to be told - because it's so obvious. Look at the structure of three core and earth cable. From side to side one could say the sequence is Red, Yellow, Bare earth, Blue.

A new cable goes Brown, Black, Bare earth, Grey.

So that alone shows us grey should be neutal, if we used the blue and the neutral before. And people did always use the blue for neutral.