Mains Smoke Alarm

[oldguy]

Can someone please confirm, I want to install 2 mains smoke alarms from the CU.

Do I just run a radial circuit in 1.5mm T&E, then 4 core for the interconnect between the two alarms?

Also what size MCB - 16A ?

thanks

 

[ban-all-sheds]

Do you plan to apply for Building Regulations approval, as you are legally required to do?

Do I just run a radial circuit in 1.5mm T&E,

"Just"?

What tests will you carry out on the circuit? What sequence will you do them in and at what point will you energise the circuit? For each test do you know what is being measured, why it is important, how you would carry out the test, and with what equipment, and what sort of results you would expect to get if everything was OK?

then 4 core for the interconnect between the two alarms?

Does the interconnect need that many cores?

Also what size MCB - 16A ?

Do the smoke alarms each consume 700W or more?

Given the installation method, and any other relevant de-rating factors, will 1.5mm² have an Iz ≥ 16A?

 

[bernardgreen]

MCB 6 amp adequate. 1 mm² would be OK

 

[Taylortwocities]

BAS is right, a new circuit from the consumer unit is notifiable.

Why do you not power the alarms from an existing lighting circuit?

This has two benefits:
1. As an addition to an existing circuit, the work is not notifiable
2. Should the circuit trip, you'll get a visial indication (the lights won't be working!)

 

[oldguy]

With the interconnect I meant 3 core & earth (brown, black, grey & earth).

The alarms are Kiddie KF10's.

Obviously I'm not qualified.....

So if I run (spur?) of the lighting circuit I 'just' need to run 1.5mm T&E to the first alarm then the 3 core & earth to the second alarm.....black used as the interconnect and the grey as the neutral?

And I can do this without it being notifiable?

 

[EFLImpudence]

So if I run (spur?) of the lighting circuit I 'just' need to run 1.5mm T&E to the first alarm then the 3 core & earth to the second alarm.....

1mm² T&E will be plenty more than adequate and save the planet 33% of the copper.

black used as the interconnect and the grey as the neutral?

It doesn't matter.
If your present light wiring is red and black, I would use black for neutral.
Whichever, it should be sleeved to indicate live and neutral.

And I can do this without it being notifiable?

Yes, no need to tell anyone.

 

[sparkwright]

Personally I would use black as the interconnect and grey as neutral.

There is more literature out there to suggest this is the way, and absolutely no literature to say it should be the other way.

The new harmonised black is not to be compared with the old colour wiring - they are two different systems.

And there's nothing harmonised about one group of electricians using grey as neutral, and another group using black.

 

[Iggifer]

I'm in the grey neutral, black interconnect camp too. Same with fans, SWA etc

 

[EFLImpudence]

Personally I would use black as the interconnect and grey as neutral.

Ok.

There is more literature out there to suggest this is the way, and absolutely no literature to say it should be the other way.

I shall have to write some equally authorative literature.

The new harmonised black is not to be compared with the old colour wiring - they are two different systems.

My comment was clearly applying to the unharmonized colours to which the op may be connecting.

And there's nothing harmonised about one group of electricians using grey as neutral, and another group using black.

Precisely - and as you will not know which was your predecessor, you will have to check, either way - unless, of course, one of them has a blue sleeve and one a brown.

It really is irrelevant.

 

[sparkwright]

Should be able to check which colours have been used, AND THEN FIND the 'correct' colours have indeed been used.

With the old colours, there was more than a 99% chance blue was the neutral, and yellow was interconnect/switch live.

In fact more than 99.999%.

As we all know,
red = brown
yellow = black
blue = grey

black = blue

So I see no other GOOD reason not to use grey as the neutral.

 

[EFLImpudence]

There is no red/blue/yellow.

However, I had forgotten:

So if I run (spur?) of the lighting circuit I 'just' need to run 1.5mm T&E to the first alarm then the 3 core & earth to the second alarm.....

So there will be no black to black connection - with old colours at light - so it doesn't matter.

 

[eveares]

Also what size MCB - 16A ?

MCB size 3A if you can get hold of one, if not then 6A. I have not seen a domestic smoke alarm what is rated at 3.68Kw. As others have said, adding a new circuit (and thus a MCB) is notifiable work.

As others have said:

Brown = Permanent Line
Black (Sleeved Brown) = Interconnect
Grey (Sleeved Blue) = Neutral
Bare Copper (Sleeved Yellow striped green) = Earth & CPC

It doesn't matter.
If your present light wiring is red and black, I would use black for neutral.
Whichever, it should be sleeved to indicate live and neutral.

Black and Brown should not be used for neutral!; Always use Blue or Grey sleeved blue for neutral. That way people wont get confused between old and new neutral colours, and end up thinking black in neutral when in fact it is a live conductor.

 

[EFLImpudence]

Firstly, the regulations merely state that conductors be identified by the appropriate colours or alphanumeric.

Black and Brown should not be used for neutral!

Well, that refers to the identification markers, not the conductor insulation.
Non-harmonized colours did/does use black for neutral and there is plenty left. Do you sleeve these brown and blue?

Always use Blue or Grey sleeved blue for neutral.

Not quite - always sleeve neutral with blue.

That way people wont get confused between old and new neutral colours,

I don't get confused.
If sleeved correctly I will know - but still check; I wonder why.
If not sleeved, I simply don't know what the previous person has done; that is not confusion.

and end up thinking black in neutral when in fact it is a live conductor.

The same can be said for the grey.


Answer this:
A customer removes an extractor fan, cannot fit the new one, calls you.
You arrive,

A) find hole in wall with red/yellow/blue wires with no sleeving.
(Did anyone ever sleeve the blue with black?)
Do you connect red to L, yellow to SL and blue to N without checking?
If not, why not? After all, Live is red, Neutral is blue and SL must be yellow.

B) find hole in wall with brown/black/grey wires with no sleeving.
What's the difference?

 

[ban-all-sheds]

If not sleeved, I simply don't know what the previous person has done; that is not confusion.

There will come a time when the previous person is you, and that will be confusion.

 

[EFLImpudence]

...but no one will ever know when that will be.

I really don't think confusion is the right word - or it shouldn't be.
Perhaps - uncertainty - so when will everyone be certain?

Grey is not a recognised colour to denote neutral.