Mains Smoke Alarm

[Taylortwocities]

560.7.1?

560.7.1 deals with many types of safety services. Some of which obviously need a separate supply. (e.g. Fire pumps, fire rescue service lifts, etc)

But we are talking about domestic smoke alarms here, typically LD3. In BS 5839-6 2004 , and the manufacturer's instructions, the following is stated:

The power supply for the Alarms should be derived from the public electricity supply to the dwelling. The mains supply to the Alarms should take the form of either:

(a) an independent supply at the dwellings main distribution board, in which case no other electrical equipment should be connected to this circuit (other than a dedicated monitoring device installed to indicate failure of the mains supply to the Alarms);
or
(b) a separately electrically protected, regularly used local lighting circuit.

The majority of home mains smoke alarms are powered from a lighting circuit. Both hard-wired interlinked alarms and those using the Radiolink-type bases.

 

[EFLImpudence]

at least they would know that grey would most likely be the neutral.

That is the salient point.

"they would know that grey would most likely be the neutral"

So they wouldn't know - and never will.

 

[ban-all-sheds]

560.7.1 deals with many types of safety services.

Yup.

But including, unqualified by Class A, B, C etc, "fire detection and alarm systems", so including domestic smoke alarms.

And 560.7.1 is unequivocal in what it says.

 

[eveares]

Let me see if I've got this straight:

You're positing a scenario where someone is cutting into a cable without having found either end of it, and therefore without knowing whether there is a neutral present, and without having been able to test for dead?

Yes - Well sort of; imagine that 3 core + CPC is feeding an appliance such a timer fan what you know must have a neutral but you don't have direct access to either end of the cables terminations. Now you need to install a second fan and only have access to the 3 core + CPC.

While of course any of the cores could be neutral, it is most likely to be the grey one and thus without being able to prove what core was neutral, if one had to unwisely guess and take a chance on what one would be neutral, you would assume it was the grey one due to grey being most typically used for neutral in 3 core.

While true that table 51 of BS7671 or reg 514.3 - 514.9.1 does not mention about what each core in 3 core wire should be used for, I am only going by a Nappit certified electrician who once told be that black core in 3 core must not be used for neutral.

 

[PBC_1966]

Yes - Well sort of; imagine that 3 core + CPC is feeding an appliance such a timer fan what you know must have a neutral but you don't have direct access to either end of the cables terminations. Now you need to install a second fan and only have access to the 3 core + CPC.

If you can't access either end of the existing cable in order to at least attempt to trace it, how can you be sure that the cable you're about to cut into is, in fact, the one you want?

 

[EFLImpudence]

While true that table 51 of BS7671 or reg 514.3 - 514.9.1 does not mention about what each core in 3 core wire should be used for,

Right.

I am only going by a Nappit certified electrician who once told be that black core in 3 core must not be used for neutral.

Wrong.

That's how these things start.

 

[eveares]

Wrong.

That's how these things start.

Well you tend to trust and re-iterate what qualified people tell you.

Still we all agree on that a Brown, Black or Grey wire that is used for neutral should be sleeved blue and not left as brown, black or grey right?

 

[sparkwright]

Right, back to basics.

First of all, in an old colour 3 core+E, with red, yellow, blue, how LIKELY would it be that the blue would be used for neutral?

 

[sparkwright]

OK.

Highly likely, IMO.

 

[sparkwright]

Ok.

If an old 3 core+E has a blue in it, what is the EQUIVALENT colour to this in a new, harmonised 3 core+E?

 

[ban-all-sheds]

Why don't you just cut to the chase and tell us why you think that matters?

 

[EFLImpudence]

If an old 3 core+E has a blue in it, what is the EQUIVALENT colour to this in a new, harmonised 3 core+E?

There isn't one.

The fact that blue happened to be one of the three core colours here and is what Europe use for neutral is just a coincidence.

What would be the position if it were the other way round?
That is, Europe changed their colours to Red and Black and Red, Yellow and Blue.

 

[ban-all-sheds]

Yes - Well sort of; imagine that 3 core + CPC is feeding an appliance such a timer fan what you know must have a neutral but you don't have direct access to either end of the cables terminations. Now you need to install a second fan and only have access to the 3 core + CPC.

So you're going to just assume guess that it is dead.

While of course any of the cores could be neutral, it is most likely to be the grey one and thus without being able to prove what core was neutral, if one had to unwisely guess and take a chance on what one would be neutral, you would assume it was the grey one due to grey being most typically used for neutral in 3 core.

No, you would stop and not continue until you had got access to the terminations of the existing cable.

Guessing does not count as exercising reasonable skill and care.

Guessing does not count as good workmanship.

Guessing is not something which is done by skilled or instructed persons.

Guessing is not allowed.

 

[ban-all-sheds]

If an old 3 core+E has a blue in it, what is the EQUIVALENT colour to this in a new, harmonised 3 core+E?

There isn't one.

Yes there is - it's grey.

FOR L3.

But there was never a N conductor in red/yellow/blue cable, just as there isn't one in brown/black/grey.

 

[EFLImpudence]

Fair enough.

Is that where lies the belief that Grey is Neutral?