Two 'Circuits' in one MCB

[Silly Sausage]

Can't find the recent thread about this, but I've been looking at smoke detectors and got this from AICO under System Installation:

"• The supply for the mains powered alarms shall be taken from an electrically protected, regularly used local lighting circuit at the nearest source except for when the house is being rewired, then the supply
will be taken back to the consumers unit and connected to the same MCB as the local lighting circuit,
confirmation of connection method shall be provided from the Contract Administrator.
• All cabling shall be as specified in Clause 411 and shall be installed in accordance with the requirements
of BS 7671:2008 3rd Amendment 2015 (17th Edition IEE Wiring Regulations) and connected in accordance
with the manufacturers recommendations. "

So, there you have it!

 

[Rpa07]

Quick someone tell @Murdoch - he can go and have a lie down!

 

[telectrix]

so that advice bolloxes the idea of putting them on a dedicated circuit?

 

[Octopus]

so that advice bolloxes the idea of putting them on a dedicated circuit?

That went out of fashion about 10 years ago...

 

[telectrix]

That went out of fashion about 10 years ago...

probably the same time as me. still got 16th as a van reference.

 

[Silly Sausage]

so that advice bolloxes the idea of putting them on a dedicated circuit?

Looks like I'm getting another spare way in my CU after 14 years.
That'll be useful

 

[Octopus]

Anyway .......... its Westward10 who gets bent out of shape about this ......... not me.

 

[Ian1981]

We use Deta on new builds.
Manufacturers instructions still allow them to be on a designated circuit as long as nothing else is connected to it so the notion that they have to be installed on a local lighting circuit is rubbish

 

[suffolkspark]

Anyway .......... its Westward10 who gets bent out of shape about this ......... not me.

i spotted this thread and that was my first thought.... Can hear him coming like the jaws music....

 

[gof1]

Hi just been on an 18th edition update seminar, and smoke alarms did come up, the man (Darren Staniforth) did comment that smokes can be on a dedicated MCB, or on which I prefer a commonly used lighting MCB, ..........so its still just as grey as it always has been

 

[Octopus]

Hi just been on an 18th edition update seminar, and smoke alarms did come up, the man (Darren Staniforth) did comment that smokes can be on a dedicated MCB, or on which I prefer a commonly used lighting MCB, ..........so its still just as grey as it always has been

Just remember the NICEIC don’t write the rules .....

Good practice says they should be on a lighting circuit so they don’t get switched off ..... so your practice is better than his ...

 

[westward10]

Which good practice is this?

 

[Ian1981]

There’s no substantial evidence that one practice is better than the other.
Whether smoke detectors are on their own dedicated circuit or not it’s only opinion and not fact that smokes are better on a lighting circuit.
Both are viable options

 

[robd]

There's clearly arguements for both, the one about having the smokes on with a lighting circuit clearly eliminates the chance of the circuit being switched off so makes a lot of sense.

 

[Ian1981]

There's clearly arguements for both, the one about having the smokes on with a lighting circuit clearly eliminates the chance of the circuit being switched off so makes a lot of sense.

If people don’t want the smokes then they will remove the head and battery if need be regardless what circuit they are on.
I’ve even seen them covered up by a shopping bag.
If they are switched off then the battery will beep anyway

 

[robd]

If people don’t want the smokes then they will remove the head and battery if need be regardless what circuit they are on.
I’ve even seen them covered up by a shopping bag.
If they are switched off then the battery will beep anyway

Clearly you can't account for sabotage but that's up to them isn't it

 

[Ian1981]

Clearly you can't account for sabotage but that's up to them isn't it

Yes you can’t protect against stupidity

 

[Octopus]

I’ve seen countless rentals with smokes on seperate circuits .... switched off

That’s why I never place them on seperate circuits

 

[westward10]

Going to tell us where this good practice is.

 

[westward10]

Obviously not.

 

[Silly Sausage]

Going to tell us where this good practice is.

Arguably, it's subjective

 

[westward10]

Not actually guidance is clear in BS5839:6

 

[happysteve]

Not actually guidance is clear in BS5839:6

... which states that (for Grade D systems):

The mains supply to the smoke alarms and heat alarms should take the form of either:

1. an independent circuit at the premises’ 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 smoke alarms and any heat alarms); or
2. a separately electrically protected, regularly used local lighting circuit in which case there should be a means for isolation of the smoke alarm(s) from the lighting circuit (e.g. for maintenance)

For Grade E systems, (2) is recommended.

 

[markythesparky]

What does separately electrically protected mean?

 

[happysteve]

I'm not really sure. But there's a note underneath the above that says:

This does not imply that there need be separate electrical protection of the smoke alarm circuit; a single means of protection against overload or short circuit (e.g. a fuse or miniature circuit breaker) serving the entire circuit is acceptable.​

Perhaps they're trying to distinguish "proper" lighting circuits from those derived from (switched) fused spurs? Not really sure, though, sorry.

 

[markythesparky]

I would say that this means that it is acceptable to run smoke detectors on the same circuit as the lighting. But not two circuits, one for smokes and one for lighting, (2 cables) lumped together in one OCPD.

There should also be a means of isolating the smokes from the lighting, ie a switch or FCU.

In fact neither 1 nor 2 in the post before the last suggest that two cables in one OCPD is acceptable.

 

[happysteve]

There should also be a means of isolating the smokes from the lighting, ie a switch or FCU.

There is a further note (they just keep coming, don't they?!):

A number of manufacturers use a fixed base for the electrical connections, and the smoke or heat alarm can be readily removed by use of a tool operated release tab, etc.​