Quick Consumer unit query

[Stephen H]

Hi,

I have 12 mains interlinked smoke detectors, each has battery back up. This is currently wired into a single 6A MCB at the CU.

I also have 4 new mains interlinked battery backed up carbon monoxide detectors. This is awaiting connecting up to the CU.

I also have a new mains intruder alarm with 12 PIRS. There are two spare

24 hour zones on it. I plan to use these with appropriate interfacing to link into the smoke detectors and the CO detectors. This alarm again is awaiting connecting to the CU via a fused unswitched unit

The alarm has battery backup and an autodialler and internet connectivity via broadband.

Is it OK to wire the power for all three subsystems into the same MCB at the CU or have they all got to be on 3 seperate MCB's? if necessary I can wire all three to a junction box and then run one cable from this to the 6A MCB?

The interfacing in question is simply volt free changeover relay contacts on one of the CO detectors and on one of the smoke detectors.

My reasoning is that its OK to wire all three into the same MCB is for four reasons:

1. Everything has battery backup throughout, so the whole system is still functional for soem considerable time with no mains power shoudl the MCB trip.

1. It avoids having different parts of the interlinked system powered via different MCBs and hence confuse future maintenance staff when servicing the whole system.

2. The intruder alarm will signal a mains failure via an indoor buzzer and signal out via the autodialler and the broadband internet, which would not be the case if it was smoke detectors only, as they would just switch to battery and only start beeping when the batteries run low.

1. There is signalling between the three parts via the volt free changeover contacts and so the system is interconnected anyway, and its bad practice to have the system fed power from more than one common point.

Regards,

Stephen.

[John Rumm]

You can wire whatever makes sense to you and future maintainers. So long as the cable you use is adequately fault protected by your MCB of choice, then there is nothing preventing all the alarm related systems being powered from one MCB. As you note later it might be less logical to split the subsystems between circuits.

[Dave Liquorice]

Four seems a bit OTT but perhaps you have four rooms with wood burners and/or boilers in?

Six of one half a dozen of the other...

As you say everything has battery back up so having to switch everything off to work on any single sub-system is no degradation of safety. Other than running the batteries down. Are these batteries replaceable or are the detectors single use, replace whole thing when battery is flat/knackered?

Bear in mind that the smokes/CO and alarm systems are actually isolated from each by virtue of the volt free relay connections. I'd be tempted to have the alarm on one MCB and the detectors on another, possibly two depending on if the detectors share the same cable or have their own cables.

The alarm signalling mains failure is a good feature but mains failure on the detector circuit(s) could be simply done with tell tale neon(s) in a place you pass often. Having said that our Ei mains/battery backed/interlinked smoke/heat detectors have green tell tale built in.

[Nitro®]

How can it 'signal out via the autodialler and the broadband internet' if there is a mains failure? Am I misunderstanding something?

[charles]

battery power?

[John Rumm]

I assume the autodialer will signal via the mobile phone network and a sim card. The broadband is a separate path.

[Dave Liquorice]

Alarm has battery backup. Analogue phone lines work without mains power =

or it could use the mobile networks. The latter might not be very reliable in the case of a power outage as very few cell sites have backu= p power. If the power cut affecting the alarm is also affecting the local =

cell site...

The broadband is a bit trickier if the ADSL modem and, if required, network switch aren't on a UPS. Of course there could be alarms with ADS= L modems in but I can't see that being very practical.

[Stephen H]

Perhaps I should have phrased my question better.

I had been led to believe that smoke detectors should have their own MCB or RCBO at the CU rather than say being wired via a FCU on a 32A ring main circuit. The reasoning being that if a fault developed on the ring main and tripped an RCD or a MCB, that the smoke detectors did not lose power.

The question really was that is it within the regs to connect an intruder alarm into the same MCB as that powering the smoke and CO detectors?

Stephen.

[Stephen H]

i have a wood burner in lounge, gas boiler in kitchen and a chimney stack in the main bedroom and in the loft. (in case the chimney leaks fumes) hence four interconnected.

All 12 smoke dets have removable and hence replaceable 9v PP£ batteries.

The CO detectors have rechargeable batteries and are sealed units and will also warn when the CO detector needs total replacement in 10 years time as that apparently is the lifetime of the CO sensor element.

At the moment, a single Twin & Earth cable goes to the 1st smoke det from CU, then its 3 core cable to the other 11 smoke dets in daisy chain fashion. Then its twin & Earth from the last smoke det to the 1st CO det, then its 3 core to the other three CO dets. I can pick up alarm power from the last CO det (which is in loft) to power the alarm panel.

The CO dets and Smoke dets are from different manufacturers (Kidde and Dicon respectively) and hence cannot be interconnected for signalling, but they can be connected via power.

I have green tell tales on all my smoke dets and on the CO dets.

The alarm panel has an onboard POTS autodialler, and there is also an option to add an Ethernet module (for communicating to internet) and an option to add a GSM/GPRS module for SMS text messaging.

[Stephen H]

The alarm autodialler is integral to the alarm panel, It also supports the addition of an ethernet module (for internet access) and a GSM/GPRS module for SMS text messaging, which will be powered via the alarm panels lead acid battery during power failure.

I am deaf so the auto dialler can phone my hearing wife, and teh GSM/GPRS module can text my mobile phone or the ethernet module can email me.....

[Stephen H]

the autodialler is a POTS dialler. But as mentioned earlier, there an ethernet module available and a GSM/GPRS module for the alarm panel I have.

[Stephen H]

Yes, landline phone exchanges have robust power due to teh requirements to support at least 999 calls.

I do take your point regarding mobile phone networks though.

I will have an UPS on the Cable and ADSL modems as well as on the 48 port switch (i have CCTV as well)

[ARW]

All via one MCB should be OK - and ideally not sharing a RCD with a socket circuit.

[Stephen H]

As part of the CU replacement, I will be using RCBOs on each circuit.

The main reason for using RCBO's is to minimise the impact on the rest of the house should a circuit trip. The final circuit list looks like going to be as follows along with the appropriate reasoning

6A ground floor lights 6A 1st floor lights & loft lights (did wonder about seperating the two in case I convert loft at a later date) 6A Outside lights (if fault develops outside, it does not affect rest of lighting in house) 32A Grd & 1st floor Left hand side sockets 32A Grd & 1st Floor Right hand side sockets 32A Loft sockets (this is going to be my servers, network switches etc and TV/Satellite/Radio headend room so want high availability, and do not want faults elsewhere taking out computers and causing data corruption.) 32A Cooker 6A Boiler (this boiler has automatic frost protection built in, so need high availability power to minimise burst pipes and don't want faults elsewhere taking out boiler) 6A Outside sockets & garage sockets (if fault develops, it does not affect any sockets within house) 6A Smoke, CO detectors and intruder alarm. On its own RCBO so not affected by faults elsewhere.

That's a total of 10 (or possibly 11 if I split one of the lighting circuits) RCBO's

Also If I decide to have solar PV, there will be two spare ways in the new CU for this and for a 2nd 32A ring main if I convert loft into living accommodation and keep servers & headend on its own ring main.

constructive suggestions and comments most welcome.

[Tim Watts]

As they are interlinked, they should all be on the same MCB.

The "usual way" is you wire your smoke alarms into a lighting circuit that would be notices immediately if it failed - say the one doing the hall by the main door.

Can you wire your intruder alarm into this too?

Or put the intruder alarm onto the isolated 6A MCB and the smoke alarms onto the lighting circuit.

[ARW]

With all RCBOs then I WOULD share the Smoke, CO detectors and intruder alarm on the same RCBO. It is nice to see someone prepared to install such a good setup.

[Stephen H]

If I do that, if I ever need to work on the lighting circuit, I'd have to kill the power to lighting circuit for safet reasons and by extension risk smoke detector coverage until the lighting power was reinstated?

Also I've seen sheets of legend stickers for labelling ciruits and one of these was the symbol for smoke detectors.

[Stephen H]

and that reminds me, I also need to factor in wiring in a separate kitchen sockets ring main circuit when I refit the kitchen at a later date.

So that's an extra 32A RCBO at the CU.

the kitchen sockets are currently part of the left hand side ring mains.

The idea would be that the existing wiring to the kitchen sockets would be pulled out and used to provide extra sockets in the two bedrooms above the kitchen. The new cables would then be run from the CU to the kitchen sockets and pulled through the plastic conduit from the ceiling downwards.

However, the kitchen refit is a job for a later date and the Dormer bedroom between the CU and the kitchen is likely to be done before the kitchen and laminate flooring is being put down, and the room underneath is being replastered.

So how do I make appropriate provision in a safe manner when replacing the CU for the not yet installed kitchen sockets ring main?

Do I run two lots of T&E from the kitchen RCBO to just an extra socket in the kitchen?. Then at a later date, extend the 1 socket ring main to the rest of the kitchen?

Stephen.

[John Rumm]

Covered here:

[John Rumm]

6 seems a tad low... 16 perhaps?

I would probably aim to start with a few more spare ways... you soon find use for them ;-)