BRK 86RAC Smoke Detector Replacement and Additions

I have two BRK 86RAC Ionisation type smoke detector, one in the Hall and the other on the upstairs Landing, these were installed by the builder and in 2008 I added a heat detector (690MBX) in the garage, all three devices are mains powered with battery backup and are interlinked so that they all alert to a detection.

BRK 86RAC Discontinued ionisation smoke detector.

Checking the batteries in the smoke detector I noticed the unit has a life of 10 years from date of manufacture which was 21 June 2002, as the date of noticing this was 4 March 2018, they are well overdue for replacement!

The BRK 86RAC is no longer produced and has been replaced by the  BRK 670MBX.


Checking my local Screwfix had BRK ionisation smoke dectors (part number 81969) for £12.99 and the surface mounting kit (part number 30152) for £2.99, I thought I would add two more to my system, so bought  four of everything.

On opening the boxes, I didn’t realise that the detectors came with 9v PP3 type batteries, so wasted £6.00 buying them, and the other thing was that they are not a direct replacement, the 86RAC base is a smaller size and the plugin connector is a different style.

In the box are the above plus instructions, sticker for the consumer unit and protective detector cover, no fixing screws are supplied.
Fitting –

First job was to isolate the mains supply to the existing detectors which are on their own dedicated circuit, once this was done I twisted the detectors from the base to allow me to take photographs of the wiring.

The existing wiring was Black to Neutral, Brown to Live and Orange striped is the interconnect wire, 670MBX uses Blue for Neutral, Brown to Live and Grey for the interlink, the existing detector had a ferrite bobbin through which all the detector wires passed, whereas the new model doesn’t, I decided to reuse these on the replacement units.


Once the cable colours were recorded, the detector was unpluged and the base completely disconnected to allow the replacement of the new base, once this was screwed into place, the connections were remade.


The wiring in the base looks more complicated than it should due to the change of cable colours, the existing 1mm CSA 3 core and earth used the pre EU harmonisation wire colour convention of Red, Yellow and Blue,  the cable to the new additional detectors which I have installed are in the office and IT cupboard, uses harmonised colours of  Brown, Black and Grey, as the installation has mixed wire colouring, a warning notice to this effect is fixed to the consumer unit.

While the new detector was on the desk, the battery was dated and connected, without a battery installed the detector will not engage in the base, this is a safety feature.

After making the connections, the detector base was fixed to the surface fitting by two supplied screws, the cardboard sealing gasket was then pressed into place covering the detector base fixing holes, the next step was to plug the lead into the base of the detector and lastly twist the detector into the base.


Within the baseplate of the detector is a small plastic extrusion  which can be removed, this is used once the detector is installed as a locking clip preventing the detector being removed from the base with the clip in place.

With all detectors connected and new ones installed, mains power was turned back on, and each detector was then checked that it showed a continuous green LED for power healthy and a flashing red LED every 60 seconds to show the detector is functioning.

The center test button on each detector was pressed and held, this caused the local unit to sound, followed a moment later by all the other interconnected heads.

I had already sealed the cables passing through the ceiling, the final job was to seal the base to the ceiling and paint the exposed part of the ceiling as a result of the base being smaller than the original one.

A point to note was that I was going to use flushed in circular dry lining boxes to make the connections in and hold the base, this would have made the smoke detector sit closer to the ceiling but would of meant a large hole being made, so I decided against it.

Job was very straightforward, adding new detectors was easy as I looped off the landing detector to the other units which were only a few meters away.

8 thoughts on “BRK 86RAC Smoke Detector Replacement and Additions”

  1. Hi

    I need to replace the cover on my smoke alarm can you still buy the covers or do i need to replace the whole thing my alarm is the same one as your first picture

    BRK 86RAC

  2. I have 3 SCO5OOB alarms, installed 4 yrs.ago by professional. The voice alarms go off at 5 am and continue for 3 hours, at 45 minute intervals. The wording (enunciation) is beyond human comprehension! There is no smoke or steam in the vicinity, at this time. What is going on? Batteries installed 2 months ago. Please respond!

  3. Awesome! I wish I had your practical skills. I’m also looking to replace some old BRK86RAC, but yeah, pretty sure I’d burn the house down or something if I tried to replace the whole thing on my own (which would be kinda ironic ;D).

    So, I’m going to bounce around the internet to see if there is anything that can fit the same base plate (hence why I ended up here). If not, I’ll check with my electrician friends. 😉

  4. Hi,

    Thanks for dropping in.

    Changing over to a different BRK model wasn’t too bad, a new baseplate was needed and the footprint was fine meaning not much to touch up, if I was going to replace them all again I would have chosen the Aico range as they have a relay base which was a pain to get hold of using BRK.

    Replacement is a DIY job, the main risks are working off a step ladder and isolating the power and proving its dead, after that its just following instructions, (assuming your not colour blind, as I know this can be a barrier for some).

    Good luck and I hope it all works out.

  5. It is very easy to replace the 86RAC with a newer model. I picked “First Alert BRK SC7010B” because it uses the same power/interconnect connector and it detects both smoke and carbon monoxide. The base ring is a slightly smaller size but it is just a matter of loosen 2 screws to take out the old ring and put the new ring on.

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