Replacing a wired smoke alarm

[sophiejazz]

The 2 wired smoke alarms in our house are 10 years old.
The previous tenant had tampered with them so to be on the safe side I'm replacing them.
The alarms are Deta and the model has been discontinued.
Will I be able to replace them with any new wired alarm? (The wires are in a 'plug' behind the casing screwed to the ceiling)
Also, surprisingly, the date next to MFG is 05.12.15, I'm sure this must be a mistake as that is more likely to be the date that it should be replaced.
Many thanks

 

[SFK]

Regarding the Date, it is likely to be reversed to keep it secret from customers and sometime to make it easier for computers to keep filenames in chronioloical order.
If they have done this then date says 2005/Dec/15.

You can normally replace the wire smoke alarms with any new ones.
All wired smoke alarms normally require four wire connections: Earth, Live, Neutral and Signal (the first alarm to sound, uses this signal wire to tell all the other alarms to sound).

There is a simple wire diagram here http://www.aico.co.uk/How-do-I-wire-hard-wired.html <<< this is not a promotion of these alarms, simply the first I found on Google.
Note that the smoke alarms are connected with Three core plus Earth Wire. And many use the colours differently. So before you take down the old alarms make a note of how the cables are connected and their colour.

Regards SFK

 

[sophiejazz]

Many thanks, this was so helpful.

 

[stillp]

Regarding the Date, it is likely to be reversed to keep it secret from customers and sometime to make it easier for computers to keep filenames in chronioloical order.

Year/Month/Day is the ISO sequence for dates - most significant first, least significant last.

 

[SFK]

You mentioned plug leads on your old Deta smoke alarm.
To save you time and effort may I suggest that you see if your Deta are they the same as the BRK smoke alarm at Screwfix?
If you follow this link and click on Specification, you can download a manual and see if they look the similar before buying. Also, do NOT get the one without the backup battery. Make sure it is one of the ones with a backup battery.
http://www.screwfix.com/p/brk-670mbx-679-dicon-ionisation-alarm-with-9v-battery-backup/81969?kpid=81969&cm_mmc=Google-_-Product Listing Ads-_-Sales Tracking-_-sales tracking url&gclid=CjwKEAjwwOvABRC08aedoZ_lnTMSJACs_cbuPyBEZ39C0h5x6mMZz2flL7ToWsL8lanCMDeCG_b4ZhoCzV_w_wcB

Sfk

 

[sophiejazz]

You mentioned plug leads on your old Deta smoke alarm.
To save you time and effort may I suggest that you see if your Deta are they the same as the BRK smoke alarm at Screwfix?
If you follow this link and click on Specification, you can download a manual and see if they look the similar before buying. Also, do NOT get the one without the backup battery. Make sure it is one of the ones with a backup battery.
http://www.screwfix.com/p/brk-670mbx-679-dicon-ionisation-alarm-with-9v-battery-backup/81969?kpid=81969&cm_mmc=Google-_-Product Listing Ads-_-Sales Tracking-_-sales tracking url&gclid=CjwKEAjwwOvABRC08aedoZ_lnTMSJACs_cbuPyBEZ39C0h5x6mMZz2flL7ToWsL8lanCMDeCG_b4ZhoCzV_w_wcB

Sfk

Many thanks,we did get the BRKs, had an electrician fit them. Whilst when the alarm on the ground floor goes off it triggers the first floor; the first floor alarm when set off doesn't trigger the ground floor. We got on to BRK tec services, hadn't experienced this problem before but suggested swapping the alarms round to establish whether it was the alarm or the wiring, as yet we haven't tested that out. they both work and that's the main thing. My own theory is the electrician perhaps hasn't done something quite right. (It did say on the box don't test with fire and he did.)

 

[SFK]

Uhm strange. The way these work is relatively simple. When smoke alarm 1 goes off, it makes the Signal Wire go from 0Volts to some higher voltage. All the other alarms connected the signal wire then sound when the Signal Wire goes from 0Volts to some higher voltage.
So if: "Alarm 1 is able to signal to Alarm 2 to start its alarm, but Alarm 2 is unable to signal to Alarm 1 to start its alarm" then this suggests that it is (probably) wired in correctly as it shows that there is a wired signal connection between the alarms.

So my guess is that ether:
- Alarm 1 is broken in that it is unable to detect when the the Signal Wire goes high when Alarm 2 is sounding because it has detected smoke.
- Alarm 2 is broken in that when Alarm 2 detects smoke it is unable to Change the Signal wire from OVolts to a Higher voltage and so Alarm 1 does not sound.
- (and least likely) there is a poor connection at a junction on the Signal wire (ie the wire not screwed in properly), resulting in a high resistance reducing the voltage, resulting in the Signal Wire not always getting to a high enough voltage to sound one of the Alarms, but high enough to sound the other alarm.

I feel that swaping alarms over would make little difference, but worth a try as might address my 'poor connection' suggestion. So would also recommend getting two (not one) new alarms and putting these in place and getting money back on other two as defective.
sfk

 

[SFK]

Also, There is no need for a 'real' smoke test. The smoke will not damage it, but the heat from the flames can (and can burn your carpet/house when I have seen them tested with lit news paper).

Normally press and hold the test button, the alarm you are pressing will then sound after about 1 second, and then about 2 or 3 seconds later (when it sends a signal down the Signal Wire) all the other alarms will sound.
Do this for all (or in you case both) the alarms in the house once a year.

 

[sophiejazz]

Also, There is no need for a 'real' smoke test. The smoke will not damage it, but the heat from the flames can (and can burn your carpet/house) when I have seen them tested with lit news paper).

Normally press and hold the test button, the alarm you are pressing will then after about 1 second sound, and then about 2 or 3 seconds later (when a signal is sent down the Signal Wire) all the other alarms will sound.
Do this for all (or in you case both) the alarms in the house once a year.

Yes, he did singe the brand new carpet!! I suspect he held the paper close to the alarm and the burning bits of paper fluttered down, I was down stairs and only discovered the marks on the carpet after he left. There really was no need for the real flame test as the hold test button worked. He is a retired electrician, a nice guy, but I wont be using him again.