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Do you install fire alarm systems?

Bit of thread drift going on elsewhere, so I have started a new one.


"Do you install fire alarm systems?" - a question which is asked on insurance renewal, but what does it mean?


IMHO, there is a world of difference between providing a mains supply with third core for linking for a couple of smoke detectors and a heat detector in the kitchen on the one hand (i.e. the minimum grade D2 LD3); and a full on panel with separate detectors and sounder etc. (grade A LD2) in a large house. I consider myself perfectly capable of providing the former, but have never attempted the latter.


So where does the threshold lie? I'd be interested in views on certification too please.
  • "Domestic smoke and heat alarms have mains voltage throughout their circuit. "


    Yes I know that.and concur that any I&T should be confined to that for any other mains-powered circuit.


    "Testing domestic smoke and heat alarms should be carried out following the manufacturers instructions, by pressing the test button. "


    Yes, but is that enough to cover against any claim for liability?


    "The expiry date is on a label."


    Indeed there is.


    So, for a domestic dwelling -  to replace 4 x smokes with same - either optical or ionisation, plus 1 x heat, install to manufacturer's instriuctions and press'test button' to ensure that all sound when any one device is operated.


    What else should be done to mitigate future liability?

    Indeed, what else CAN be done?


    Edit - no idea why pasting results in a hyperlink - sorry.

    Dave Z is correct - the actual boundary seems to become as murky as a lawyer can make it in the event of a mishap - smoke bombs? Thermometers? How far should you have to go for a simple domestic set-up?

  • AJJewsbury:
    1. Broken positive conductor.


    2. Broken negative conductor.


    3. Short between the two above.


    Earth NOT needed in all three cases.

    What about a nail through two cables running together? Shorting one say +ve conductor to the same of another circuit will likely not trip/blow anything but will likely result in mis-operation. 


    Hopefully the fire alarm panel would recognise this as a fault and show such by a fault light and/or buzzer. A case for bright red cables and surface wiring I think to reduce the risk.


    Z.


  • Alan Capon:

    The CPC and screen must be earthed. The detail is in the BS5839 suite of documents, which you need if you are doing this work. 


    Regards,


    Alan. 


    What, even 24 Volt systems have have an earth provided?


    Z.


  • Alan Capon:

    The CPC and screen must be earthed. The detail is in the BS5839 suite of documents, which you need if you are doing this work. 


    Regards,


    Alan. 


    I may consider investing in a set if I can persuade the other half to sell the house.


    Z.


  • davezawadi (David Stone):

    There you are Andy, you can do that, but it needs to be in the limitations box, "Only test buttons pressed". Real fire alarm system tests need smoke, heat, thermometers, etc to check full functionality.


    "Tested in accordance with manufacturers instructions" is the phrase to use for Part 6 systems, which means you pressed the test button. 


  • Hopefully the fire alarm panel would recognise this as a fault and show such by a fault light and/or buzzer.

    But the panel will still need some fundamental means of recognising the fault - if both conductors are normally at the same constant voltage during normal (non-fire) conditions then it's going to be tricky to detect. Likewise open circuits on cables without end-of-line monitoring (traditionally only the sensor circuits had such monitoring, sounder circuits had to have fully protected cables).

       - Andy.
  • AJJewsbury:
    Hopefully the fire alarm panel would recognise this as a fault and show such by a fault light and/or buzzer.

    But the panel will still need some fundamental means of recognising the fault - if both conductors are normally at the same constant voltage during normal (non-fire) conditions then it's going to be tricky to detect. 


    But not impossible. I would expect the panel to detect diverted currents that are abnormal or diverted just like an R.C.D. does. Also the panel will receive healthy confirmatory messages from the detectors that will be disturbed if the separate zone conductors are shorted surely triggering a fault alarm.


    You could always call James Bond fire alarm fault finder.

    Fire Alarm Fault Investigation at a Central London Hotel - Bing video


    Z.


  • But the panel will still need some fundamental means of recognising the fault - if both conductors are normally at the same constant voltage during normal (non-fire) conditions then it's going to be tricky to detect. Likewise open circuits on cables without end-of-line monitoring (traditionally only the sensor circuits had such monitoring, sounder circuits had to have fully protected cables).


    The more modern approaches are considerably more complex and on the 'simple' analogue ones the built in self test is achieved by having the lines reverse biassed to the sounders when not in use, so the internal diodes hold the sounder off, but allows line faults to be detected.

    In a similar way a fire detection is not a short circuit for that would remove power to everything else on the bus but rather a controlled load resistance is added (and even if several call points or heat sensors or whatever are fired together the supply stays up).

    The digital ones have weird burps of square-ish looking  waves riding piggyback on the supply rails to allow the nodes to communicate data. The controller modulates the voltage to address the various sensors, and to reply back the sensors modulate the current they draw.


    At every stage fault detection and built in self test is optimised to try and cover off as many credible failure modes as possible and that has been the approach for at least about 20 years. Around the same time the circuits that measure the internal resistance of the back up batteries to detect plate sulphation were introduced.

    If we did the same level with mains installations then it would take itself off-line and do an insulation and a Zs  test every week and log the results so that the T and M of an  EICR would just be a case of logging into the house debug port.

    M.

  • Zoomup:
    Alan Capon:

    The CPC and screen must be earthed. The detail is in the BS5839 suite of documents, which you need if you are doing this work. 


    Regards,


    Alan. 


    What, even 24 Volt systems have have an earth provided?


    Z.




    That's PELV for you ... where PELV is used ... Now I suppose you could have a PELV TN-C system, but a better performance for EMC can be achieved if the PELV system is TN-S.


    Alternatively, PELV mid-point earthed (DC or AC), and the earth distributed to metallic enclosures to show up faults or for EMC purposes.


  • If you are doing any work on fire alarms for a job you will need specific efficacy insurance for this. As BOD has mentioned above if the alarm does not go off when it should you could have a very large claim against you.


    BS 7671 covers the fixed Wiring to the alarm in addition to the BS 5839 requirements for the supply. The system needs to comply with the relevant parts of BS 5839. The specific requirements needed for the design should come from a Fire Risk assessment and an escape plan carried out by a competent person together with any special requirents from an enforcing authority and the insurance company. You cannot start the design without that information.