Do you install fire alarm systems?

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.

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.