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.
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.
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.
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.
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