Quadnet Control Panel Engineering and Commissioning Manual
52
Eg, if the resistance reading at Loop end 1 were 9 ohm, and at Loop end 2 were 3 ohm then it may
be estimated that the short circuit lay approximately 9/(3+9) = ¾ of the way round the addressable
device circuit from Loop end 1. Investigating that area, and introducing a split to the Loop –ve as
required, will allow it to be tracked and rectified.
Loop +ve to Earth
If the fault is a
short circuit from screen to loop +ve
then it will only be identified with an
electronic test meter at that individual length of cable due to the inbuilt short circuit isolators in each
device.
To locate this manner of fault, split the +ve core of the loop at approximately a half way point on the
loop, then reinitialise with only Loop End 1 connected to the control panel.
Even though the initialisation will fail due to the enforced open circuit, the earth fault will only be
indicated if it is located within the section of the cable which was initialised. The split may then be
reinstated in another position and the process continued, until the section of the system suspected
of containing the earth fault is small enough to allow each portion of cable to be individually tested
with an electronic test meter.
