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Amended: Jan 2014
“Open circuit” Positive/Negative.
This means after the auto-learn the panel has detected a break in the positive or negative line. The
most likely causes would be:-
Device wired incorrectly. See wiring diagram.
Base switch opening but the detector not making contact. Ensure the base contacts are correctly
screwed down, and none are damaged. Then ensure the detector is replaced correctly.
A negative break may also be caused by a short at a device in the middle of the loop that the loop
device isolators have detected and dealt with. See short circuit middle below.
If the loop voltage drops (below 18 vDC) the devices may reset causing an open circuit negative.
(There must not be more than 2Km of appropriate properly earthed cable used per loop.) If a faulty
device is suspected it can be seen by linking the loop in the panel and disconnecting the far end of
the loop, see diagram.
FIG 54
Measuring the voltage across the end of the loop for correct function this should be over 15V (usually
over 18V). If the panel is left in this state the end devices will go into fault. The faulty device should be
one of the active devices.
