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ZX Fire Alarm Control Panels
16 Supplementary Information
16.1 Locating Earth Faults
•
The control panel continually checks the wiring to determine if any external wiring has become short
circuit to earth.
•
An indication of an earth fault is given by amber LED Indicators on the panel front. The earth point is
normally maintained at 1V above the battery negative terminal. The polarity of the fault will be
indicated with a 'negative' or 'positive' sign on the alphanumeric display.
•
For example:
EARTH FAULT TO -VE ON EXTERNAL WIRING
For service phone
•
The panel will normally continue to work with a single earth fault on the system. The fault, however,
should be rectified as soon as possible.
Locating the Earth fault
•
Most earth faults are found by performing resistance measurements on the cables before connecting
them to the panel.
•
Earth faults can appear on the following external cables:
1.
Sounder circuit wiring
2.
Detector circuit loop wiring
3.
Auxiliary 24V output feed.
•
It is also possible to use a dc voltmeter in conjunction with a working panel to find out which circuit is
shorted to earth. This is particularly useful if the fault is past a loop isolator, as this type of fault can
often not be detected by a resistance check at the end of the loop.
•
The following method describes how to locate this fault by disconnecting the external wiring.
1.
Measure the voltage from the battery negative input to the supply board earth input. On a healthy
system, this will read approximately 1V.
2.
If the voltage is less than 0.3V, the panel will register an earth fault to negative.
3.
If the voltage is more than 1.5V, the panel will register an earth fault to positive.
4.
Each of the external cables can be disconnected in turn while monitoring this voltage. As soon as the
faulty wiring is disconnected, the voltage will return to 1V. This identifies which cable is shorted to
earth.
Please take great care not to disconnect any of the internal board-to-board connections
while the panel is powered up, otherwise damage may be caused to the circuits!
Commissioning Manual
123 4567890
Document No. 996-175-000-1, Revision 01
MORLEY-IAS
Page 55
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