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1010/2020 INSTALLATION AND PROGRAMMING MANUAL PAGE 15

COMMON FAULT FINDING TECHNIQUES

If using optional shielded twisted pair cable to minimise radiated emissions of radio

frequency energy, do not allow the shield drain wire to enter the cabinet. Connect the drain wire

to the outside of the cabinet via an earth type connector. Maintain the continuity of the shield wire

throughout the loop but do not connect to any devices, and only earth one end.

Before connecting the loop to the LIB-200A or LIB-400 card, carry out the following tests;

1. Check continuity of loop wiring, by placing a short on one end and reading the short with a

multimeter at the other end.

2. Check the loop resistance, same as above (be sure to set the multimeter to ohms), the loop

resistance cannot exceed 50 ohms, which is 25 ohms per leg. (See examples above).

3. Check for devices incorrectly wired, set the multimeter to diode Test, and place the leads on the

cable, the reading should be approx. .645,- reverse the leads- now the reading should be approx.

1.2 or higher, if both readings read low- this indicates a device incorrectly wired, or a short on the

wiring. Note: (Each device has a diode installed)

4. Voltage reading, set the multimeter to D.C. volts and read the voltage at the loop card before

connecting the loop, the reading should be approx. 24 volts, now connect the loop, the reading

should now be 15-16 volts. If the voltage goes down low this could indicate a short on the line, or

there is a device incorrectly wired (possible Reverse polarity), find the device and correct the loop

connections at that device.

5. Earth Fault test, Select ohms on the multimeter and check between each leg of the loop and

earth, if the reading falls below 50,000 ohms, an earth fault will appear on the loop when

connected, find the cause of the earth fault and rectify. (Possible causes of an earth fault are

moisture, inadequate insulation from surrounding building, equipment or materials).

NOTE:

A note on ‘Loop Resistance Measurement’, when ISO-X devices are present. When power is

removed from the Loop, the positive side of the circuit is opened at each ISO-X isolation module.

To measure the Loop resistance, temporarily place a jumper between Terminals 2 and 4 on each

ISO-X while taking measurements. Remember to remove all the jumpers and test all isolator

modules when you have finished taking the readings.

Notifier 1010 User Manual

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