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Section 2: Wiring Problems - RTU Doesn't Detect Alarms

Previous Page: Section 1: RTU Doesn't Report Alarms
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  1. Make sure the alarm doesn't have a qualification time.
  2. When you're troubleshooting wiring, the first question to ask is "Is the wiring new or old?"
  3. If the wiring is new, check for pinched wires, broken wires, bad soldering and pinout errors.
  4. If the wiring is old and it was working OK before, check if anything has changed. Have cables been moved? Has there been bad weather? A lightning strike could have zapped a component. Check for broken wires. Check the connectors and see if they're loose or corroded.
  5. Test the wiring: Take the sheathing off the cable and test it with a voltmeter. You should see approximately the same voltage as the voltage powering the RTU.

What's going on: Most RTU alarm connections are contact closure to ground. (But see Step 9 of this section for an exception.) If an alarm point is not sending an alarm, the potential voltage in the wire is approximately the same as the RTU's power voltage, or possibly 1 to 1.5 volts less.

  1. Trigger an alarm, and the voltage on the wire should go to zero. If it doesn't you most likely have a nicked wire or a broken sensor.
  2. Check the continuity of the wire by shorting both ends. (Connect a voltmeter at one end of the cable and short the other end; your voltmeter should show approximately zero ohms.)
  3. You might also have a problem where the sensor is sending a ground, but the potential voltage stays on the line. Test this by connecting a wire between the RTU's ground pin and the pin powering the alarm. If the RTU then shows an alarm, the wire is defective.
  4. If the wire is OK, but the RTU doesn't sense an alarm, check to see if the alarm connection is actually a contact closure to battery. This kind of closure will have the same voltage as the potential voltage on the wire, so no current will flow.
Next Page: Section 3: RTU Sends False or Fluctuating Alarms
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