Zone Loop Voltage Drop
♦ Zone loop voltage drop might explain why we are having an issue with a sensor on a big school site.
I’ve been trying to check the voltage drop on a PIR putting my voltmeter probes on wiring at a junction box but can’t get any reading. What am I doing wrong? I want to measure that there’s a load without having to open up the PIR and check across the terminals.
A: Testing load on a 12V circuit is fairly straightforward. In your mind’s eye create a circuit that goes from the positive terminal in the alarm panel to a sensor, across the sensor and back to the negative terminal in the panel.
The wire running from the positive terminal of the panel zone to the positive terminal of the sensor is “hot” while the negative wire running from the sensor back to the panel will be at “panel ground potential”.
What this means is that you need to measure the hot wire and the ground potential wire on either side of the sensor – this is the measurement that will show you the load on the circuit.
It sounds like you have both your probes on one side of the sensor – either on the hot side or the ground potential side. No meter with its probes on the same side of an alarm zone will measure a voltage differential.
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