Troubleshooting Fire Alarm Systems - Look at What the Panel is Looking At

The easiest way of seeing problems in a fire alarm circuit is to use a voltmeter. This is because a problem with resistance or current will also affect voltage. Not only that, in many cases, you don't even have to disconnect anything to measure voltage.

When making the voltage measurements, current and resistance have affected the voltage. If the voltage is higher or lower than expected, current and/or resistance is the culprit.

Example: When the display on the panel says something like TROUBLE NAC 2 (Notification Appliance Circuit Number 2), the voltage on the screw terminals for NAC 2 is wrong.

OK. The Installation Manual doesn't tell you what voltage you should be seeing. To find out the correct voltage, you need to compare voltages.

You know that the panel thinks there isn't no problem with NAC 1, so the voltage you measure on the screw terminals of NAC 1 is the correct voltage. Now you know what the voltage should be on NAC 2.

If the NAC 2 Voltage is higher than the NAC 1 Voltage - There isn't enough current on NAC 2, making the supervision voltage on the circuit higher. Causes of not enough current is a broken wire, a wire loose from a terminal, or possible tarnish on the wire-to-screw terminal connection.

If the NAC 2 Voltage is lower than the NAC 1 Voltage - There's too much current on NAC 2, making the voltage lower. Causes of too much current is an a hard short caused by a pinched cable, too much insulation removed from wires during installation, equipment ripping through cables, or maybe a soft short caused water damage to the NAC circuit, or by a bad horn or strobe.

When there is a NAC x trouble, remember to compare voltages to know what voltage to look for.