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In class A wiring, 2 wires start from alarm control panel terminal, run through fire sensors / detectors and the same 2 wires run back into the alarm control panel and get connected as 2 more wires thus there would be 4 wires at the panel totally. This would help the control panel monitor all the sensors / detectors even if a loop wire breaks in the middle.

In Class B wiring, the control panel is just connected to 2 wires. These 2 wires run through fire sensors / detectors and terminate at end of line resistor. Thus if any wire breaks in between the sensors that are connected to control panel end of wire would only be monitored. The broken wire side of sensors won't be monitored

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โˆ™ 2009-08-26 05:25:59
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Q: What is the difference between 'Class A' fire alarm vs 'Class B' fire alarm wiring?
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