Class 1, 2, 3 Circuits & Fire Alarm
4:56
That thermostat wire is thin because of how little power is on it.
In this lesson: how Class 1, 2, and 3 circuits are classified by power level (not purpose), why a listed Class 2/3 power supply is what actually qualifies the relaxed wiring rules, mixing-class restrictions, real examples (motor control circuits, paging systems), why fire alarm gets its own article (760), non-power-limited vs power-limited fire alarm circuits, 2-hour survivability cable, and plenum-rated cable requirements.
Based on the 2023 NEC (Articles 725, 760).
