On electrical switches, relays, and circuit boards, the labels L1 and L2 designate line voltage input terminals that connect incoming electrical power from the main power source or circuit breaker. Specifically, L1 represents the primary live hot wire terminal, while L2 represents the secondary live hot wire terminal in 240-volt split-phase residential circuits or multi-pole control switches. Understanding these designations is crucial during electrical installation or component replacement because connecting wires to the wrong terminals can cause equipment failure, trip breakers, or create severe electrical shock hazards. Always verify circuit wiring diagrams and use a multimeter to confirm power status before making physical wire connections to L1 and L2 terminals.
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