The Siemens 3RB1246-1PM21 is a solid-state overload relay rated 1.25 to 6.3 A at 220-240 VAC 50/60 Hz, with integrated thermistor protection and internal earth-fault detection. It provides 1NO/1NC bistable outputs for overload/thermistor and earth-fault signaling. The solid-state design means no moving contacts to wear out under repeated motor starts — suited for high-cycle applications like conveyors or pumps where a bimetallic relay would fatigue.
Deployment context
The integrated earth-fault detection saves an external core-balance CT and relay — one less device to wire and commission. Bistable outputs hold their state on power loss, so the control system sees the last fault condition even after a brownout.