An electric switch is disclosed, in particular an electric circuit breaker. In at least one example embodiment, the switch includes a measuring channel for measuring an electric measured variable and is switched off when the result of a measurement reaches or exceeds a limit value. To test the mode of operation of the measuring channel, the electric measured variable is switched to a reference channel and a reference signal source is switched to the measuring channel and the reference result obtained via the measuring channel is compared with a reference setpoint. The switch is also tripped if, to test the mode of operation of the measuring channel, the electric measured variable is switched to the reference channel and the result obtained via the reference channel reaches or exceeds the limit value.