Flipping switch (by itself) trips breaker
What am I doing wrong here?


You have created a short circuit. When you close the switch, power flows with no load (other than the wires themselves) and the circuit breaker trips to prevent a fire.

You’ll need a double-pole switch (two “line” input connections and two “load” output connections to disconnect this 240V circuit.

Do not re-use the old switch elsewhere. It is likely damaged inside now.