Now many hotels use room cards for electricity. Only when the room card is inserted into the slot can the electrical appliances inside be used. The room card is equivalent to _ _ _ _ in the circuit.

(1) The room card can control the work of electrical appliances, and all the electrical appliances in the room will not work unless they are inserted into the slot, so the room card is equivalent to the main switch (switch) on the home circuit trunk line;

(2) The working conditions of the electrical appliances in the room do not affect each other, so the electrical appliances are connected in parallel, and their normal working voltage is 220 V. 。

So, the answer is: master switch; ? And; 220.