What is the “a” you are referring to?

“A” is the abbreviation for Amperes (“amps”) which is the unit for measuring electric current. If you multiply Amperes (A) and Volts (V) you get total power which is expressed in Watts (W).

As most domestic appliances use a constant 240V you need to supply more current (A) to keep to get more power. The more current goes through a wire, the hotter it becomes. Fuses and breakers are put into circuits to protect the wiring from having too much current flowing through them. If this protection is not in place, then the wires can get hot enough to cause a fire.