We always carried 2 way B22 adapters with out public address kit [which all had 2 pin 5A plugs] and commonly connected to a lamp for our power. The thoughts of non earthed microphones etc gives me the heeby geebies now. Someone deciding to turn lights off for a 'slow dance resulted in losing the music on more than one ocassion.
I remember the bathroom heaters which plugged into a B22 and a 4 position pull switch for light, 1KW heater, both, off.
I'd imagine the current limiting factor will be the spring or spring tension.