Not an issue for newly built apartments, perhaps, but I've been living in an old one for the past year and the electricity is just really poorly done. I've had the circuit breaker fail on me while doing laundry (1kw) and warming up some pancakes in the microwave (1kw). And that's without my neighbour being home, as (go figure) we're on the same circuit breaker.
>>IkmoIk+(OP)
Do you pay for his use or does he pay for yours? Or is the circuit breaker somehow before the mains panel? (Which I find hard to imagine, but then again your situation is already quite strange.)