Answer:
Overcurrents
Circuit breakers ("fuses" back in the day) are supposed to trigger when you are requesting past it more power (thus more current, since the tension is fixed and power is the product of voltsge times current). So whoever made that part of the grid did not foresee that many appliances.
Another option could be a short circuit somehwere but I think it is unlikely since the breaker would not trigger only when all three loads are powered on.
