A circuit breaker trips when the current traveling through the circuit exceeds the rating of the breaker, causing it to become warm and spring open. This occurs when too many electrical devices are plugged into a single circuit. Moving some of the devices to other circuits should relieve the problem.
Circuit breakers in the home are often rated for 15 or 20 amperes. With 120-volt service, this means they have a limit of 1800 or 2400 watts, respectively. However, circuits should only run at 80 percent capacity for long periods, so if a circuit is loaded near its maximum, it may cause the breaker to trip.