Some brands of breakers are more sensitive than others and will trip when they near maximum capacity, even if your load does not exceed it. Try to leave some extra wattage available on each circuit so plugging in items like vacuum cleaners or coffee makers will not trip the breaker.
Each circuit breaker in your breaker panel is labeled with the maximum amperage (current) capacity for that circuit. This may differ among circuits, so always check each breaker's capacity individually when calculating the electrical load that will cause that breaker to trip. Standard household circuits in the U.S. are 120 volts, but some circuits have double that capacity for appliances such as stoves and air conditioners. These breakers have 240-volt capacities and will be approximately twice the size of 120-volt breakers. Wattage is the easiest measure of power load to calculate and monitor so you don't accidentally trip your breakers.
Look for the amperage notation on the breaker switch. This will generally be 15 or 20. Also look for the voltage notation, which may be on the breaker switch as well, and will be 120 or 240. If you cannot locate the voltage, assume that breakers that take up one panel slot are 120 volts and breakers that take up two slots are 240 volts.
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Multiply the amps by the volts. In most circuits, this will be 20 x 120 = 2400 or 15 x 120 = 1800. The number resulting from this equation is the maximum wattage load you can place on the circuit before tripping the breaker.
Apply the same calculation to 240-volt circuits. For example, a 240-volt circuit with a 30-amp capacity would allow 7200 watts (30 x 240 = 7200).
Check the wattage for all electrical fixtures and appliances on the circuit. If the total wattage is over your maximum calculation, the breaker will trip.