THINGS TO CHECK IF THE CIRCUIT BREAKER TRIPS OFTEN: Weak breakers are pretty common and will need to be replaced. This usually is the result of being overloaded over a long period of time and it becomes weak after it has tripped many times. It may also be caused by a poor contact to the electrical box that the breaker is in or having had a loose wire attached to it. The heat produced by these poor contacts will produce heat that repeatedly trips the breaker and makes it become weak. Too much heat on supply voltage wires that cannot carry that amount of current for long periods of time. A 5 KW electric heat strip pulls approximately 20 amperes of current. So imagine if you have a 60 amp circuit breaker and you have three 5 KW elements and a transformer and a fan motor running off it, you are overloading the circuit breaker. It will work with this load on it for quite a while, but it will eventually start tripping and become more frequent in doing so. You need to either reduce the amount of heat strips or increase the breaker size AND THE WIRE SIZE going to the heater. NEVER increase the breaker size and not enlarge the wire as well. You are in an area of expertise here that will require a real electrician. Please consult him or have an air conditioning service technician and get his recommendation about reducing the heat or rewiring. Hot electrical box that contains the circuit breakers. Consult a real electrician.