What to do if 30 amp fuse keeps blowing in main breaker box

A 30 amp circuit breaker or fuse is NOT a typical size used for the protection of convenience outlets & general lighting circuits, especially in a residential setting. In fact the National Electrical Code (NEC) prohibits anything larger than a 20 amp breaker to protect a #12 copper wire and and a 15 amp breaker to protect a #14 copper wire. These are the size wires used to supply nearly all outlet and lighting loads in a residence.

It's not clear to me from your question if this 30 amp breaker is a double pole type that is providing power to a second, smaller circuit breaker panel and these outlets are fed from it. This would be in line with what the NEC would allow and what I suspect is the situation. I'm only going to get into this a minimal amount as more information is needed for me to be able talk intelligently about it.

I would shut off the loads that are connected to the 30 amp breaker. If that is a panel, I would shut off all the circuit breakers in it, then turn onn the 30 amp breaker. If it trips, then there is a problem between the 30 amp breaker and the panel. You may have connected line cables to ground or neutral - and vice-versa.

Can you please explain in as much detail as possible what is connected to the 30 amp breaker? Is it a single pole (120 volts) or double pole (240 volts) circuit? What size wires are connect to the breaker terminal(s) What type of cable is connected to it? How many wires are in the cable assembly or pipes? What is the size of wires? If they feeds a second, smaller breaker panel, where do the wires terminate - into lugs on the top or bottom of the panel or terminals of a circuit breaker? What happened or changed to cause this circuit breaker to start tripping? Is this part of a new installation - and if so, was the wiring done by an electrician? Was the work inspected?

Please try to answer as many questions as possible. The more information you can provide will help me get you the best answer.