On my breaker box only one breaker keeps switching off. I reset it and it will stay on again for about 30 minutes then it pops again. No new appliances have been connected to the circuit and I can't figgure out why it is causing just the one breaker to trip.

Possibilites: breaker could be bad, you might have an intermittent short/ground, or loose neutral. An amperage check would be prudent. Circuit breakers have short circuit ratings and inverse time ratings. One can "overload" a circuit and not trip the breaker until it heats up to a certain point before it trips. For instance, a 20 amp breaker will carry 22 or 25 amps perhaps for a short time before it heats up to the point of tripping. This may be the problem, but one can't be sure unless an amperage check is done; with all the electrical equipment running as normal. With a meter one could check for a partial ground/short in the circuit after all equipment is disconnected (unplugged) from the circuit. Electricity can be a really strange critter to troubleshoot. If you can't figure it out, better to see about getting a licensed electrician to look at the problem. :-)