Recently, the service panel circuit breaker for my irrigation pump trips after the pump runs for a few minutes. If I immediately reset it, it trips again, but if I wait a few minutes it will reset and trip after a few minutes. The pump and service panel breaker were replaced 3 years ago with no problems until recently. The pump is 2 HP, 220 volt, draws 15 amps at full load and is thermally protected. When actually running, the pump draws 10 amps when measured with a a clamp-on amp meter. The pump is connected to a fused disconnect box. The 2 fuses in the disconnect box are slow-blow, 15 amp fuses rated for motor start-up loads. The wiring from the disconnect box goes to my service panel and connects to a 2-pole, 20 amp, HACR rated breaker. I have checked all the wiring connections from the pump connection at the fused disconnect to the service panel and they appear fine. The wiring is #12 and runs for approx. 100 ft. underground from the pump disconnect to the service panel. I checked the resistance with a DVOM which indicated 0.9 ohms on the 200 ohm scale. Why would the 20 amp breaker in the service panel trip before the15 amp fuses in the disconnect box blow? Should I just replace the 20 amp service panel breaker, or check further?