The Garage circuit was about 12 years old and the hot tub circuit was only weeks old. The two breakers are not in close proximity to each other in the main panel.
They reset both breakers and they have not tripped since [two weeks].
Today the sixty amp double pole breaker that is feeding a recently built master bedroom / bathroom tripped. This breaker feeds from the main panel to a subpanel that houses the breakers for the addition.
The subpanel includes two 20 amp single pole Arc-Fault breakers for the bedroom, two twenty amp single pole breakers that feed directly to two GFCI type outlets in the bathroom and two unassigned breakers.
At the time the 60 amp breaker tripped only the two Arc-Fault breakers were turned on. Neither of the Arc-Fault breakers tripped. Therefore it seems unlikely that an event from the new room caused the 60 amp breaker to trip.
At the time of the trip, the total load on the 60 amp breaker, via the new addition subpanel, was comprised of one digital one analog alarm clock.
Prior to and after the 60 amp breaker tripped the branch circuits served by the new addition subpanel were tested with an Ideal #61-155 circuit analyzer.
This device tests for a host of electrical problems, including: True RMS, voltage drop, line voltage, peak voltage, frequency, ground impedance, hot and neutral impedance, ground-neutral voltage, false and false grounds. Everything tested perfectly.
It also successfully tested the GFCI outlet devices and the Arc- Fault breakers.
This test runs the entire circuit, including the conductors used between the main panel and the new subpanel and the new 60 amp double pole breaker in the main panel that supplies the new subpanel.
Assuming that any trouble in the new addition would have tripped the Arc-Fault breakers, we guessed that the problem must lie somewhere between the new subpanel and the existing main panel. This would reduce the scope of the search to the conductor, the new 60 amp double pole breaker and the main panel.
The conductor is brand new copper UF cable. The Ideal meter test showed no indication of high impedance. An inspection of the main panel showed no indication of a short circuit, arcing or overheating.
When the 60 amp double pole breaker was turned back on it stayed on and was cold to the touch. When checked thirty minutes later with an infrared thermometer, the temperature was normal, as were the rest of the breakers.
It should be noted that the 60 amp circuit that supplies power to the subpanel for the room addition had been turned on over six weeks ago and had operated flawlessly until this afternoon.
Any one of the single pole breakers tripping would just be an anomaly that would not need to be answered unless the problem recurred. But the 60 amp double pole breaker tripping under no load has caused my friends some concern.
Can anyone think of a circumstance that would cause the problems that they experienced?