Strange Electrical Problem

> Can anyone think of a circumstance that would cause the problems that
>they experienced?
> TIA

>> Can anyone think of a circumstance that would cause the problems that
>>they experienced?
>> TIA

>I know exactly why, somethings fucked up and they need to get the
>contractor back out there before the house burns down.

> When one of our neighbors came back from vacation they found that the
> 20 amp single pole breaker for their hot tub and the 20 amp single
> pole breaker for their refrigerator in their detached garage had
> tripped. Neither GFCI type outlet served by these breakers had
> tripped.
> 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?
> TIA