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
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
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
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-
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
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