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Lenny Jacobs

On 13/07/2017 03:57, wrote:
On Wed, 12 Jul 2017 10:23:24 +0630, Lenny Jacobs
wrote:

On 12/07/2017 08:54, wrote:

My "suspicion" is any one , or possibly combination of 2, would cause
the problem. Still don't know exactly what amperage the branch
breakers are, but he has a 63 amp "sub-main" that trips. If he has 7.5
amp breakers (equivalent to 15 amp 120 volt) and he has 25 running an
average of 1/4 capacity, that is 46.875 amps. Say the other 4 are at 6
amps each, the main may trip,(70 amps) while shutting any 1 off may
keep it from tripping at 64. The "short" resistance in the 4 may not
be exactly the same - one may draw heavier than the other on a given
day (it IS a "random" fault) - so shutting all 4 off, then turning the
others on, it may be different combinations that work from day to day.

Well, I have about 10 lights, one water heater (about 30 gallon), one
ceiling fan, three refrigerators. When I turned on TV/DVD, used a
kettle, turned on A/C, used the range in the kitchen, the breaker was
not tripped. It would take a lot more than these to overload a 63A breaker.
You have NO IDEA what amperage the other 4 (that cause the trip) are
drawing. What is the rating of the branch circuit breakers? The water
heater is likely 30 amps, the range is likely 40 amps (if it's all
turned on). That is already more than 63 amps!!! If the range is off,
it draws nothing, of course - but you do not indicate if it is in use.
The fridges could be drawing 3.5 amps each - perhaps 7 when starting,
and about the same when running the auto defrost cycle. When it kicked
the kettle wa not in use? Or the AC? Were the lights on? With
everything else turned off, can you turn on the 4 "bad" breakers
without tripping the main?

If I turn on the bad breakers, the sub-main GFCI breaker will be
tripped. Maybe not be immediately. Maybe in one or two days. To save the
trouble, I just leave them off.