On Sat, 15 Jul 2017 08:20:53 +0630, Lenny Jacobs
wrote:

On 13/07/2017 23:27, wrote:
On Thu, 13 Jul 2017 11:28:13 +0630, Lenny Jacobs
wrote:

On 13/07/2017 09:33, wrote:
On Thu, 13 Jul 2017 07:04:53 +0630, Lenny Jacobs
wrote:

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?

Can't tell the rating of most of the breakers. The electrician who
installed them did a great job labeling every one of them. The label
sticker is right on the rating. Judging from the size of the breakers,
they could be 13, 16, or 20 A.


In a euro 240 style system I highly doubt most are over 7.5 amps.
My point of mentioning A/C, range, etc. was that besides those
constantly on appliances, the breaker was not tripped when A/C or range
was turned on. The breaker was tripped when A/C or range was not on. So,
it kind of excludes overloading.

Now it turns out that the tripped sub-main breaker is a GFCI, a wet
circuit is almost certain the cause of the problem.

\Being the sub-mains which are being tripped are GFCI breakers, you
can bet the farm on it. No idea why they have such a ludicrous system
- the branch circuits should be GFCI protected.

I just checked eBay. The price is still around $50 a piece.

Maybe I should replace those four problematic breakers with GFCI, beside
replacing the sub-main breaker.
I'd try just replacing the breakers on the problem circuits first -
they should trip at something like 5ma where the mains trip at 30ma?
fault current.

There are so many wires in the sub panel. How do I find the neutral for
the particular breakers? The breaker boxes in the US have bus to which
all the neutral and ground wires connect to. Not this box. So, where are
the neutral wires? And I heard that three phase circuit shares neutral
wire. That makes things more complex.

Even for the breaker boxes in the US, how to find out which neutral wire
goes with which breaker?


Neutrals are not really tied to a breaker except for that RCCB and
that is all of the neutrals on that feeder. You do need to keep track
of the neutral for each outgoing cable but it is only important when
you are disconnecting it and you want to keep the ungrounded
conductors grouped so you can assure they are on different phases.