In a Middle eastern location my relative was checking out a potential
fault that occasioanlly tripped the 'whole house' GFCI/circuit breaker
of his living accomodation.

Poorly built 'villas'; often by semi-skilled cheap labour. No fault of
theirs because workers are imported, low paid, untrained and with
little no proper training or equipment and then sent back when work is
finished. Also those temporaraily imported workers have no hope
whatever of ever building a future in a new location or being accepted
as permanent citizens; their purpose being to earn enough to send back
some sort of living to their families in their countries of origin.

There a UK style 230 volt system; two wire (plus ground/earth) with
one wire being live at 230 volts and the other neutral (not the North
American 115 - 0-115 system) is used.

What my relastive found was the cause of the problem was that at least
one of the neutrals in his living unit was someehow shared with
something in the next living unit and under certain conditions
unbalance could trip 'his' protective equivalent of a whole house
GFCI!

Being a technical person he was able to figureit out; although not
sure if he was able to cure it.

BTW there was real 3 phase (3 phases at 230 volts to a common neutral
coming in to that 'villa' the size of a typical 3 bed, 2.5 bathroom
'town house' with a total of 8 largish 230 volt Air Conditioners on
the two flooors!