Andrew Gabriel wrote:
In article ,
John Rumm writes:
Does anyone have a set of trip curves for an older type II MCB they
could point me at?

I was under the impression that they were not that dissimilar to modern
type B devices, but was getting somewhat different behavior from what I
assume is just a faulty device.

The new place has two downstairs lighting circuits, the most heavily
loaded of which (about 1050w by my quick count) was thermal tripping
after a few mins with a decent proportion of the lights on.
Investigations showed even a load a little below its rating would cause
a trip.

The thermal tripping is the same. Actually, careful reading of
the curves in an old wiring regs would imply Type 2 is fractionally
more tolerant of overload, but that's probably reading the curves
more accurately than they were plotted.

Temperature has quite an effect. If the breaker is getting warm
or hot, the thermal trip current will drop.

Sounds like a knackered device as I suspected then... it was definitely
less tolerant in the thermal part of the curve than I would have expected.

I have replaced it with a 6A type B that I had to hand. This will do
until I replace the CU (currently 10 way with all ways on one master
30mA RCD including outdoor circuits). Alas it is a 20 ish year old wylex
jobbie with a "sort of" DIN rail mounting - with no bottom part to the
rail and an extra top ridge that the MCBs clip under. I had to chop the
end off the live bus bar to get the new MCB in, and then wire across to
its input from the input of the adjacent MCB.


--
Cheers,

John.

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