Trip characteristics of a type 2 MCB

[John Rumm]

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.

[Andrew Gabriel]

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.

[Andy Wade]

1050 W, but how many VA? I.e. is there enough low-power-factor discharge lighting in there to make the RMS current significantly higher than you're perhaps expecting? Bear in mind that the standard guidance is to assume Ib = 1.8 * power/Uo in the absence of more specific info.

[John Rumm]

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.

[John Rumm]

All incandescent (bar one linear strip light in a utility room - but that is on the other circuit) - lots of quite elaborate multi lamp fittings with candle bulbs in them.

Rather than spread the load between the two circuits they seem to have filled one to capacity and then left the other mostly unloaded. When I have worked out how to get at the wiring I will see if there is scope to rebalance things a bit (or perhaps upgrade the big circuit to 10A (no small lamp fittings fortunately))

[John Rumm]

LOL!

Do I look like dribble?

I found it easier to take the whole bas bar out to cut it, but I guess it could be another Fein multimater application for the brave!

[Andy Burns]

?

[Neil J. Harris]

You have a Wylex NN range consumer unit which takes NB breakers there's lots on eBay but 10A ones are very rare, there are only type 2 ones apart from the 40A size, which is the biggest they did, which is type 1 .

[John Rumm]

The whole CU will be history shortly I expect... so it might be worth eBaying the breakers if they are sought after ;-)