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.

--
Cheers,

John.

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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.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

John Rumm wrote:

The new place has two downstairs lighting circuits, the most heavily
loaded of which (about 1050w by my quick count) [...]

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.

--
Andy

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.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Andy Wade wrote:
John Rumm wrote:

The new place has two downstairs lighting circuits, the most heavily
loaded of which (about 1050w by my quick count) [...]

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.

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))
--
Cheers,

John.

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| Internode Ltd - http://www.internode.co.uk |
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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Andy Burns wrote:
On 08/02/2008 18:36, John Rumm wrote:

I had to chop the end off the live bus bar

http://tinyurl.com/2w7k2c ?

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!

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 08/02/2008 18:36, John Rumm wrote:

I had to chop the end off the live bus bar

http://tinyurl.com/2w7k2c ?

In message , John Rumm
writes
Andy Burns wrote:
On 08/02/2008 18:36, John Rumm wrote:

I had to chop the end off the live bus bar
http://tinyurl.com/2w7k2c ?

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!

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 .
--
Neil J. Harris

Neil J. Harris wrote:

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 .

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


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/