In article ,
"Andy Wade" writes:
"Jethro" wrote in message ...
2) Every time an incandescant bulb blows, the MCB trips
a) is this normal ?
Some people have reported sucesss in preventing such nuisance tripping by
changing the MCB to Type C, and/or uprating the circuit to 10 A. The latter
is only allowed if (a) there are no SES or SBC lampholders on the circuit,
and (b) the as-installed cable ratings are adequate.
Also: make sure that you only use lamps of reputable manufacture which have
internal fuses. I don't know whether it's still the case, but a few years
ago there was a spate of unfused cheap imported lamps on sale. These will
almost always take out the installation fuse or MCB when they go.
I've just investigated an interesting one.
Get a call from my parents -- fridge/freezer is off, and they also
noticed one of the MCB's is tripped off. They're asking me if it's
OK to just switch it back on. I'm rather concerned -- that's a new
ring circuit which I installed only 4 years ago. Racking my brains,
I think it does the fridge/freezer, boiler, washing machine, and
dishwasher -- basically it's the non-RCD protected kitchen appliances.
Somewhat concerned because there's never been a fault in any circuit
I've installed before, I gingerly suggest trying to switch the 32A
MCB back on. It stays on and the fridge/freezer springs back into
life, fortunately before its contents are damaged. Later in the
evening, I get another call -- the oven's off. Ah -- that must be it;
I'd forgotten about the oven on that circuit too. Probably blown its
plug fuse too -- at least it doesn't look like my wiring at fault now!
Yesterday, I pop in to take a look at the oven. Yep, the plug fuse
is dead, but fitting a new one doesn't make the oven work, except
the clock display does come on. Take all the covers off -- it's a
Smeg, and fortunately quite clean inside the casing. First thing I
notice is that everything is live, so I start searching for a broken
neutral. Then I realise the unit has all it's internal switching in
the neutral lines -- how strange? Eventually realise it's the timer
which is keeping everything switched off -- bypassing it makes
everything work, except the oven light (which I only replaced the
week before). After digging out the instructions, I find that the
oven won't work following a power cut until you setup the clock.
Kick myself, put the clock back in the circuit, set it and it's now
all OK. Well, still no clue why the plug fuse and the 32A MCB tripped
but it seems to be working again now.
Finally to the oven light -- buggered if I can unscrew the cover.
Last week when I put it on, I deliberately didn't do it up tight as
they can be a swine next time you change the lamp if grease gets
burnt on them too. Oh well, I have to take the whole lampholder
assembly out, which is quite easy as the thing is still sitting on
the kitchen floor with all the covers off. When I get the assembly
out, (which requires removing the top oven and grill elements), I
can see the glass cover is completely cross threaded. Now I'm sure
I didn't do this last week as it turned very easily. Eventually I
manage to unscrew the glass, and inside the pigmy oven lamp is
completely black, and although the glass is still in place, it is
cracked all over. When I touch it to unscrew it, the glass falls to
pieces, except all the pieces are held together with bits of filament
welded to them. The lead-in wires no longer reach the base of the
glass -- the tip of one of them is welded into the glass at the top
of the lamp. Well, I guess this explains everything now. This lamp
blew, and instigated an arc which blew the 13A plug fuse and the 32A
MCB. I think the blast from the arc blew the glass cover half off,
cross-threading it. I can't explain how the lamp glass was still
inplace, but it wasn't intact, so it may have reformed after the
blast, possibly because the filament somehow managed to weld itself
all over the inside of the glass.
Well, that's a record
AFAIK -- a 15W pigmy oven lamp taking out a
32A MCB. Well done Maplin (supplier of the no-name lamp;-).
It's now got a Philips oven lamp from John Lewis in it.
--
Andrew Gabriel