1) - our main fuse (before consumer unit) is 60A. Is this OK in a household
with a 10Kw shower ... no other really big appliances ... 13A rated oven,
kettle ...

2) Every time an incandescant bulb blows, the MCB trips
a) is this normal ? If yes :
i) Why ? (My guess is the resistance of the arc when the filament
pings is c.0 Ohms, which mean I= V/R becomes 6A
b) is there anything I can do ... if the above is true, can you get
"slower" MCBs ?

Thanks in advance

Jethro

"Jethro" wrote in message ...

1) - our main fuse (before consumer unit) is 60A. Is this OK in a
household with a 10Kw shower ... no other really big appliances

Yes.

2) Every time an incandescant bulb blows, the MCB trips
a) is this normal ?

Yes - see FAQ http://www.diyfaq.org.uk/electrical.html#bulbs

i) Why ? (My guess is the resistance of the arc when the
filament pings is c.0 Ohms, which mean I= V/R becomes 6A

Exactly ( 6 A in fact).

b) is there anything I can do ... if the above is true, can you
get "slower" MCBs ?

Yes, there are three 'tripping characteristics, called Types B, C, and D.
These differ in the point at which 'instant' magnetic tripping takes over
from the slower 'thermal overload' trip:

- type B will trip in 0.1 s for 3*In I 5*In
- type C will trip in 0.1 s for 5*In I 10*In
- type D will trip in 0.1 s for 10*In I 20*In

(where In is the rated nominal current).

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.

HTH
--
Andy

1) - our main fuse (before consumer unit) is 60A. Is this OK in a
household
with a 10Kw shower ... no other really big appliances ... 13A rated oven,
kettle ...

Should be OK, provided you don't run all the laundry at the same time and
don't use electric heating of any kind. It is a bit marginal, though. With
an electric shower, a 100A cutout would be nicer.

2) Every time an incandescant bulb blows, the MCB trips
a) is this normal ? If yes :

Yes. As an alternative to the other suggestions, you could fit energy saving
compact fluorescent bulbs. These last ten times as long and don't trip the
MCB when (should that be if?) they blow. They also use about a fifth of the
energy and don't lead to needless pollution of the atmosphere with carbon
dioxide causing global warming.

Christian.

2) Every time an incandescant bulb blows, the MCB trips
a) is this normal ? If yes :

Pretty common.

i) Why ? (My guess is the resistance of the arc when the filament
pings is c.0 Ohms, which mean I= V/R becomes 6A

Yes - the arc starts at the break, then burns back along the filament to the supports, causing a
high current flow until either the MCB or the bulb's internal fuse trips.

b) is there anything I can do ... if the above is true, can you get
"slower" MCBs ?

You can get MCBs rated for motor loads - MCBs come in A,B and C ratings, not sure of the exact
differences - I tried to buy the proper one for a fixed aircon, but the bloke in the electrical
specialist gave me a blank look.....

Should be OK, provided you don't run all the laundry at the same time and
don't use electric heating of any kind. It is a bit marginal, though. With
an electric shower, a 100A cutout would be nicer.

No, we don't ... I am just concious not to have the oven, kettle and shower
running at the same time.


2) Every time an incandescant bulb blows, the MCB trips
a) is this normal ? If yes :

Yes. As an alternative to the other suggestions, you could fit energy
saving
compact fluorescent bulbs. These last ten times as long and don't trip the
MCB when (should that be if?) they blow. They also use about a fifth of
the
energy and don't lead to needless pollution of the atmosphere with carbon
dioxide causing global warming.

We have energy-savers where we can ... but what prompted the query was a
100W bulb which is switched from one of these security-timer type panels
that replaces the main switch. It will only work with incandescant bulbs ...
I had visions of the bulb blowing the lighting MCB while we're on holiday
......

Jethro wrote:

1) - our main fuse (before consumer unit) is 60A. Is this OK in a household
with a 10Kw shower ... no other really big appliances ... 13A rated oven,
kettle ...


Yes. Its VERY rare to rip a 60A unit. It took us an office of 70 people
all wit PC's...

2) Every time an incandescant bulb blows, the MCB trips
a) is this normal ?

Yes.

If yes :
i) Why ? (My guess is the resistance of the arc when the filament
pings is c.0 Ohms, which mean I= V/R becomes 6A

Correct.

b) is there anything I can do ... if the above is true, can you get
"slower" MCBs ?


No sure, but people here know. I just accept it and replace the
bulb....and reset the trip.

Thanks in advance

Jethro

We have energy-savers where we can ... but what prompted the query was a
100W bulb which is switched from one of these security-timer type panels
that replaces the main switch. It will only work with incandescant bulbs
....

You could fit a relay to it to allow energy saving bulbs to be used. The
presence or absence of the relay is often the difference between automatic
switches that can and can't support energy saving bulbs.

Christian.

" and don't trip the MCB when (should that be if?) they blow."

I beg to differ - I`ve only had one go in about 5 years of using them
throughout but it went with much evil smelliness, taking the entire circuit
(fused) down with it.

Will



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I beg to differ - I`ve only had one go in about 5 years of using them
throughout but it went with much evil smelliness, taking the entire
circuit
(fused) down with it.

Fair enough! I've only had one or two go in five years and they've just
stopped working.

I had one that didn't blow that, due to some poor sealant on a shower screen
on the floor above, had most of the shower water going *through* it. By that
I mean inside the glass envelope. It didn't even get dimmer!

Christian.

Christian McArdle wrote:
I beg to differ - I`ve only had one go in about 5 years of using them
throughout but it went with much evil smelliness, taking the entire
circuit
(fused) down with it.

Fair enough! I've only had one or two go in five years and they've just
stopped working.

I had one that didn't blow that, due to some poor sealant on a shower screen
on the floor above, had most of the shower water going *through* it. By that
I mean inside the glass envelope. It didn't even get dimmer!

The non-electronic ballast ones are pretty much robust for small amounts
of water.
They have large distances between the live and neutral, and all
is pretty much sealed.
Electronic ballast ones OTOH are not quite as robust, as typically any
water will cause leaks between circuitry which makes it explode.

The non-electronic ballast ones are pretty much robust for small amounts
of water.

Yes. Definitely a manual ballast that one. A nasty cheap early one it was.
Must have been almost ten years ago.

Christian.

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

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

Nope, I'm not surprised at all. Only a couple of weeks ago. The 15w pigmy
lamp in the fridge freezer not only tripped the MCB but blow the plug top
fuse and removed about an inch track off the PCB on the control board. What
interested me was the lamp, the glass had gone completely silver. I remember
seeing fuses do it on switch mode PSU doing it but haven't seen a lamp do
it.

Chris...



*** Remove BOGOFF when replying ***

In article ,
Andrew Gabriel wrote:
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.

I'm not sure the maker matters - if the filament supports short it seems
to take virtually any MCB, but not most fuses.

--
*Also too, never, ever use repetitive redundancies *

Dave Plowman London SW
To e-mail, change noise into sound.

A type C breaker should solve your lighting problems. Lights going off
unexpectedly is a safety issue, especially when involving stairs,
kitchens, and so on.

Your 10kW shower eats around 40A, but your 60A supply has really a lot
more capacity than 60A. supplies are protected by wire fuses, and you
have to go way above 60A to pop the fuse. So no problems expected
there. You could probably put a 100A load on it and never see it blow.
Not recommended, but perfectly possible.


I've seen flats run on, I'm trying to remember, but it was one (round
pin) mains plug per flat, so either 15A or 5A per flat. Probably 15A.
Tenants considered it a pita but lived with it - just a case of
picking low power appliances, and unplugging things when you want to
boil the kettle, cook, etc etc.

Oh yes, I remember the fitted ovens too: 1950s things with no
thermostat - absolutely hopeless to cook on. You have to sit and watch
the temp dial, and switch them on and off to regulate the temp. And
on, off, on, off... Ridiculous.

It was in the late 90s I saw this too!


Regards, NT