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
Yes.
Yes - see FAQ
Exactly (>> 6 A in fact).
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
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.
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.
Pretty common.
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.
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.....
No, we don't ... I am just concious not to have the oven, kettle and shower running at the same time.
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 .....
Yes. Its VERY rare to rip a 60A unit. It took us an office of 70 people all wit PC's...
Yes.
If yes :
Correct.
No sure, but people here know. I just accept it and replace the bulb....and reset the trip.
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
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.
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.
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:
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.
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...
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I'm not sure the maker matters - if the filament supports short it seems to take virtually any MCB, but not most fuses.
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
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