Can mcb sensitivity be adjusted?

[abenn]

About a year ago I had my old fuse box replaced with a modern distribution box (is that the right term?) which uses an mcb on each circuit.

Ever since then, whenever two particular light bulbs blow they always trip the lighting circuit mcb. The two bulbs in question are mounted horizontally in almost-flush ceiling mountings, and they're the only ones that trip the breaker when they blow. Since they never used to blow the fuses in the old box I'm presuming that this is happening because the mcbs are so much more sensitive than 5A fuse-wire.

The bulbs in question are traditional tungsten filament bulbs: I tried replacing one with an energy-saving bulb, but it blew after one hour of use -- seemingly overheated by the horizontal mounting and the relatively poor airflow.

So, is there any (safe) way I can reduce the sensitivity of the relevant mcb?

 

[baz1968]

Some good info here

//www.diynot.com/forums/viewtopic.php?t=117103&sid=17492229f5ec67cc6e46bcc1ffc53693

 

[Steve]

Energy saving lamps dont overheat by being placed at odd angles or in confined spaces. Chances are you had a duff lamp. They dont get very hot at all, TBH - Touch one while its on, most are fairly cool running, this is why they are cheaper to run, because more energy is turned into light instead of heat!

You can get less sensitive MCBs, these are known as C type. But to do this safely an electrician must first confirm the circuit is suitable for them.

 

[Adam_151]

Try a better make of lamp, the better makes, Osram etc contain internal fuses that are more likely to discriminate with a BSEN60898 type B 6A MCB

The cheaper makes of lamps have a fuse that doesn't always discriminate properly, and if you get really unlucky and get ones that are knocked off in a small concern in a developing nation, they might not have any fusing at all (which can lead to them exploding upon failure!)

 

[abenn]

Thanks for the replies. Sounds like my first port of call is to try another energy-saving bulb -- the one that blew after an hour was surprisingly hot so, as Steve says, maybe it was a dud.

Then, if that fails, I'll try a major brand of incandescent. The ones I normally use (or used to use, 'cause I've gone energy-saving everywhere but these two problem lights) are Sainsbury's own brand. But they've never given me any problems in normal vertical fitting.

Don't worry, I won't be fiddling with the mcb myself. If I need to explore whether a type C is suitable, I'll be getting an electrician in

 

[abenn]

Well, I've had a new energy-saving bulb in the problem light for several weeks now. So the first one must have been a dud.

I'll find out in a couple of years' time (hopefully longer) whether or not it's going to trip the breaker when it eventually dies. Until then, no change to the MCBs

Thankyou for the support and advice.

 

[TicklyT]

If you only replaced one lamp out of two in a fitting, the energy-saving lamp might have been 'cooked' by the heat from the tungsten filament lamp
The energy saving lamps save energy by radiating most of their output as light, whereas tungsten filaments radiate more heat than light. The components of the energy saving light probably can't cope with the temperature tungsten lamps run at.

 

[mikely]

The energy saving lamps save energy by radiating most of their output as light, whereas tungsten filaments radiate more heat than light.

A CFL only converts about 8% of its electrical input into light so most of its output is still heat although a lot less than the equivalent incadescent. In some situations, energy saving lamps will not cope with the heat that they produce themselves. CFLs require electronics to make them work which, in an integrated CFL, are built into the base of the lamp. The reliability of the electronic components drops dramatically as temperature rises. Unlike a conventional incadescent light bulb that is quite happy operating at high temperatures, if you use a CFL in an enclosed or poorly ventilated luminaire, it will overheat and fail much sooner than the quoted life.