Bulbs Blowing, Breaker Trips

Discussion in 'Electricians' Talk' started by ColG, Feb 14, 2004.

  1. ColG

    ColG New Member

    Is it common when a bulb goes for MCBs to trip?

    Cheers

    Col
     
  2. RES

    RES New Member

    Yes, extremely common. I have been asked about this many times, and the only advice I can offer is to buy better quality bulbs. The own brand supermarket bulbs are more susceptible to tripping out an mcb. There is actually a piece of fuse wire inside the bulb which is designed to 'blow' when the bulb expires. The cheaper bulb's fuse tends to 'blow' a little slower, and your mcb trips first.
     
  3. ColG

    ColG New Member

    Thanks BES
     
  4. Damocles

    Damocles New Member

    Do you have 6A type B mcbs? As far as I can tell this is where the problem occurs. A 6A type B is designed to trip at a lower current than the typical surge from a lightbulb fusing. I reckon its a design fault of this type of circuit. Best practice now seems to be to install 10A lighting circuits,using 1.5mm cable.

    No one on here will give you a straight answer, but I suspect a 6A type C should solve the problem, and still be perfectly safe. However... this depends upon your actual installation.
     
  5. RES

    RES New Member

    Damocles
    Why not fit a 20A breaker with 2.5mm? Or even 32A with 4mm? The sky's the limit.
     
  6. Damocles

    Damocles New Member

    Because it is a good idea to limit the current available in a circuit. That way if someone should connect themselves across the lamp you only get a dead body from the 6/10A, rather than charcoal from the 100A supply running the human arc lamp.
     
  7. Damocles

    Damocles New Member

    oh,and the cables are so much easier to work with. cheaper too.
     
  8. Damocles

    Damocles New Member

    The point of a breaker is to limit the maximum current,but still allow enough for everything to work. The trouble with 6A type B is that it limits current too much.

    Dont have any experience of commercial wiring, but i suspect a house full of fluorescent strip lights would work just fine off a type 6B. Commercially they suggest type C because of switch on surges with fluorescents. In a house lamps would be switched on one by one, so wouldnt normally be a problem for a type B. Wheras a type C is actually needed to make everything work properly using standard bulbs.

    A type B 10A has about the same surge resistance as a type C 6A. i am told, just about enough to survive a bulb pop.

    I reckon this is a bit of a bodge, because of changing from 5A fuses which are more forgiving.
     
  9. The Trician

    The Trician New Member

    As a matter of interest, how about conducting a poll as to which TYPE of lamp causes a type B 6A mcb to trip. Maybe we could narrow down the culprit(s)

    I have never experienced this phenomena in my own house, which has 6 ES spots in the kitchen, and the rest are 'Eneregy-Savers' in conventional pendants.

    So, either I have strayed across the 'right' kind of lighting arrangement or there's not enough fault current getting back to trip the breaker in time...

    Ooh Dear!!
     
  10. RES

    RES New Member

    Trician
    Worst culprits, in my experience, are candle bulbs. Especially if they are horizontal, for example in a wall light.
    I actually found a website/forum, through Ask Jeeves, which was solely dedicated to lamp failure causing nuisance tripping. That's where I got the pointer about internal fuse wire and quality of the bulbs.
     
  11. ColG

    ColG New Member

    Thanks guys, maybe I'll check which MCB I've got and also get some decent lamps.

    Ta

    Col
     
  12. Milton Bradley

    Milton Bradley New Member

    I used to believe that the standard house lighting circuit rating was increased from 5 amp to 6 amps, in the mid 1980's, it was especially to counteract nuisance triping, and now it appears to not be the case.
     
  13. Damocles

    Damocles New Member

    Think the consensus from here is that it needs to be increased to 10A before nuisance tripping disappears. I assumed circuits went from 5 to 6A because the breakers were more sensitive than fuses, so would still break at similar overloads even with slightly higher running load.
     
  14. The Trician

    The Trician New Member

    I thought the reason for changing the current ratings of mcbs etc was because of harmonisation of supply voltages with the EU. 230V instead of 240V? So that a given current for the new lower voltage would have to rise?
     
  15. Damocles

    Damocles New Member

    Na, thats just so you can make exactly the same thing and sell it in 10 different countries. or is it 20 now?
     
  16. The Trician

    The Trician New Member

    Now you're being too cynical - but I love it!!
     
  17. RES

    RES New Member

    What about the new cable colour scheme? That's coming next year isn't it?
     
  18. The Trician

    The Trician New Member

    Yeah! But please save that one for later! See my posts on the colours of tape!
     
  19. supersparky

    supersparky New Member

    just out of intrest we seem to have commercial breaker raiting being tailed by domestic.
    domestic std seemed to be 6mcb back in the day, whereas, commercial seems to always be 10amp, now domestic is starting to have 10amp as std(i do anyway) and commercial has 16amp, moving towards 20amp.....
    so in 20 years time with demend on lighting circuits increasing i suppose we will see the following:

    everyone will have a TP supply
    complete with TP-N bored fitted(can you imagine the size of the 'meter cupbored on the wall!!)
    we will see 60amp in 16mm swa supplying the cooker
    50amp breakers in 10mm t&e for the ring(includind a single core earth to ensure earth continuety when regs finaly see the real problems instead of attempting to cure problems and missing the point completely...if it ever happens)
    100amp shower feed wired in 25mm
    50amp in 10mm supply to shed(comprimising jaccozzi and power shower)
    40amp in 6mm, (with 10mmt&e becoming the std) for lights, with pendantlight fittings the size of your head

    and then we will have the good old 4mm on a 32amp breaker..........for the doorbell!
    of courese there will be a place for 2.5mm........it will become 8coreand earth and alarms will be wired in it...

    and good old 1.5....makes a great dog lead

    and 1mmt&e? whats that then mate? never herd of anything that tiddaly!

    (dont ask about .5 and .75!)
     
  20. Damocles

    Damocles New Member

    yep, thats about right. 100A shower might just give me a real blast.Love that hot water. Whoever said a shower uses less water than a bath?

    But lights is right anyway. Now a 6A circuit isn't enough power for one floor of a house, gets a bit ridiculous having one circuit for each room, what with all those halogens just eating power.


    But but, the issue of nuisance tripping is crazy! Reckon it would be ok if all the lights go out in an airline cockpit if one of the bulbs blows? Thats crazy crazy crazy design. If the only way to fix it is scrap 6A circuits, then thats what should be done officially.
     

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