blown bulbs tripping out electrics

[haydar1]

Old fuse box replaced recently and we now have the issue that whenever a light bulb fails the light circuit is tripped out.

The lighting circuit is protected for 6amps on the unprotected rccb. The mains is set at 100mA.

How can we stop the circuit tripping? We're thinking of wearing a torch round our necks just in case.

 

[nstreet]

It's quite normal and if you do a search on the forum you will find various posts on this subject. One as I recall, even as the technical answer as to why this happens.

 

[Qedelec]

How can we stop the circuit tripping?

Don't buy cheap bulbs.

Or you could invest in some CFL's

N.B. CFL = compact flourescent light

 

[Gary0]

Of course, what we need is the technical answer as to how to prevent it when our incandescent bulb does finally blow Seems odd, in this millennium, that the system can't distinguish between situations and prevent it.

There's something about 'nuisance tripping' here.

 

[Qedelec]

Gary
The reason is, that at the point of failure the filament draws a huge current for and instant, the MCB is doing its job. There is nothing to tell it that the overload is only momentary so it trips to protect the cable.

 

[dingbat]

The manufacturer of your consumer unit may supply a cartridge fuse holder to replace the MCB for your lighting (although I haven't seen many of these hybrids lately). It may also be feasible to swap the MCB for a type C or even up-rate it to 10A. You could even consider using, say, a 20A MCB to supply a 5A switch fuse, but all of these suggestions depend to some extent on the characteristics of your installation and would require the services of somebody qualified to assess and carry out the work..

A good idea, if there is space in the CU is to install a nearby light on a separate circuit altogether, so that at least you can see to reset the breaker!

 

[Gary0]

Fair enough Qedelec, but one could get 'slow blow' fuses, but it seems not RCDs ?

Unsure if it's a safety issue they're not available, or a problem packing the necessary control in.

 

[Qedelec]

but one could get 'slow blow' fuses, but it seems not RCDs ?

I think you mean MCB
RCD's wont detect an overload.

Dingbat is right you can aleviate the problem by fitting type C MCB's as these incorporate a time delay but they will also stand 5 to 10 times the rating as opposed to 2.7 to 4 times for type B MCB's so ..... worst case senario:- lighting circuit subjected to 50amps before it trips.... you decide.

 

[ban-all-sheds]

Fair enough Qedelec, but one could get 'slow blow' fuses, but it seems not RCDs ?

In effect that is what Type C and D breakers are.

Unsure if it's a safety issue they're not available, or a problem packing the necessary control in.

It's a safety thing - you need to be much more careful with fault loop impedance values with C's & D's - in fact, D's are wholly inappropriate for domestic use.

You can read more about it here: //www.diynot.com/forums/viewtopic.php?p=76467#76467

 

[Qedelec]

Ban

On the subject of Loop Impedance do you happen to have values of maximum ELI permitted by BS7671 for type 1,2,3, 4 & D.
Not the 80% reduced values in I&T.

 

[Gary0]

Thanks. I seem to be learning a lot recently

 

[ban-all-sheds]

41B2 has got Type D values - guess you'll need an older edition to find Type 1/2/3. Or divide the values in 2D in GN3 by 0.8....

 

[Qedelec]

Thanks Ban, that was what I though.

The tables that list those breakers, such as the the cover of the test forms, all list the 80% value. But the area engineer that assessed me pointed out that the form wants the Max permitted by BS7671.

Considering these are still in use and are not prohibitted it bl**dy daft that you cant find a table listing them.

Like you say I shall have to work them out and put them on a cheat sheet.