Halogen Electric Light Tripping Fuse

[Baxman]

I have just fitted a halogen light in my dining room, this is on the same circuit as my kitchen lights which are also halogens. Total load on the circuit is 500w. When I switch the dining room light on it works but if you switch it off and on it eventually trips the switch in the fuse box (sometimes this happens first time and sometimes it takes a few on/offs). If I reset the switch in the fuse box the light goes on and only trips out again when I switch the light off and then on at the wall.

When I had previous light in the dining room there was no prob with the wall switch - so I am assuming this is all fine.

The dining room light is earthed and I have double checked that the earth contact is good.

Can't understand, any suggestions greatly appreciated.

 

[andy]

dont switch it on and off

 

[Damocles]

Okay. Seems to me this is a surge current problem. You did not say if these are mains or transformer low voltage halogens, but it does not necessarily matter. Some types have worse reputations than others.

When a bulb is switched on, it will draw more current than normal until it gets up to working temperature. This is quite quick, but modern breakers are also designed to be quick to cut off current in the event of a fault current above a predetermined current. Flicking the switch off, then rapidly on again would likely make matters worse, Either the breaker or halogen transformer may not have had time to settle after the first surge.

Or, it may be that breakers are more prone to trip if they have already been verynearly tripped. Anyone know?

Most likely this would not happen if you had a 5A fuse instead of a 6A breaker. Fuses have a small built in delay while their filament heats up. A type C breaker would be more resistant to surges than a type B one (the normal sort).

How many bulbs are on the same switch?

 

[plugwash]

also what brand and type of cu is it (photos helpfull)

this has a major effect on your options

 

[Baxman]

Thanks for the help.

It is a mains voltage unit. When I said switching it on and off, this was with a lengthy delay between swithchings.

In the meantime I have called the manufacturer direct and they have confirmed that the unit can in certain circumstances can cause sensitive MCB's to flip out due to the power surge. He told me that fitting a moderated circuit breaker would fix it. Can anyone advise how to do this?

I assume that i need to identify the type I have, purchase a moderated version of same, switch of the main switch on the fuse board, take the front off the board, remove the old MCB, replace with new.

My main question is, by switching off the main switch on the board does that mean that I can safely replace the MCB or is there power still coming in to the board?

 

[kai]

You should really check your earth loop impedance before attempting to replace a B6 type MCB with a C6 type MCB, the disconnection time of 5 seconds must still be met. Consult a professional electrician.

 

[ban-all-sheds]

You should really check your earth loop impedance before attempting to replace a B6 type MCB with a C6 type MCB, the disconnection time of 5 seconds must still be met. Consult a professional electrician.

Oh FFS.

Kai - to help the non-professional electricians here, will you please post the calculation of how large Zs has to be for a C6 not to disconnect in 5s?

 

[plugwash]

assuming you have to fast trip a C type breaker to get within 5s (i know this applies to type B breakers not sure about type C) then the limit is around 80m of 1.0mm on a C6 on a worst case TN-S

gimme back my old 5A rewirable any day

 

[Damocles]

Or you get a replacement for the mcb containing a cartridge fuse.

 

[Baxman]

Fitted a Type C MCB which did not seem to resolve the problem. Then added a dimmer switch, this seems to have resolved the problem.

Thanks for all the responses

Cheers
Baxman