When The GU10 Lamp Blows

[The_Scotty]

It trips the breaker at the main board.

I have a few rooms that have downlighters in them. Whenever one of the lamps go it trips the breaker thus putting all the other lights out until its reset.

Is this normal occurrence?

 

[GaryMo]

Lighting circuits are normally protected by B type MCB's, either 6A or 10A rated.
A B type MCB will trip instantaneously between 3 and 5 times it's rated current so 18-30A for a 6A and 30-50A for a 10A MCB.

When a lamp goes there's a short burst of increased current which causes the MCB to trip.

An option (won't always work) is to change your B type MCB to a C type.
A C type will trip instantaneously between 5 and 10 times its rated current.
That means 30-60A for a 6A and 50-100A for a 10A MCB.

 

[The_Scotty]

Thanks Gary.

Its not something that bothers me so much as long as there is no underlying problem that is causing the MCB to trip everytime a bulb goes (ie a safety issue)

Its a 10A B Type btw

Out of interest, why would the MCB trip when a GU10 50W lamp goes but not when a standard bayonet bulb in a pendant blows?

 

[securespark]

It depends upon whether the lamps are fused, and if so, whether discrimination has occurred.

 

[The_Scotty]

I aint a scooby what that all means

 

[sparkybird]

It means that better quality GU10 bulbs eg osram, GE etc have an internal fuse in the bulb to stop your mcb tripping. Cheapo ones don't

SB

 

[Steve]

Also depends how the lamp fails.

 

[GaryMo]

Also depends how the lamp fails.

How many different ways can a lamp fail?

Dropping one is exempt

 

[Steve]

Standing on it, dropkicking it . . . . AHEM, but seriously, I heard it depends if you turn it on at a peak or a trough on the AC sine wave.

 

[Softus]

Standing on it, dropkicking it . . . . AHEM, but seriously, I heard it depends if you turn it on at a peak or a trough on the AC sine wave.

I think you mean at the 'zero-crossing' point, as opposed to a point of inflection (peak or peak).

 

[Space cat]

It isn't just halogen lamps that can trip breakers when they fail; ordinary filament bulbs can do it too. I've had this happen quite a few times. Furthermore, the bulbs were on timer switches with built in 3amp fuses - which survived intact!

How many different ways can a lamp fail?

One of the ways in which a filament can fail is that a single hot spot develops. The resistance of tungsten rises with temperature so this hot spot drops more than its fair share of voltage. It gets even hotter, melts and then vapourizes. Now metal vapour is a very good conductor so the current keeps flowing. You have a tiny arc in there. The molten bits on either side of the arc are now under severe strain so they vapourize too and the arc gets bigger. The current is rising as filament is replaced by arc so the race is on. Will the arc blow itself apart before the breaker trips?

Halogen lamps are more likely to trip breakers than regular ones, maybe because their filaments run hotter. Sometimes the arc spreads right along the filament. Have you ever looked at a blown halogen bulb and wondered where the filament went?