Exploding bulbs

[egg661]

Hi all
we have a couple of table lamps. differant makes and used in different places that are pluged into the plug sockets.
They are 3 amp fused.
randomly the bulbs will explode when turning the lamps on the last one lasted 6 months.
The fuse board is cartridge fused and it is a TT supply.
Do you think I have a problem on the ring or maybe a supply power surge occasionally?
I do not have any problems using the other sockets on the ring or these ones with other applicences
Regards Mark

 

[ericmark]

When a bulb blows it can cause ionisation which will allow large currents to flow. As a result they should have an inbuilt fuse. however some cheap imports Ikea for example don't have these built in fuses so the bulb blows with a bang. And although the regulations say there should be a glass to prevent bits escaping when for example a quartz halogen lamp blows it is expected that all manufactures obey the rules. So where there should be an inbuilt fuse no protective glass is fitted.

 

[egg661]

The bulbs are tungsten candle bulbs. I dont think they are cheap bulbs.
They were purchased from a major diy shop?

 

[Taylortwocities]

I dont think they are cheap bulbs.
They were purchased from a major diy shop?

 

[Space cat]

I've never had a TT supply (and I'd prefer to keep it that way) so I can only speculate. Just looking at the physics, you have two single wires, quite widely spaced, delivering the power to your house. That's a setup with a lot more inductance in it than the more common underground cable where capacitance dominates.

When a bulb filament blows it causes a heavy burst of current followed by a very abrupt drop. (In my experience, when a bulb blows it nearly always takes out a 3 amp plug fuse or a 6 amp CU breaker. ) Inductive circuits don't like rapid changes in current. When the metal vapour that was once a filament does try to break the current, an inductive supply will respond with a voltage spike in an attempt to keep the current flowing. Put another way, the energy stored in the magnetic field around the overhead wires gets dumped in the path of least resistance - which is the metal vapour in the bulb. The result might just cause a bulb to explode.

But, like I said, that's pure speculation on my part.

 

[securespark]

When you say "energy bulbs" do you by any chance mean "low-energy lamps"? Or CFL's, as they are known in the trade.

 

[bernardgreen]

Put another way, the energy stored in the magnetic field around the overhead wires gets dumped in the path of least resistance - which is the metal vapour in the bulb.

An accurate speculation. The energy does gets dumped in all available routes from toaster to lamps with more of the share going through the lower impedances. Howver the energy stored in the inductance of the supply system is so small as to be insignificant in the destruction on a lamp.

When a lamp is operating normally only the filament is heating and the filament support wires are not contributing to the heating. When the filament fails a plasma type discharge can occur and at this point the support wires become the electrodes for the extremely high current through the plasma. If there is no fuse to rapidly stop the current then it is possible that the support wires could be vapourised by the plasma. That increase in metallic vapour could raise the pressure inside the lamp to the point at which it explodes.