Lamps blowing cont...

[davesparks]

Swap them for rough service lamps if they're ES, at least as a temporary measure to see how it goes.

 

[Lucien Nunes]

There was quite a bit of condensation. I was thinking that at times this may cause a short circuit and blow the lamp.

This is a bizarre notion! If you're watering the garden with a hose and someone rips a big hole in it with the mower, would you expect the pressure at the nozzle to increase? The words 'short circuit' indicate that the current 'stops short' of some intended destination, i.e. by definition a short circuit across a lamp prevents current reaching the lamp. By convention a short is taken to mean a low or catastrophically low resistance relative to the rest of the circuit, otherwise we would just call it leakage.

Think about the resistances involved too. Can you really create a short circuit, of low enough resistance to affect the circuit in any way, with condensation alone? You might be surprised to find that if you completely filled the fitting with water, in the absence of an RCD it would at first carry on working. There would be leakage, the water would become loaded with metal ions and its resistance would fall. Eventually it would either trip the MCB or boil itself dry and leave some nasty metallc tracking across the insulation. But it wouldn't for one moment affect the lamp.

 

[HappyHippyDad]

I think it really is time for the 2365 that I keep threatening to take!

 

[Welchyboy1]

If they are external im assuming they are enclosed fittings?, are the lamps the correct wattage?, they usually lower the max wattage for enclosed fittings, may be overheating if they are too high wattage?.?..?

 

[Lucien Nunes]

I don't think it's overheating. Fitting an over-rated lamp tends to overheat and damage the fitting and wiring but not the lamp itself. The fitting might turn into a pool of melted gloop with a 75°C excess temp rise but the effect of this on the lamp filament is negligible because it runs at around 2750°C anyway and almost all its heat is dissipated by radiation, whereas the fitting loses it by convection. Even a glass envelope will withstand a few hundred.

The only filament lamps that are really vulnerable to overheating are high power ones in small envelopes. A traditional non-halogen 1000W projector lamp the size of a cigar needs fan cooling or the glass will melt, although the filament will be OK until it does.

 

[HappyHippyDad]

I just remembered this oldish thread!

Just to update and finish it.. I advised the customer change 2 of the lamps for rough service and 2 for LED's to get a picture of what worked well for their environment. They immediately went out and bought 11 LED's! I went back last week for another job and they said that none had blown since changing.

Thanks to all of you for the advice.