Lamps Blowing !

[spud1]

Does anyone know of other reasons for lamps blowing frequently in a specific mains light fittings other than cheap lamps, vibrations, or overvoltages. Ive come across it several times and dont really ever have a definative answer for my clients

 

[davelerave]

other possible reasons with incandescent

maybe heat build-up or contact problem


overvoltages and surges would prob affect more than 1 fitting

 

[telectrix]

try fitting a rotary dimmer, that way they come on low, less pops.

 

[spud1]

Its just wierd how it seems that multiple lampholders on one fitting can pop so many lamps so frequently and other fittings in same house, with same lamps maybe even identical fitting can be fine ? You can only go on what a client reports to you I know but I have it every so often and it frustrates that I cannot give a definative answer

 

[Newsome3]

ive same problem

ive got to go to a client tomorrow that lamps keep popping!!
i belive that its down to cheap lamps but not 100%

 

[circles]

Well it has to do with connections and contact resistance. A tungsten bulb would last about a month or two in a socket with a high contact resistance. The lights don't flicker or anything but if the contact isn't good between the the socket and the bulb then this kind of scenario exists. The contact is between fairly soft metals, at a microscopic level the surfaces of the contacts are very bumpy and so physical contact between them is only at points of corresponding peaks. The softer the metal then these peaks become squashed and a larger surface area is making contact and more current can flow at that particular point of contact.
Now if you have a weak contact spring in your light socket then the pressure on the contacts is reduced and this flattening of peaks isn't as effective and there becomes a varying of current flowing through contacts.
Alternatively there can also be reduced electrical conductance of old contacts by
by the introduction a thin film or tarnishing whose thickness is a statistical
function of asperity deformation, not enough to create flickering but enough to cause a small unwanted varying of current which can cause the filament of a bulb to give up the ghost a lot earlier than it should. Actually I think this is J A Greenwoods contact resistance equation at work here.
Basically change the socket.

 

[oldtimer]

I looked at a job on Friday and the customer reported that some lamps were not lasting also that her 2 outside pir were not working 1 very old 1 18 months old plus a low voltage track with 12v spots I measured the voltage at 249.4vac at 09:00 and thought this was odd so I called Scottish Power help line who at first agreed as I thought the voltage was too near the tolerance level at 230v + 10% = 253vac. My reasoning was that if it was 249vac at 09:00 then it would rise at night due to the load falling off. So the said get the customer to report it and when she did the "main engineer" said he was not too concerned as they would not come out until the voltage was 264vac ? Anybody else had this ?

 

[spud1]

As i understood it the voltage tolerance for incoming service is as you say +/- 10%. I would have thought that the supply co. has a duty of care to maintain these tolerances so I dont quite know where he has got 264v from ?? Unless they know something we dont. Thanks for your comments everyone, really helpful.

 

[davelerave]

soft-start dimmer would help alright with incandescent(if it's 2-way switched)

i guess a 1-way rotary does much the same job