Blowing light bulbs and blowing fuses.

Rolfe

Adult human female
Joined
Sep 11, 2003
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Some time ago, a 60W light bulb in a table lamp in my living room blew. This was not the first time this had happened, but previously I'd just put in a new bulb and everything was fine. This time, no joy. I eventually realised that the 3A fuse in the plug had blown at the same time. I replaced that, and all was well.

Some time after that (we're talking a few months ago, now) the same thing happened again, to the same lamp. Bulb blew, and fuse blew with it.

A couple of weeks ago, the 60W bulb on my bedside lamp blew, and guess what, the 3A fuse in the plug blew at the same time. This lamp was about the same age as the other one and coincidentally from the same shop (M&S). It also had gone through many bulbs in its life, but never blown a fuse before. Both have moulded 3-pin plugs fitted by the manufacturer, and the fuses are changed without dismantling the plug.

I was beginning to feel hunted, but consoled myself with the thought that there might be something peculiar about that particular type of lamp.

Then, on Sunday evening, the 60W bulb in a different table lamp in my living room blew, and you guessed it. I had to replace the fuse as well. This lamp was completely different from the other two, having been made by a specialist blacksmith (ornamental wought iron) and with a 3-pin plug I may actually have fitted myself - the sort where you have to take the back off the thing to change the fuse.

It's difficult to recall back the entire period, but it's possible this has been all the blown bulbs in table lamps (as opposed to fixed ceiling lamps) during the period in question - if another has gone, it was in a lamp with a 2-pin plug without a fuse.

Is there anything odd going on? Is the electrical system of my house trying to tell me something? Should I get it checked by an electrician? Nothing else has happened to make me suspicious of any electrical faults in the house.

By the way, I think the mains supply is 240V AC. The bulbs were all bog-standard things bought in the local supermarket.

Rolfe.
 
It sounds like the average load on that fuse is very near the 3a limit.

Whenever the lightbulbs go, there will be a small surge on the circuit they share, thus the blown fuse..


Take a look at everything you have on that circuit, and see what you can do without or move to another circuit..
 
Not sure about the sharing bit. The fuses that are going are in the plugs of the lamps themselves. And the three lamps are in three completely different places.

Rolfe.
 
A 60W bulb at 240V is only 0.25 amps. But, as Diogenes pointed out, there could be a surge when the bulbs blow. While far from an expert, I know there are different types fuses. We call them here "fast-blow" and "slow-blow". Fast blow fuses blow the instant the current exceeds the rating. Slow-blow fuses can handle transients above the rated current and only blow when the steady current exceeds the rating. Perhaps you need slow-blow fuses?
 
Rolfe said:
Not sure about the sharing bit. The fuses that are going are in the plugs of the lamps themselves. And the three lamps are in three completely different places.

Rolfe.
Oh, that's different.


I go with what patnray said about the slow-blow fuses..

There must be something about the light bulbs blowing, that the fuse sees as a momentary short circuit...
 
...You really need to get circuit breakers over there.

You could be having power dips in your neighborhood. V=IR, R does not change. Everything in your house gets more current momentarily.
 
RussDill said:
...You really need to get circuit breakers over there.

You could be having power dips in your neighborhood. V=IR, R does not change. Everything in your house gets more current momentarily.

Most modern houses have circuit breakers on their distribution boards, but UK electrics also have a fuse in the plug itself. This is what Rolfe is blowing. Although it's not usually recommended I'd have thought you could replace it with a 5a fuse, which should be safe and give you a chance of surviving the bulb blowing.
 
richardm said:
Most modern houses have circuit breakers on their distribution boards, but UK electrics also have a fuse in the plug itself. This is what Rolfe is blowing. Although it's not usually recommended I'd have thought you could replace it with a 5a fuse, which should be safe and give you a chance of surviving the bulb blowing.

If he is truly having brownouts, then the 3A fuse is likely saving a lot of him appliances. If he's just going over current, then ya, pop that 5A sucker in.
 
The thing that seems odd to me is that I've lived in this house since about 1988, and yet until this recent run of fuse-blowing it has never happened before. Did I mention that the scenario is always the classic one - switch on lamp, and bulb goes "pop". Certainly consistent with a momentary surge through the lamp as the bulb goes, but why has it suddenly started happening all the time?

The man in the DIY shop where I went to get some more fuses suggested using 5A instead of 3A too, but that's not really the point. I really want to know if the sudden incidence of fuse-blowing could suggest an underlying electrical problem in the house.

Rolfe.
 
Hey Rolfe,
More about electricity then You wanted to know.
Theres a mnemonic to remember the ratios of Power Volts and Amps.
West VirginiA, W=V*A ( Power is expressed in watts)

Rearrange the formula and A=W/V, in your case 240/60=4A . @ 3A your fuses are a little short.
That in of itself could cause a problem I would use 4-5 Amp slo-blo.
The reason tho for the problem is debatable. Could be bulbs reacting to inrush current ( cold filament draws more then hot). Could be an inductive .load -fridge, heater ,is causing an overvoltage, unlikely tho because the problem occurs when You turn the light on. Has any work been done on the outside lines? Changed power transformer on the pole, new construction? Any new appliances? The pop you hear and the flash you see is the arcing of the two ends of the broken filament which in turn blows the fuse. Check the voltage at the wall sockets. There's also a posibility (remote) that the switches in the lamps are old and arcing when you yurn them on.The bulbs should be rated for lifetime (MTBF) cheapie bulbs will blo quicker then standard or heavy duty. Have You tried an exorcist?
 
TillEulenspiegel said:
Hey Rolfe,
More about electricity then You wanted to know.
Theres a mnemonic to remember the ratios of Power Volts and Amps.
West VirginiA, W=V*A ( Power is expressed in watts)

Rearrange the formula and A=W/V, in your case 240/60=4A . @ 3A your fuses are a little short.

Not to be pedantic, but...

If A=W/V (as it should) then that's A=60/240, or A=.25. You swapped the numbers.

The 3A fuse is 6 times as much as the bulb should be pulling.

One thing I've noticed on several lamps is a tendancy to short inside the socket. I had two in my house go out due to this, and one at my mother's house. It wouldn't explain why 3 went at the same time, but I've noticed it does tend to happen when the lights are being turned on or off, or when they get jostled. The actual sockets are usually cheap little things made from lightweight metal. It's not uncommon for the small copper conductor at the bottem (lead A) to touch the outer conductive sheath (lead B). This is, of course, more likely to happen when the lamp is being moved, twisted, or tilted (and we all tend to tilt a lamp a little when moving those little twist switches or pullstrings). In the case of my mother's lamp, it blew the first new bulb I put in, as well. However, after that it didn't blow another one and worked fine.

It's a stretch of an explanation, but easy to check. Simply unplug one of the lamps in question, take out the bulb, and look for black scorch marks inside the socket. If it did short out in there, you should see a little black splash somewhere around the botttem of the conductive sheath.

Just my 2 cents worth, and probably barking up the wrong tree, but it's easy to check for :)
 
Not to be pedantic, but...

If A=W/V (as it should) then that's A=60/240, or A=.25. You swapped the numbers.

O jeeze brainfart. 1st semester stuff, man are my ears red.
 
I was beginning to feel hunted

Uh huh.

Movie title:

The Lamp From Hell.

Mysterious power outages, a feeling of being hunted: that's always the first warning sign that Something Is Not Right.

And...what should you do, if you want to survive this flick?

A. Flee the house, screaming.
B. Console yourself with the thought that there might be something peculiar about that particular type of lamp.




Uh huh.
 

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