OT Electric supply

This is a little OT, but I'm sure someone here will have some input. Since moving house last year I've noticed that we go through an
incredible number of light bulbs. They just seem to be blowing all the time. Granted we have a lot of bulbs (all the light fittings are multi-bulb types), but they just don't seem to last long. When a neighbour commented about the same thing I wondered if the mains supply could be to blame. Could it be slightly over voltage? The next question is how would I check this? I know that the mains voltage is stated as an "average" over a period of time, but is there any simple way I can check this -or does it involve complex measuring equipment.
Regards
Kevin
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On Sat, 29 Jan 2005 10:34:52 +0000, Kevin Steele

Swop to those energy saving ones. They seem to be damped. I have noticed that if you have a 3 bulb light fitting one soon goes, not long after the second goes but the last one lasts ages. replace them as they go and you are always doing it. We swapped outs out about 4 or 5 years ago and we are just starting to have to change them thru old age.
We have recently fitted two 3 bulb spots in the kitchen and these so far have ate 9 bulbs in less than a year but it's hard to get anything bigger in.
Not being an EE it has often made me wonder whether a capacitor across the mains just before the light fitting or one across each holder would stop this surging if that's what it is. -- Regards,
John Stevenson Nottingham, England.
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John Stevenson wrote:

Being an EE, I'd recommend you don't put capacitors straight across the mains. One of my teachers did this to demonstrate caps don't disipate real power (true enough if they're ideal caps, with no internal resistance). The paper & foil innards shot loudly out one end, much to our pleasure.
Short surges can be limited with a surge suppressor. I think the only way to limit a long voltage surge might be a triac circuit to reduce duty cycle as line voltage increases - a simple ac regulator; but it would cost more than, and have the limited life of a normal dimmer switch.
Heat is what kills bulbs early, so if you can't limit power, increase the cooling by mounting them upright or horizontal, dusting the tops & allowing air to circulate by getting a bigger shade.
Guy
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are
there
measuring
Either you are slightly over voltage, or someone locally has a large inductive load sticking spikes on the line. In our case the large inductive load is my workshop !
One other possibility is vibration. Trains whizzing past shaking the building have been know to cause premature failure, as have energetic teenagers in upstairs rooms !
AWEM
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You can check the voltage between live (red or brown wire) and neutral (black or blue wire) with a modern digital meter. The safest place to do this is probably in a junction box - unscrew the top and measure between live and neutral *carefully*. You can kill yourself and burn down the house if you aren't *careful*. If you have any doubts about your ability to do this safely, call in a professional electrician to do it, as an hour of his time is cheaper than a funeral. The indicated voltage should be within plus or minus 5% of 230V. So 218.5V to 241.5V is within acceptable limits. Note that a reading at the top end of that scale indicates that your resistive equipment (bulbs) will dissipate 10% more power than at 230V...
Another possible reason for bulbs to blow frequently is to find that the switch is in the neutral leg of the circuit instead of the live leg. (This is a dangerous situation that needs to be rectified as it means that the bulb holder fitting is 'live' when the switch is off.) As the filament is still energised to 230V when the circuit is open, a cloud of metal ions gets blown off the filament as it cools down, thereby thinning it and reducing its life-span - or so the thinking went when I read that many years ago.
Still another reason for bulbs to blow is when they are turned on and off frequently - do you have young household members who are fascinated by light switches? Mind you, if mine are anything to go by, then they'd be more likely to leave them on all the time, could still lead to failure as the service life expires sooner :-)
Regards
Pete
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On Sat, 29 Jan 2005 11:13:16 +0000, Peter Scales

Just curious - why a 'modern digital' meter? What's wrong with my old AVO8? I know present day meter leads are supposed to be safer, but is there a difference in the reading? & where does 'true RMS' come into things?

I hope our voltage never drops to 218! it's usually around 240, I understood that when we changed to a nominal 230, actual voltages were still to be maintained at about the 240 mark. Or has this been quietly forgotten?

That's a fascinating theory - has it ever been proven to have a significant effect?
I think John is right about the multiple holders leading to a much shorter life.
I just the other day replaced a compact fluorescent which had been in regular use for over 12 years, our house has small windows, so lights are often on in daylight as well as at night - I usually write the date on them when I fit them. One thing which isn't widely publicised is that they (compact fluorescents) will live much longer if you try to always leave them on for at least 20 minutes before switching off.
Cheers Tim
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wrote:

Having a big old Victorian house we have quite a few 3 bulb holders, I forgot to mention that it's these we have changed over to the energy saving 11 and 16w bulbs and that's stopped this incessant blowing. Like Tim some of our lights are on all day and most of the night.
I can't see these two modern fittings in the new kitchen lasting, just went in to make a coffee and another has blown since Thursday and this is all new late spec wiring.
I'd be interested to see anyone else's take on this as I have noticed the three bulb issue for many years, just never read anything about it.
-- Regards,
John Stevenson Nottingham, England.
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On Sat, 29 Jan 2005 11:55:43 +0000, John Stevenson wrote:

Are the bulbs hanging down or pointing up?
I had a 3 light hanging down holder for years which ate more bulbs than I could keep up with. Only by chance did I read the packet in the supermarket which said the 60W bulbs could only be used pointing up. The 40's didn't differentiate, and the current packets in Safeway/Morrisons don't say anything at all about this.
Changing to the 40's about 5 years back dropped the failure rate from 4-6 bulbs a year down to around one.
Not sure why it should make a difference whether the bulbs were pointing up or down - hopefully someone else knows about more on this...
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Duncan Munro
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I was going to write a spiel about convection and tungsten molecules, then thought I'd check my facts. I was unable to find a reference that agreed with what I was going to write, so I didn't, if you see what I mean...
However, I did find some absolutely fascinating sites:
http://tristate.apogee.net/lite/home.asp - have a look at 'Reference Cabinet'
http://www.hstech.org/howto/electric/brian/lamplife.htm - more than you ever wanted to know about blubs...
http://www.seagulllighting.com/DesignerTips.cfm - nice FAQ
I also found lots of references to growing cannabis, for some strange reason.
TTFN
Pete
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John Stevenson writes ....................

There was a thread on this, or a very similar topic, about a couple of years ago. Anybody perhaps have a reference to this?
Mike
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The only reason I mentioned a modern digital meter is because they have a massive input impedance and draw effectively no current from the circuit under test. An AVO8 is probably fine too - it's a lovely instrument. It probably has an input impedance of 20K ohms per volt or something similar and thus probably going to draw next to nothing on the mains. I just know which I'd rather fry - my Maplin special at 2 or my AVO8 at <priceless>.

The power generators will sell you electricity at as low a voltage as they possibly can. The difference in power consumed by your apparatus at 240V as opposed to 230V is over 10% - this is power that has to be generated somewhere... Dropping the voltage to 230V means a saving of 8.2% on power, all other things being equal.

No idea - it's probably a load of bulbs.
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Now that's mighty nice of them... power is sold by the kW h so the higher the voltage the more you use... and pay for.
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Jonathan

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Absolutely correct - but there is a finite limit on installed generating capacity and at times, that limit is reached. The power generators like to have a bit in hand, it saves them all sorts of bother.
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Au contraire - they'll sell you power at as high a voltage as possible. Don't forget that they pay for all power dissipated in the wires between the substation and your house and this costs them less if the volts are high and the current consequently lower.
> The difference in power consumed by your apparatus

This saving is of course a reduction in their sales income since they charge by kWh and not by kAh
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No argument about distribution voltage being as high as possible.

Agreed.
What they don't like is to be caught flat-footed with demand outstripping supply and total available installed generating capacity is a very close match indeed to total demand. In order to keep a little 'headroom' they won't sell every watt they can make, only every watt scheduled to be made. They have to keep a 'spinning reserve' in case there's a sudden unexpected event that causes overall consumption to rise. The alternative is to lower supply voltage and ultimately shed load. The total available power in the system is finite and fixed at any given time and the only parameter that can be varied relatively quickly is voltage (without load shedding). So, they do try to sell all the power they can but what they can't do is sell power they haven't actually got available.
On a cold winter's night, what will happen if a couple of 500MW sets have a boiler tube failure? Will some unlucky souls get their power turned off or will the grid as a whole see a slightly reduced voltage? My money's on the second possibility. In an ideal world, the spinning reserve would take up the slack, but I'm not sure just how much of that is left these days.
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wrote:
| The power generators will sell you electricity at as low a voltage as | they possibly can. The difference in power consumed by your apparatus | at 240V as opposed to 230V is over 10% - this is power that has to be | generated somewhere... Dropping the voltage to 230V means a saving of | 8.2% on power, all other things being equal.
Mains voltage in the UK is now *officially* 230 volts to conform with EU rules, but *actually* 240V because we objected to the change and negotiated a higher tolerance at high voltages than low.
http://www.gbaudio.co.uk/data/mains.htm

achieve a common mains standard. From 1 January 2004 the mains supply should be 230V (-5%, +6%), 50 Hz. ie a range of 218.5 - 243.8V <<<
So if the voltage is above 243.8V where mains enters the house (or anywhere on an *unloaded* circuit, you have cause to complain.
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Dave Fawthrop < snipped-for-privacy@hyphenologist.co.uk>
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On Sat, 29 Jan 2005 11:13:16 +0000, Peter Scales
The indicated

Sorry this is wrong. The voltage used to be specified as 240 V 6% however a few years ago, in order to harmonise with europe, the specification was changed to 230 V +10% -6%.
You will notice that 240 +6% is virtually the same as 230 +10% so in practice very little has changed and the electricity suppliers keep the average voltage close to 240 V.
Russell.
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On Sat, 29 Jan 2005 10:34:52 +0000, Kevin Steele

It's a sad fact that the life of incandescent bulbs is extraordinarily sensitive to supply voltage. When operating somewhere near rated voltage, the life of typical gas filled tungsten filament lamps varies as the THIRTEENTH power of the RMS value of the applied voltage!!
This is an empirical figure and it varies a bit with lamp design but it is still a fair basis for estimating lamp life. If operated at constant current instead of constant voltage the position is even worse - the TWENTYFOURTH power of the current. The operating conditions of a single lamp in a chain of Christmas tree lights is closer to constant current than constant voltage and this contributes to the depressingly frequent failure rate of this type of lamp.
Based on supply voltage, it only needs a 5% increase or decrease to halve or double the service life so it's not surprising that lamp life can be a pretty variable quantity.
The voltage can be checked at any convenient power point but unless you're using a very expensive professional instrument +/- 2% accuracy is about as good as you can hope for. Most 3 1/2 digit digital meters can achieve this but, because of the venerable age of most of the well respected AVO 7/8 analog meter series, they need to be fairly recently calibration checked.
Both types of meter actually respond to the MEAN value of the AC waveform (the average of all the instantaneous values ignoring polarity) but they are calibrated to read the equivalent RMS value assuming the waveform to be a pure sine wave.
Adding to other comments in this thread.
If voltage is your problem I would expect it to be longer term variations rather than transient spikes simply because serious spikes would be trashing your electronic equipment before they had much effect on the thermal time constant of a lamp.
I can't think of a good reason for shorter lamp life in multiple lamp fixtures other than the obvious comment that a triple lamp fixture is likely to fail three times as often as a single lamp.
From all points of view replacing incandescents with modern fluorescents is an excellent solution. Life is very much longer and less affected by minor voltage variations. They are slightly affected by frequent switching although, compared with the failure rate of incandescents, this is a pretty minor effect. There is an EXTREMELY small amount of emitter degradation during the first second or so after each switch on until the lamp has reached stable operation. The cumulative effect of these multiple degradations can cause the lamp to fail eventually by failing to strike.
This is the thinking behind Tim Leeches 'keep it on for twenty minutes' comment. However the emphasis is slightly different - it's not that it's important to keep the lamp lit for twenty minutes - the very small damage increment occurs in the first few seconds after switch on. It's just that there is no improvement in life to be gained by switching it off if you're going to need it on again in the next half hour or so.
With normal domestic switching intervals fluorescent lamp life is so long that switching off is almost always best determined on the basis of power saving.
Jim
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On Sat, 29 Jan 2005 14:20:50 +0000, snipped-for-privacy@yahoo.com wrote:
| It's a sad fact that the life of incandescent bulbs is | extraordinarily sensitive to supply voltage. When operating | somewhere near rated voltage, the life of typical gas filled | tungsten filament lamps varies as the THIRTEENTH power of | the RMS value of the applied voltage!!
Agreed! I saw the graphs long ago.
| I can't think of a good reason for shorter lamp life | in multiple lamp fixtures other than the obvious comment | that a triple lamp fixture is likely to fail three times as | often as a single lamp.
IME It just *seems* like three times the rate, because you have to get the steps out three times as often. | From all points of view replacing incandescents with | modern fluorescents is an excellent solution. Life is very | much longer and less affected by minor voltage variations.
Another good reason why have replaced all our incandescents with Long Life bulbs. Except for the garage where they get little use and Long Life bulbs may be nicked. Also the loft which is little used.
| With normal domestic switching intervals | fluorescent lamp life is so long that switching off is | almost always best determined on the basis of power saving.
We leave our flourescents on for hours as a security precaution.
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On Sat, 29 Jan 2005 14:20:50 +0000, snipped-for-privacy@yahoo.com wrote:

Two spring to mind - one is that very often lamps in these fittings are not vertical, the other that they will run hotter.

Not quite all - they don't work with dimmer switches. I fitted dimmers to four rooms in our house when rewiring 15 years ago [frightening that it was that long :-( ], now only one can be used.
Maybe you lamp experts can answer another question - these dimmers have 1A fuses built in to protect the contents. More often than not, when a bulb gives up the ghost this fuse blows. What is happening inside a filament lamp when it dies which will cause this?

The 20 minutes thing was based on correspondence my father had with, IIRC, GE lighting when he was having problems with short lifespan of mini fluorescents a few years ago. ISTR a paper in the IEE journal being quoted. I'll ask him if he remembers, though his memory at 91 isn't quite what it was. Still better than mine sometimes <g>

Cheers Tim
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