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[UK] Electrical Supply help


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#1 AJB2K3

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Posted 24 March 2012 - 09:37 AM

I expect this is not the place but I need help please and it's got nothing to do with Netduino projects. Since the house was so called rewired we have constantly had bulbs blowing (being cheep bulbs we put it down to that) how ever I've just received some new leds replacements and found the supply to the lights had dropped to 3vAC (as apposed to normal 230V ac) I expect one of the cables is responsible but I just want to check if I'm on the right track). I wish I hadn't thrown away all by Electrical course note but they we all hand written!

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#2 Mario Vernari

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Posted 24 March 2012 - 10:03 AM

I don't understand what's the actual question, but I'm suspecting about the reason for so low voltage. It's quite impossible that you have 3VAC across the mains. It's so powerful that you much easily melt the house wires instead of dropping the nominal voltage. That's for sure. I suppose that the leds aren't powered directly by the mains, but instead via some adapter (e.g. a transformer). Moreover, since a led is a diode, it's easy that the voltage is DC, and not AC. Could you explain better the problem, and how did you measure the voltage? Cheers
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#3 AJB2K3

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Posted 24 March 2012 - 11:08 AM

Sorry, the leds are mains powered (230/220V AC or whatever there pumping through uk lines nowadays) Whet the last bulb blew it looks like it took out the supply to the wall light cables (haven't lifted the floor boards yet but the main room lighting circuit that the wall light are attached to still works) I'm wondering if what i'm detecting (using my fluke 111 electrical test meter) is induced voltage.

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#4 Magpie

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Posted 24 March 2012 - 11:38 AM

Hi Do you have smoke alarms? If you dont you should get some, even though they are annoying. Like Mario I find it difficult to see how a blowing light bulb would take out a circuit breaker. I am not saying it didn't happen but it's hard to understand. The only reasons I can think of for overvoltage on your mains are line surges or a broken neutral. Broken neutrals I would say are quite uncommon but can have serious consequences. If you ring up your supply Authority and say you suspect you have a broken neutral they might come and inspect for free. Can you get a second sparky in to verify the safety of the installation, especially the neutral and the earth connections, don't get the first one he may be dodgy, I would say it might be two hours work. Otherwise can you just turn off any dodgy circuits, at the switchboard and see if the rest of the house is ok? I wouldn't be getting the multimeter out unless you know what you are doing, and you are in a clear state of mind.
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#5 AJB2K3

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Posted 24 March 2012 - 11:43 AM

Its not over voltage, its under voltage UK=220-240!
I've got the supply working (when they rewired the celing fan,it didn't get fitted properly and mashed up the wires, cleaned up that mess and have a supply but looks like the contacts in the wall fittings are fubar (cannot get them to contact the new bulbs!)

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#6 Magpie

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Posted 24 March 2012 - 12:21 PM

Yes I did see you said undervoltage, I just made a big presumption that only overvoltage will take out the light globes. Anyway hopefully you have found the cause of your troubles. Good Luck
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#7 AJB2K3

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Posted 24 March 2012 - 03:18 PM

Thanks, the cable was one side, cheep chinese led bulbs being the other. I think the tip is too short for an E14 fitting!

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#8 Bainesbunch

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Posted 24 March 2012 - 07:30 PM

OK so trips WILL blow when a light bulb finally fails sometimes. This is cause by the surge current that is drawn at the time the element fails. In a normal incandescent light bulb the filaments are double wound. Sometimes these short out, because the bulb is knocked or the filament starts to stretch and fold back on itself. This causes a much lower resistance through the bulb. This in turn then causes a momentary high current to be drawn just before the bulb fails. A low current trip like 5 amps normally found in UK domestic lighting circuits will trip quite easily. If you are measuring the voltage in series with your LED light then it is quite possible that you are only seeing 3 volts due to the internal resistance of the LED light. Cheers Pete.
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#9 nakchak

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Posted 28 March 2012 - 08:21 PM

Speaking as a former sparky sounds like a number of things Firstly cheap bulbs like cheap batteries are often a false economy often poorly made and prone to blowing Secondly if you are measuring 3vac between bulb socket terminals something is seriously amiss and you should get annother electrician in to verify everything is ok, I am surprised that none of your breakers blew, it is possible that a loose connection is to blame again get it checked as poor connections can lead to arcing which can destroy switches and more seriously if your breakers are not tripping potentially a fire. Hopefully its just a case of cheap bulbs and poor.manufacturing tolerances but if you suspect the wiring get it checked as the cost of an electrician is a lot less than the potential.damages to your home or even worse your family.




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