Low voltage lighting

[Sparkypezz]

Hi I was called to a fault today were the tenant of the property had 3 brand new low voltage lights (bnq specials) on the under side of the face board of the porch the tenant had tried fitting them himself (never a good thing) and they surprisingly were wired correctly but to the point I checked the polarity which was correct, i visually checked all the cables no damage / compression failures etc but the lamps just would not light so I presumed either faulty bulbs or transformer so i done a voltage check on either side off the tranny for 240 n 12v so on when i noticed i was getting no voltage on the 12v side (figures) but thn when i tested the 240 side i was getting 400v which kinder threw me a bit is this ok ive never come across this before on a domestic lighting cct before? so then i replaced the bulbs and tranny just to check and when I powered up the tranny made a wierd noise an went dead instantly burnt out but no burnt out smell or heat damage, so again to the point would the 400 v destroy the tranny so quick an how am I getting 400v on a 230v tnc-s supply?
Any thoughts or info would help on the matter as I'm looking to be enlightened on it.
Cheers.

 

[Porque223]

Does the tenant have other electrical problems?
It could be somebody careless is screwing around, upstream, or it could be a as yet undiscovered fault in the system.

 

[Sparkypezz]

No supprisingly not I asked the same question as my thought was is there any underline issues appliances being burnt out bulbs blowing all the time etc but the tenant said everything was fine. He had the property re wired about 2 years ago produced a test cert an all seemed fine with the results pal

 

[bernardgreen]

First of all 12 volt is EXTRA low voltage, 230 volt is Low voltage.

If you found 400 volts on what should be 230 volt the first thing you do is ISOLATE and call out an electrician.

I can NOT see you as being an electrian as no electrician would ever connect a 230 volt transformer to a pair of wires suspected to have 400 volts across them.

 

[Sparkypezz]

Yes I am an electrician of ten years and Ill list all my quals if you would like but i went threw all methods and had a spare one on the van so i knew the worst that would happen would be the transformer burning out it was a last resort but as I said it's the 400v on a 230v supply that threw me an was looking to be enlightened on the matter and the first thing I done when I left the property was call the energy supplier and reported the possible fault

 

[JohnW2]

Yes I am an electrician of ten years and Ill list all my quals if you would like but i went threw all methods and had a spare one on the van so i knew the worst that would happen would be the transformer burning out it was a last resort but as I said it's the 400v on a 230v supply that threw me an was looking to be enlightened on the matter and the first thing I done when I left the property was call the energy supplier and reported the possible fault

Do I take it that, before calling the supplier, you checked the voltage elsewhere in the installation and also found 400V?

If so, are you sure your meter is not at fault. I would have thought that 400V throughout the installation would have shown itself (perhaps dramatically) in many other ways than the loss of a few lamps!

Kind Regards, John

 

[Sparkypezz]

Yes tried it on the house ring done a quick voltage check zs the usual live tests to ease my mind and it was fine this is why it threw me that I was getting 400v on the lighting cct and my tester is a megga mft just had it calibrated about a month ago pal so should be ok I done the dead to live tests on two separate supplies and all was fine and as I said mate I phoned the energy suppliers with a possible fault not an actual fault just giving them a heads up if it were
I found it very unusual an as I said before I've never come across this in ten years so thought I would do the correct thing an if in doubt ask some one with more experience
In the words of a mentor you carnt beat experience

 

[JohnW2]

Yes tried it on the house ring done a quick voltage check zs the usual live tests to ease my mind and it was fine this is why it threw me that I was getting 400v on the lighting cct and my tester is a megga mft just had it calibrated about a month ago pal so should be ok I done the dead to live tests on two separate supplies and all was fine and as I said mate I phoned the energy suppliers with a possible fault not an actual fault just giving them a heads up if it were

Hmmm! If the voltage is OK in the rest of the installation, I can't see how the supplier can be to blame for the 400V you're seeing in the lighting circuit! Have you checked the voltage at other points in the lighting circuit?

On the basis of what you've told us, it's incredibly weird. You obviously cannot get 400V from a single-phase TN-S supply, let alone in only part of the installation. Is this a semi- or a terraced property? Is there any possibility that there is some weird wiring 'between properties' that are on different phases?

Kind Regards, John

 

[Sparkypezz]

You know what John I think your right there mate thinking of it I noticed there was only a down stairs lighting cct on the distribution board there was another 1.5 disconnected and tucked into the back off the board and a spare 6 amp Mcb it could be a bit far fetched but he could have took a supply from next door for his upstairs lights through the loft space or some were and maybe a borrowed line or neutral through the up lighting to down possibly makes sense but could be my imagination running wild and it's just mixed wiring between two terrace proprieties ha but if this were true it would surely remain live! And then show a single phase of 230, strange one :s (but needs resolving regardless) wouldn't rule out some form of mixed wiring heard nothing but bad things about the person who rewired the property.

 

[333rocky333]

In a situation like that I would test all combinations.
L to N, L to E and N to E, as your proberly aware if there was somehow two phases there would likely be a substancial voltage from the Neutral wire to earth

 

[Porque223]

The place needs an Exorcist! Maybe two!

 

[ban-all-sheds]

And this thread needs an OP who is able to write properly.