Mains voltage 275v??

[Steviecuk]

Hi all. I have just installed some lighting in my lounge which is a mixture of LED tape via a dimable transformer and LED GU10s all run through an LED comparable dimmer switch.

Information that you might need to know.

I have removed the original light fitting in the middle of the room and connected the loop through and patched the whole up. As I am using a transformer for the LED tape and wanted to add a plug socket in the loop for something else, I decided to run the power to the new lighting run from a fused spur that was on the back wall. The fused spur is on the main downstairs socket loop and because of this and because I was fitted a plug socket with the run, I used 2.5mm T&E for the run (nightmare trying to get it into the GU10 holders)

Everything has been working absolutely fine for about two weeks until I noticed the LED tape not working this evening. I have checked the tape and it is not receiving its 12v and is steady at 0. I then removed the transformer cover and measured nothing on the output side, however measured 278-282v on the input from the dimmer. I measured direct from the dimmer and the input to the dimmer is the same. When the dimmer is low the output voltage is 105v.

My question is why the hell do I have 278-282v going to the dimmer and in turn to the transformer? The transformer is rated up to 240v which I'm guessing would have a little bit of leeway but probably not up to 280v and I am presuming this is what has blown it. I have measured a plug socket on the other side of the room but should be on the same loop and that is measuring 253v.

Can anyone tell me why there might be this stranger higher voltage?

Thanks. Steve.

 

[Richard Burns]

If you have dimmers involved they give a very mixed waveform and it is possible that is the dimmer were disconnected from the supply and then the supply voltage measured it would be the same as the other socket.
Transformers may not register an output voltage if there is no load, but an LED driver shoudl give a voltage.

253V is at the very top limit of the permitted voltage range for supply so there might be a problem with the supply voltage.

If you are not using a TRMS meter then the results maybe skewed if there is variation in the supply.

However the high voltage could have damaged the transformer, they shoudl be able to cope but may overheat.
As another thought is the transformer a dimmable one, if not then it may have just burnt out from the variable dimmer supply.

 

[Steviecuk]

Hi Richard thanks for your reply. Yes it is a fully dimmable one and running at just under its 48w capacity as they advised. I'm only using a standard Maplin jobby multimeter its not a TRMS one.

 

[Steviecuk]

I have done a bit more measuring and found this...

The fused spur is measuring 250v. There is then a 5m run to the plug socked that I put in which is showing as giving out 290v!!!!!!! The cable then runs to a junction box with a switched live going down to the dimmer which is measuring 280v. WTF!?!?!? How can it be 280 or 290v at the end of the loop but only 250v at the beginning?

 

[Richard Burns]

It cannot be, there are errors in your measurements somewhere.

 

[dmxtothemax]

The meter is reading hash on the line ?

 

[NDG Elecs]

Inverse volt-drop..... obviously!!

I think checking it with a decent voltage indictor and MFT (for confirmation) would make sense. As Richard (and indeed the OP) say, it does not make sense at all!

 

[dmxtothemax]

use a good old fashioned anologue volt meter !
low impedance is best.

 

[Steviecuk]

Thanks for all your input. I am going to restart this tomorrow and take everything I can off the run and measure it bare at all points and see where I stand then and if it stabilises. I will let you know my findings and hopefully might get somewhere. Thanks everyone.

 

[Wilko]

Hi Steve - agree with all that a "real" 280V rms would seem unlikely (and not good for the long life of anything attached to it). Likely it's a measurement problem and needs to be ruled out. Another thought from post #4 is maybe your 5m of new cable is floating at some weird induced voltage shown on your meter. So I'd safe isolate the whole installation and reconfirm continuity of new conductors. I don't mean to tell you how to suck eggs, but this stuff can kill you.

 

[Steviecuk]

I have isolated it from the spur which was the start and I'm going to take everything off so there's no load and measure it all again.

I have made this diagram of how I have done it, can you see any issues from it that may have caused this issue?

The one thing I was questioning when installing was does it matter that the neutral is shared in this way between the two types of lighting?

 

[telectrix]

i would have fitted a 3A or 5A FCU after the single socket.saved using 2.5mm to the LEDs. the N is OK as it's all part of the same circuit.

 

[Steviecuk]

Damn I didn't think of that telectrix. Had great fun trying to piggyback the 2.5 in the GU10 holders. Lol.

Oh, that's why I needed up putting the neutral like that because I though no matter how you do it, the neutral will still be connected to everything in some way. I have just taken some more readings with all tranny's off and got the readings on the picture.

I've also just checked every socket in the house and they are all measuring 270v!?

 

[Wilko]

Hi - 270V is a worry, but likely it's your meter. Can you get access to a calibrated meter? If it really is 270V then your DNO needs to be told so they can attend to it. Here's a list ...
ENA - Electricity distribution map - http://www.energynetworks.org/info/faqs/electricity-distribution-map.html

 

[Steviecuk]

I have now tested the sockets with my install completed isolate and removed from the loop and the sockets still read 270v on my meter. The 270 would kind of make sense as I have taken the transformer apart and the input side has overheated and blown. (Gotta love the smell of a blown cap)

 

[Steviecuk]

Hi - 270V is a worry, but likely it's your meter. Can you get access to a calibrated meter? If it really is 270V then your DNO needs to be told so they can attend to it. Here's a list ...
ENA - Electricity distribution map - http://www.energynetworks.org/info/faqs/electricity-distribution-map.html

I have just called them and they are coming out to check the supply. Said it's more common than you'd think.

Thank you everyone, hopefully they can resolve it. Will post once they've been. Thanks.

 

[Steviecuk]

Just had the guy round who tested everything and turns out it is that my multimeter is crap. Measure 248v from several different places including the main in box. He checked the trans and it is only rated 200-240v which he thought was strange for UK ranges and should be more like 220 or 230 +10%/-6% so could be why it has blown. Going to get onto them now and see what the tranny company say.

Thanks everyone again.

 

[telectrix]

first check the voltage at the CU, on the incoming terminals of the main switch. hopefully your meter leads have sufficient insulation. if it's above 250V, then beg, borrow, or steal a decent meter to check.

edit. scrub that. just seen last post/s.

 

[Steviecuk]

hopefully your meter leads have sufficient insulation.

LOL. 'hopefully'. Well you wouldn't get many replies from me afterwards if they didn't.

Just called the transformer company and they said they have never heard of mains voltage being anything above 240v. Either way I'll be getting a refund and I'll have to source a better one with a more suitable voltage range.

 

[telectrix]

i can't see 248V being a problem for that tranny.