Downlight connector blocks melted

[Smugley]

Hello all,

Went to fix a problem last week: 'lounge lights not working'. Found 7x50W ELV downlights had been installed with individual 20-60W transformers wired off a single 400W standard dimmer.

The dimmer had blown, along with most of the transformers and on nearly every light fitting, one of the two connector terminals on the 12V side (i.e., that between the transformer and the lamp holder) had overheated and melted the surrounding block. The fittings were safely located away from joists in a generous ceiling space with no insulation.

I replaced all the transformers , along with the connector block 'stand-off' holders and the dimmer and installed 35W lamps and labelled each fitting 'MAX 35W'.

I haven't seen this much damage before in a single circuit and was trying to deduce the sequence of events which led to this. Obviously most people would agree that loading 350W onto a 400W resistive dimmer is overload. Some even won't load more than 50%. Do you reckon this was the only cause or may have there been another factor involved?

 

[malcolmsanford]

ELV downlighters do tend to run hot, hotter than the LV ones, so heat damage to fittings and connector blocks are wide spread. Also you find that the actual lamp holder can also get damaged and leave the lamp loose in the holder and so not lighting.

The lights would most likely come as a kit and not be of the highest quality and so again it is just a matter of time for them to fail, you may find that the transformers failing could have burnt out the dimmer.

Newer more expensive dimmers apparently do not now need the 50% downrate, but very few people will want to pay 100+ pounds for a dimmer, so I would if using a cheaper model still downrate, as the cost between a 400 and a say a 1000 is not that great.

Bottom line to all this though ......................the things are bloody useless for lighting in general, and for some unknown reason the UK public have no problems in putting into their ceilings miniature fires.

 

[mogga]

Halers EVOLVED would solve this PMSl I H8 elv trannys for the exact reasons malcom has listed and the general Joe Public sees "Dimmable" and 400w on dimmer adds subtracts multiplies and then decides thats ok ill just fit them without realising some of the damage that can be done by incorrect fitting of 12v( safer than 240v in their minds) its been proved time and time again ELV + gen public + no knowlage= BIG DANGER of fire . The sooner restricted sale of electrical equipment is brought in the better for all of us ( apart from the loss of work due to numptys )

 

[Smugley]

Thank you both for your replies. This rented property is incredible. The entire three story 4 bed house is covered in 12V downlights. Not a single other type to be found, including 20x20W small halogens in the kitchen (also run off a 400W dimmer!). I've already had to replace 41 halogen lamps, 19 transformers and two dimmers and still have two rooms to go. No wonder they have three 10A lighting circuits.

 

[Dunc]

The main reason for the terminal blocks melting is generally two fold. The first reason is cheap terminal blocks and the second reason is the installer not checking the pre terminated side of the terminal block (the bit to the lamp holder) for tightness. I have never had this happen personally but that's because i tighten all terminals properly and replace any terminal blocks that have stripped threads or split under strain which is common with cheap products.

 

[Smugley]

Thanks Dunc. Good point about the factory terminations. Odd that in every case it was only one and not both of them.

 

[Dunc]

Thanks Dunc. Good point about the factory terminations. Odd that in every case it was only one and not both of them.

Again it's not uncommon in my experience, it only takes one loose connection to generate a large build up of heat leading to melted plastic. The thing people seem to forget is that there is just over 4A running through that terminal block on the ELV side of things which is near enough the capacity of the connection. It's no surprise that loose connections lead to such damage.

 

[Smugley]

Indeed, I always check tighness of all factory terminations too, and I've seen a few transformers straight out of the box where the ferrule is hanging on by only a few strands of copper.