DIY Doctor UK DIY Forums

Hi

New to the forum but lurked for a few years.

About 12 years ago I installed a set of starlights in the kitchen running off a 12v transformer.

A couple of months ago the lights started playing up and eventually stopped. Once I'd cut a larger hole to access it (couldn't do it from above as that floor is tiled and with underfloor heating) I found that the live side of the connector block was black from the plastic melting and the live had come away.

The void has nothing obvious that could have been in touch with the connector and lucky that it was not in contact with a joist.

From what I can see of the transformer there is no sign of heating or other damage, same with the lighting wires and fittings.

Any clues why it would burn away after all these years? Could the transformer be faulty and sending power surges through? No fuse has ever blown on the lighting circuit.

Likely causes are loose connections, was the terminal bloke enclosed in an insulated box.

No, not in a box but I would have thought a loose connection would have shown itself a few months, a year later but 12+ years?

Firstly the terminal must be enclosed in an electrical insulated enclosure.

And connection can become loose overtime and loose connection do not also immediately become apparent.

Loose connections cause arcing, this can occur on both the live and neutral sides.

Electrical flow does pulse vibrate and can cause screw terminals to loosen over time, also any resistance or stress on the cables can cause cables to become insecure and loose.

The main reason for connection blocks to melt, is down to arcing of close contact/proximity to heat. The other reason is if they are not correctly rated for the current carrying capacity required, but with an correctly installed lighting circuit, this would be rare.

There is a reason why connections which can not be accessed have to be maintenance free, Vibration and heating and cooling will cause screws to become lose. It starts with vibration then as a result there is a poor connection then the wires heat and cool and if you do check them you would swear the person who did the job did not tighten them to start with.

If any connection can be affected to reduce its grip then every connection in the house or workplace needs to be periodically checked I would have thought. Yet there is nothing in place to command that it happens.

In my case the only way to access the connections would have been to rip up a tiled floor with heating or cut into the ceiling which I had to do.

I agree that electrical connections need to be correctly housed and in these lights with LED versions 240v I have housed them correctly. This is a practice I started a few years ago but not at the time when I put that lighting in.

Interestingly these new lights had screws that I could tweak a bit more without overdoing it. If I had not checked would the same have happened in that fitting but caused by the manufacturers QC or tolerances?

The regulations now in place, are that any joint or junction that is not accessible must be constructed in a maintenance free method.
It is always wise to reduce or prevent if possible any junctions that cannot be easily accessed for inspection, test and maintenance.

Back in the day, it was accepted that standard junction boxes could used but not now. When I installed I very rarely use junction boxes, I avoid them if I can.