corroded copper wire in a G4 lamp assembly

[Adam Funk]

This is the inside of a kid's hanging night-light that shines planets & stars over the room. It started acting flakey & I figured out that there was a bad connection behind the G4 holder itself, so I removed it, bought a replacement (disc with 2 slots & wires coming off the back), & figured I could chop a bit off & solder the new lampholder onto the good cable.

Well, I chopped about 1 cm off with a rotary tool & found cruddy wires. I chopped another cm off, & found more of the same. Any suggestions as to why they are corroding or how to approach this are welcome. (Otherwise, I'll just chop off some of the wider piece & keep going.)

Thanks.

[Andrew Gabriel]

My guess would be the use of cable which is unsuitable for the temperature, and the insulation is breaking down into components which include something corrosive.

I've never bought anything with a G4 fitting in it (the poor efficiency would put me off), but high temperature ceramic fittings normally have tails attached with high temperature cable, as stranded copper with PVC insulation would fail.

[newshound]

+1.

You do, occasionally, find bits of old PVC flex where the copper (after stripping the insulation) is almost black for a good number of centimetres from the open end. More common in "damp" environments like outside lights, but not exclusively. I have always assumed it's caused by poor manufacturing.

[Brian Gaff]

Yes, thinking the same. I saw one which had some almost unbendable stuff on the inside of the lamp and that itself terminated some ing ches of the hard cable later in a conventional connection block inside the housing. In this case it was a pretend oil lamp but did get quite hot!

I'm assuming the smi rigid extensions were high temp cable. Brian

[Brian Gaff]

Actually that black effect happens to most wire eventually. I have a long bit of pvc wire as an aerial and it too is kind of sticky and black when stripped, but aan be soldered if cleaned up a buit. I'm not sure of the mechanism, but heat cold and dampness obviously do not help, nor does the sun, not applicable in your case I suspect. My suggestion eithe way is a new bit of cable, and possible if there is room a short bit of high temp stuff to a block inside first. Brian

[Adam Funk]

I think you're right. It doesn't show well on the photo I provided, but I slit the whitish covering (that looks like the heat-resistant sleeving you often get with light fittings) & there is a gap between that and the cruddy copper where non-heat-resistant insulation might have been. I'm surprised that this problem happened with just 20 W hanging in the middle of a reasonably large ball of air, but I'm wondering now how to fix it properly.

I think the tails on the G4 holder I've bought have something printed on them. I'll copy that down & look it up.

[Adam Funk]

OK, the tails on the G4 holder say "300/500V 180°C" --- that should be good enough?

(In full, "HAO CHENG ELEC.APPL.WIRE & CABLE CO. LTD. Nr 40017754

300/500V 180°C H055K 1X0.75mm2")