Silicone cable safety

[emeritus]

I seem to recall reading that the wiring of the colour light signalling that had replaced the mechanical signalling when the LT&S (London to Southend) line was electrified in the early 1960's was found to have degraded seriously after a couple of decades' service. I thought it odd at the time as I had thought that it was only rubber that was susceptible to deterioration.

[Techman]

Certainly the mains lead on my late 60s Antex 15 watt soldering iron has degraded. Sometime in the last decade it went 'wet' and sticky, so after giving it a good clean with IPA it's no longer sticky, but has shrunk in diameter and gone hard.

[TrevorG3VLF]

Several years ago we looked at some railway siganalling relays which operated mechanically but did not make contact. The suppliers had changed the wiring to silicone wire and the contacts were insulated with silica. Perhaps that was the problem with my HW100 transceiver.

I think the transfer was by silane.

[sentinel040]

With regard to it being something in the atmosphere around relay bases, this is a country wide problem and can also be found on sharp bends in wiring. Wet and dry wire deg is something I have to look out for when undertaking correlation prior to making design changes. If the wiring is going to fall apart when they come to try to amend things, you want to know about it in advance! Some changes have been abandoned due to the state of the wiring. It seems to be certain wire types that suffer.
73 Ian

[CambridgeWorks]

Trevor, I wonder if that is what makes Weller TCP switches go intermittent or o/c? Not a direct wired connection, as the silicone cable terminates on a small tag strip within the handle. The switch is quite close though.
I recently took my iron to bits and also the cover off the switch. (it had started playing up, often needing a tap on the bench to restore operation). Both contacts looked as if they were made when viewed under a magnifying glass. Some very fine abrasive restored the contact again. Now in almost daily use and no problems.
Rob

[Refugee]

The problem with that is if a fault occurs and the wiring falls to bits when the repair is carried out.

[trobbins]

Going back to post #1 photo, I wouldn't discount that the sheath degradation was not predominantly due to a mix of age, raised temperature, and flexing.

The fuse, and/or plug-socket contacts, could well be providing a subtle local heat source into the active/neutral wires. That form of heating would stress the sheath in the area where degradation is observed, and not show degradation further away from the plug.

[Refugee]

The heating element is small and reads 1500 ohms so there is less than 200ma to heat the terminals up.

[Amraduk]

In that case, I think you should replace the 13A fuse in the plug with a 3A fuse!

Regards,

Dave.

[Refugee]

I did replace the fuse with 3A back at post#1.