Chemical Cleaning of Blackened Copper Wires.

Does it matter there's an effective layer of insulation between the strands?

I would say yes - unless there's good contact between every strand and the terminal there isn't going to be anything like equal current sharing between the strands - and I don't see how you're likely to get good contact with the inner strand on a typical 7-strand wire in any event - likewise if you're relying on the end of the screw in a tunnel terminal to scrape off the oxide (or whatever it is chemically), it's only going to make contact with a few of the strands. Ditto for any faults if the oxidisation continues along the length of the conductor and say a nail or screw pierced the cable - a few strands alone would have to carry the full fault current and you'd be into an appendix 10 situation.


Of course, smaller sizes of T&E have solid conductors, so the problem is avoided in most common domestic situations.


   - Andy.

Does it matter there's an effective layer of insulation between the strands?

I would say yes - unless there's good contact between every strand and the terminal there isn't going to be anything like equal current sharing between the strands - and I don't see how you're likely to get good contact with the inner strand on a typical 7-strand wire in any event - likewise if you're relying on the end of the screw in a tunnel terminal to scrape off the oxide (or whatever it is chemically), it's only going to make contact with a few of the strands. Ditto for any faults if the oxidisation continues along the length of the conductor and say a nail or screw pierced the cable - a few strands alone would have to carry the full fault current and you'd be into an appendix 10 situation.


Of course, smaller sizes of T&E have solid conductors, so the problem is avoided in most common domestic situations.


   - Andy.