Oxidation of copper wire
I am re-wiring our house and I found some of the positive insulated 5-10amp cables have a layer of black oxide on all the strands for the entire length of the cable.
Does this cause more resistance and if so, is there a danger that the cable might get hotter?
Is there also a chance that these oxidised cables will lead to higher energy consumption and higher electricity bills?
Hi Dan, thanks also for your very expert advice and links.
As I mentioned to Jayeff, I am in Northern Brazil where things are far more lax and sadly often very badly done, which is the main reason that I am doing a step by step re-wire, as I can afford it.
You say that for 15amp and above, you need solid conductor wiring. As the cables will only be feeding a domestic refrigerator, 4 lights and two wall sockets for plugging in tablets, cellphone chargers etc., I have already bought 6mm cable which can handle up to just over 30amp (correct me if I'm wrong).
They will be running from a single phase (positive) trip fuse rated at 20amp.
I chose the multi-strand cable as I have to pull them through some internal and external conduits (using a cable guide) that go through quite a few turns and the solid wire would be almost impossible.
So it would seem that I might have over-rated the amperage, but surely that would be no bad thing?
Regarding the oxidation of the original wiring, I think it might well have been due to very bad workmanship - mixing up of cable thicknesses, very humid conditions (buried in the earth) and also heating up due to overloading the cable.
Is this a good question?