BT's superfast broadband network 'risks being empty'

[Tim Deegan]

Originally Posted by kwikbreaks

Did the aluminium cable cause any problems with voice? That's all there was when it was used and it was a lot cheaper than copper. I don't think you can blame BT (or was it Post Office Telephones then) for not having a crystal ball or examining goats entrails.

Yes it did cause problems with voice. And no it wasn't Post Office Telephones then, because some of the companies who now make up Virgin also used them.

Yes it was cheaper than copper, which is why they used it. But it doesn't take much technical knowledge combined with common sense to realise that aluminium cable will start to oxidise over time. And an oxidised surface on aluminium doesn't conduct. Believe me, I spent 18 years in electroplating. So I do know about oxidisation and what conducts.

[kwikbreaks]

Copper oxide doesn't conduct either.

The only place oxidation would matter would be at the joints and they need keeping dry for both. Oxidation on the outside of the cable at voice frequencies wouldn't make any difference unless it was virtually all eaten away. Come to that I doubt it would matter at ADSL/VDSL frequencies either as all TV aerials are made from aluminium and they last for donkeys years totally exposed to the elements. ISTR reading that the main problem with aluminium for ADSL is the extra attenuation over copper.

[Tim Deegan]

Originally Posted by kwikbreaks

Copper oxide doesn't conduct either.

The only place oxidation would matter would be at the joints and they need keeping dry for both. Oxidation on the outside of the cable at voice frequencies wouldn't make any difference unless it was virtually all eaten away. Come to that I doubt it would matter at ADSL/VDSL frequencies either as all TV aerials are made from aluminium and they last for donkeys years totally exposed to the elements. ISTR reading that the main problem with aluminium for ADSL is the extra attenuation over copper.

Oxidisation would occur at any point where the aluminium is exposed to moisture and oxygen. This even includes moisture in the air. It isn't possible to keep all joints 100% airtight over many years.

TV aeriels don't even come into this. To start with they work in a completely different way to cables. And secondly, some more expensive aerials are anodised, which is actually controlled oxidisation, and does insulate. So the insulation doesn't stop radio signals.

It was actually a friend who is a BT engineer who told me about this.

[kwikbreaks]

Most phone cable joints are gel packed which does exclude the air and other moisture. As I said it doesn't matter whether copper or aluminium is in use - excluding moisture is essential for both.

My example with TV aerials was just to emphasise that surface oxidation is irrelevant - it's the joints that matter and that is whether they are copper or aluminium. Of course copper to aluminium is especially sensitive due to the potential electrolytic action.

[Tim Deegan]

Originally Posted by kwikbreaks

Most phone cable joints are gel packed which does exclude the air and other moisture. As I said it doesn't matter whether copper or aluminium is in use - excluding moisture is essential for both.

My example with TV aerials was just to emphasise that surface oxidation is irrelevant - it's the joints that matter and that is whether they are copper or aluminium. Of course copper to aluminium is especially sensitive due to the potential electrolytic action.

We are talking about old connections. In many cases the insulation has broken down, leaving the connections open to the atmosphere. Untreated aluminium is far more prone to oxidisation than copper. As I said previously, I do know about corrosion of metals, and how to prevent it. With aluminium, the minimum corrosion protection for any exposed ends would be an Alocrom 1200 or 1000 treatment, and then to be gel packed. Also what are the terminals made of? As aluminium can react with other metals, causing more corrosion.

Copper doesn't suffer from the same oxidisation as aluminium, especially where contacts are made.