ADSL modem plugged into socket where there's no phone.

[Keith_Beddoe]

@WSH 

Of course it would affect FTTC in the local serving section.

When I am moved to DV, and I lose the 50V from the exchange, I may inject a small voltage across the line, if I get any issues.

It would be interesting to know on FTTC,  if there is any DC path back through the port in the cabinet, as the injection of a small current through that path, may improve the reliability of the connection.

On ADSL, there may also be a DC path through the MSAN,

[WSH]

@Keith_Beddoe.  Again, thanks for that.

I get the impression you worked for OR but I wonder what would be Openreach’s view be of customers injecting voltage to their line?  I would have though it would already be being done if it was going to ward off significant problems?

@HHGTTG.  Oops, sorry I seem to have hijacked your thread a bit here…I’ll clear off now.

@Crimliar.  Again, thanks but I thought that was the same as I said at the start?  I’m a retired IT tech myself so, without wishing to sound arrogant, you can take it the internal wiring is not the issue.

[Keith_Beddoe]

I get the impression you worked for OR

@WSH 

Yes I worked for GPO, Post Office Telephones, BT Wholesale and Openreach, nearly 42 years in all.

A lot of time was spend on Private Circuit Repair, and it was standard practice on analogue circuits, to apply "DC Wetting" https://en.wikipedia.org/wiki/Wetting_current

This was to overcome any oxidisation of relay contacts or interception "break jacks" used for testing. Its was only a tiny current of about 5mA which was injected via the line transformer, and was very effective.

Now that we are passing digital signals over copper wires, without any DC component, problems are going to occur, and are not going to be easy to locate.