[Gllug] ADSL on BT phone wires

[Chris Bell]

On Thu 17 Aug, Ryland, Peter wrote:
> 
> On Wed, 2006-08-16 at 22:29 +0100, Christopher Hunter wrote:
> > On Wednesday 16 Aug 2006 13:34, Andy Farnsworth wrote:
> > 

> Loss via ground?!  It's an almost perfect conductor.  Resistance is
> inversely proportional to cross-sectional area, and the earth's is
> enough to guarantee that it performs better than copper wire.
> 
> Earth: ~0.00005 ohms/m
> Wire:  ~0.01 ohms/m (for 2mm-thick copper wire)
> 
> Pete

   That depends on local conditions. Phone users with a party line often had
to rush outside and pour water over the BT earth spike to get their phone to
work. Water is not retained on sandy or rocky ground, and the water table
may be a long way below the surface, giving high resistance except just
after rain.
   Every time we worked on location we had to ensure that there was an
adequate earth spike, for both electrical mains and lightning safety
protection. We had a limited length of heavy earth cable, and often the only
choices when we were parked on concrete or tarmac were to drop it down a
drainage gulley (it conducts well as far as the U-bend) or place it under
the lorry wheel (pretty useless, but it looks good).
   We always had an earth to the power supply, but on one occasion that was
a hired 1 Megawatt generator that had been used for 110 volt lighting power.
We had been connected across the 240 volts output, but the generator chassis
and earth spike were still connected to the centre tap. Nothing went bang
because the vehicles were parked about 50 yards apart, but people were
complaining about tingles as they grabbed door handles.


-- 
Chris Bell

-- 
Gllug mailing list  -  Gllug at gllug.org.uk
http://lists.gllug.org.uk/mailman/listinfo/gllug