[Boatanchors] 9V batteries

[Jim Haynes]

On Fri, 12 Dec 2014, Bill Cromwell wrote:
> Yes..any battery or cell has the potential to kill (pun intended).
>
Reminds me of some work in the Bell System in the 1940s and 1950s.
The overhead telephone cables of the day (and underground ones too,
I guess) were made of paper-insulated wires inside a lead sheath.
The lead sheath can develop cracks, letting water in.  With the paper
insulation the water would not spread far from the leak, so there
was a short between wires and between wires and the grounded sheath.

One method to locate the short was use of a Wheatstone bridge to measure
the resistance accurately from the end of the cable to the short.  Then
the distance to the short could be calculated knowing the resistance of
the wire.  There are several different bridge circuits employed so that
they can deal with things like a wire on a pole that breaks and falls to
the ground, or with a short that has some resistance in itself.

More commonly used in cities was a technique of putting a loud signal,
generated by an interrupter, on one end of the pair and then exploring
with an inductive coil, perhaps with an amplifier, along the cable
until the signal was no longer heard, indicating the coil was beyond
the fault.  Since the fault was rarely a solid short they employed a
string of 45 volt batteries in series connected between the cable pair
and ground to try to burn or weld the wires together and to the sheath.

The first time I saw this they were using large (maybe 6x9x12) B-batteries
of 45V each, connected in series and carried on top of a truck.  Later 
there was a test set made for the purpose that incorporated much smaller
batteries inside a protective case and suitable test leads and a meter.