[GreenKeys] Loop driver question

[Jim Haynes]

On Wed, 24 Apr 2013, Lester Veenstra wrote:

> 
> I have not tried to prove this, but I suspect the original high voltage,
> constant current, design choice was determined by the need to drive the
> machine from a central office, down a long copper pair.  And I should note
> that on very long circuits, the CO loop would drive a polar relay in the
> machine rather than a selector magnet directly.
> 
And might have transmitted polar rather than neutral.