From: arl_123234@hotmail.com   
      
   On 1/25/20 2:17 PM, Grant Taylor wrote:   
      
   >   
   > I think I read where POTS telco systems started with negative ground and   
   > then switched to positive ground to combat corrosion.   
   >   
   >   
   >   
      
   Yes, I think that's correct.  The only other reasons for earthing a CO   
   battery terminal I can come up with were to support ringing-to-ground on   
   party line systems and as possibly a shunt path for lightning strike.   
   In the real old days of military field telephones, the Army would   
   sometimes utilize a "simplex" circuit to allow a ground-return telegraph   
   or telephone circuit to be superimposed on a full metallic telephone   
   circuit. (Don't think that was used in commercial practice, though.)   
   Sincerely,   
      
   --   
   J. B. Wood	            e-mail: arl_123234@hotmail.com   
      
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