Careers: Engineering & Electrical Trades/Wire return system


I'm having a hard time trying to learn the main differences in a 3 wire return call system vs a 4 wire return call system. Google isnt helping very much. As far as i can tell the only difference is the wiring. The only advantage on a 3 wire i can see is you use less materials possibly. Could you please explain this?

Need more info.  A three wire return call system has one battery, two SPST pushbutton switches, two bells, and a three wire cable between the two locations.  It can be changed to use only two wires between locations (i.e. a two wire return call system) if the switches are changed to SPDT.  But I'm not sure of what you would call a 4 wire return call system. Does it have more than two locations?  Or maybe more than two bells (or lamps, etc.) Do you have a schematic?

Hope this helps!


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Dave Nyce


I have been an electronics engineer for more than 25 years. I can answer questions on analog and digital circuits, and my specialty is sensors.


I am the inventor on 23 US patents, and also some foreign ones. Developed sensors for over 25 years. Licensed airplane and helicopter private pilot, have HAM radio license.

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