4-20ma Cabling - 3Wire

I assume you are talking about sourcing or sinking switched digital signals otherwise known as "volt-free contact" (VFC) type signals, rather than comms (which would require a separate twisted pair cable normally_?


It's not recommended to run that type of switched digital signal in the same cable as 4-20 mA loops as the VFC affects the 4-20 mA signal, especially 3-wire.


In the main, volt-free contact signals are usually run in the equivalent of the "3-wire" type arrangement (common + switched).


If you have to run them in the same cable, they should be separated by a screen - 2-wire approach recommended and each twisted pair in its own screen. The only exception to this is if you're using actual relay contacts/coils rather than semiconductor source/sink, as these can really foul up 4-20 mA signals, (and comms).

I assume you are talking about sourcing or sinking switched digital signals otherwise known as "volt-free contact" (VFC) type signals, rather than comms (which would require a separate twisted pair cable normally_?


It's not recommended to run that type of switched digital signal in the same cable as 4-20 mA loops as the VFC affects the 4-20 mA signal, especially 3-wire.


In the main, volt-free contact signals are usually run in the equivalent of the "3-wire" type arrangement (common + switched).


If you have to run them in the same cable, they should be separated by a screen - 2-wire approach recommended and each twisted pair in its own screen. The only exception to this is if you're using actual relay contacts/coils rather than semiconductor source/sink, as these can really foul up 4-20 mA signals, (and comms).