Multicore cable earth

[Indy]

Hello,
We have a local push button station going to a PLC in a safe area. There is a 7 core cable connecting the station to the plc.

Core 1 24v
Core 2 spare
Core 3 push button 1
Core 4 push button 2
Core 5 spare
Core 6 spare
Core 7 earth

My question is why is core 7 an earth cable, can’t think what I’m missing? Is it to stop voltages getting induced in the remaining cores?



Thank you

 

[thebard3]

From the nature of the signals you have identified, I would assume that this is either -24V if there is a pilot light or anything else that requires that, or perhaps it is a shield conductor. If it is a shield it would not be insulated. If it's green, the it's just a ground conductor used to ground the enclosure.

Brad Waybright

The more you know, the more you know you don't know.

 

[TugboatEng]

Typically the earth wire is to provide a short circuit path to trip magnetic trip circuit breakers. That is all. One end of the earth wire must be connected to the positive or negative, X1 or X2 of your power supply for this to work.