Multicore cabling

[Lc1]

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 this to stop induced voltages on the other cores?

Thanks

Thank you

 

[lfe]

Any box, door, container ... that has an electrical device, even a simple 24V pushbutton, must be grounded and this cable seems to be used for that.

 

[Liam Moran]

You have not stated what type of multicore it is but if the cores are numbered with 1 unnumbered green and yellow cable then the cable is probably either LIYCY or YY.
The standard core colouring for these cables is for 2 black cores with white numbers for 2 core cable, and for 3 cores and above it has black cores with white numbers all except 1 green yellow.
It is the standard construction for these cables. Depending on what it is used for, you may or may not need the Earth, but if you do it is there and clearly identified.

 

[Lc1]

Thanks for this. The box also has an earth cable connected to nearby steelwork. I was just wondering why use both?


Thanks

 

[JohnCalderwood]

Does the earth core go to an earth terminal, either on the box or on the terminal rail?

If so, then you are connecting from the cable to the box to the steelwork, to prevent any cable fault giving a voltage on the earth core, and potentially you, the user, touching a potential from the box.

 

[Lc1]

Thank you for the replies. I was confusing myself.