Can you route AC (CTs and VTs) and DC (protection and control) signals in the same multicore cable? 2

[electrical429]

What is the general rule here, because I sometimes see all separate and sometimes all combined into one multicore. I am not talking about SCADA signals, these should be wired through separate multicores, but what about AC (Current transformer secondaries), AC (Voltage transformer secondaries) and DC (protection and control). Should they be all in separate multicores, all combined or AC and DC separate.

 

[cranky108]

You can do it, but I would not recommend it.

 

[RedSnake]

It would not do it, a 230V AC voltage can induce AC voltages even though low current in a unconnected or connected part.
I would never mix DC parts with AC parts in a cable and especially not one that are used for security.
You will not reach the right security level for the system either in most cases.
And you may end up with all kinds of problems due to disturbances especially if they are connected to safety I/O:s with short short-circuit monitoring by pulsing.

Best Regards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[Fischstabchen]

You code get a hybrid cable with fiber or use 61850 for sample values and just run fiber.

Honestly, I would get more nervous about power cables running with control signals than CT and PT signals.

 

[RedSnake]

It is not so much a question about what to be nervous about. ;-)
You would not meet all standard requirements in Europe.
Even if just using one cable are a cheaper or simpler option, before you have been able to secure or measure / prove that you have meet all the requirements for EMC, Safety, and so on the time spent will have costed more then just doing it with two cables to begin with.

SS-EN 60204-1 Safety of machinery – Electrical equipment of machines Part 1: General requirements
4.4.2 Electromagnetic compatibility (EMC)
6.4.2 Sources for PELV
13.1.3 Conductors of different circuits

And then you would have to read at least 20- 30 more of this standards to be sure you have complied with them all.

Best Regards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[electrical429]

Thanks all. Ok, so you need to separate AC and DC. But can you combine VT and CT signals in one multicore or these should also be separated? Would high secondary CT core currents during faults distort VT signals in this situation? Or is it ok?

 

[RedSnake]

Well this is just from my memory so I can't give any references.
I have never seen Voltage transformer and Current transformer parts in the same cable.
If VT ad CT is the same as primary and secondary transformer side, not sure of this abbreviations haft the time. ;-)
One reason for this can be that the earth part in the cable need to be able to carry the whole fault load if there is a short circuit.
Usually there is only one earth part in a multi part cable and they have the same area as the rest of the parts.
In my mind it is praxis to have separate cables for VT and CT, but I can be wrong.

This is a picture of what we use and require when buying equipment.
It is our version on standard EN 60204-1 but this is for potential bounding to avoid EMC.

Best Regards A


“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[RedSnake]

It also becomes much more structured if you choose the right cable type and dimension it according to function.
It is much more difficult to draw a good circuit diagram if you mix different functionalities in a cable too.
"It gets messy"

Keep it simple is my motto.

Best Regards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[cranky108]

Rarely do CT and PT circuits start and end in the same place. So usually we don't do that. Also we use 4#10 for those types of circuits, which rarely allows for mixed circuits.

 

[RedSnake]

Yes you wouldn't want to start using a 10 mm part to a 220V AC control signal to a relay that just needed 1 or 1,5 mm.

/A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein