Electrical HV and instrument signal cable segregration

I need to know what is the acceptable distance for segregration of electrical HV voltage cables and instrument signal cables. Both cables are to be run on separate electrical and instrument trays.

Please also code with standards/NEC.

Also, is 24Vdc power supply for field instruments considered as electrical or instrument cables?

So you're letting other engineers do the research for you, eh? I think I can point you in the right direction, but it's up to you to do the research. Check out API RP 552, Section 5.2.6, for the proper segregation of instrument cables from HV cables.

Regarding your 2nd question, in design engineering, power supply cables for instruments are naturally called instrument cables. Why? Because firstly, it is instrument engineering who will be responsible for cable specification and cable routing and termination, etc., not electrical engineering. Secondly, the 24 VDC will be coming from the DCS UPS distribution board, which is still under instrument engineering responsibility. Thirdly, it will be supplying instruments, not electrical equipment.

Hi,

On a separate tray it should be far enough away, e.g. 9 - 12". It is quite common to use the same tray with a metal barrier for separation. I don't think its the high voltage so much as high current that causes noise by magnetic coupling. Most high voltage cables are armoured and your instrument cable will be shielded so the capacitive coupling is minimal. Noisy loads like VFDs are probably more of a problem. It's important to make sure that your instrument shield is only grounded in one place (usually at control system), otherwise you can get current flow (ground loop) from one part of the plant to another which induces lots of noise. You can't always avoid mixing the cables, but in my experience it is seldom a problem.
The 24Vdc power I would consider as an instrument cable, after all if you get noise in that it will get into all your loops.

Sorry don't know the standards/NEC.

Roy
Instrumentation Consultant