Electrical and Instrument Cable

Yes.

Yes.

100 what? Mm? Cm? Meters? kM? Inches? Feet? Cubits? What do you mean by armored? Does that mean shielded?

Do you feel that you are qualified to be making these kinds of decisions if you must ask those kinds of basic questions? I'm not trying to be rude, but it appears as though you are not an electrical engineer and are trying to set up something rather complex (instrumentation) without even the most rudimentary knowledge necessary. That means that if we help to facilitate this, someone may get hurt. Hire a qualified electrical engineer please.

If I well interpreted these sentences no distance is required from power cable[low voltage] if the ITC cable is armored. However the armor has to be well grounded[see NEC Art.250].

According to NEC Art.727.2 Definition.

Type ITC Instrumentation Tray Cable. A factory assembly of two or more insulated conductors, with or without a grounding conductor(s), enclosed in a nonmetallic sheath.

Art.727.4 Uses Permitted.

(7) Direct buried where identified for the use.

Art.727.5 Uses Not Permitted

Type ITC cable shall not be installed with power, lighting, Class 1 circuits that are not power limited, or non-power-limited circuits.

Exception No. 2: Where a metallic sheath or armor is applied over the nonmetallic sheath of the Type ITC cable.

As per IS 1255, the minimum clearance should be 300mm.

I did not find in IS 1255/83 ch.6.3.3 " Clearances" a reference to the minimum desired clearance between power and instrument cable (laid in ground).Control cable is not an instrument cable and-with some exception-control cable in Switchyard-is not shielded or armored.