MCC Control Supplies

I respectfully disagree. Any 3 phase motor if on a properly designed circuit, will fault due to single phasing of that motor. Also most resistive 3 phase circuit will also have controls with the same purpose. 3 phase circuits do not have to have their control on the same polly phase. I have had times when technicians insist on using the first and second phase for control. That is my take on the point anyway.

Physically, Red and Blue should be further apart, this will minimise any chances of a potential short circuit.

I was told once that it was easier to add auxiliary contacts "outside" the red and blue phases since the white phase was in the middle and posed a greater difficulty to access. Seemed fair at the time but I seriously doubt there was any real scientific reasoning behind it.

For under/over voltage/frequency & phase failure/reversal etc there are "multi-function" relays.

Yes, and how does this help to explain why red / blue phase connection is "chosen" for control circuit energisation?

You're normally on the ball Pnaban...have you skipped your meds today?

Irrespective of in which phase(s),control supply is taken,if there is any kind of voltage problem there should be trip of main breaker.

Some old 2 phase systems I worked on were phase coloured red and blue so it may be a carry over from 2 phase to 3 phase supplies. Probably the same reason I was told to reverse motor rotation by swapping the red and blue so the markings still read r/y/b

I cannot answer your question directly, but I would like to draw your attention to the fact that each phase colour is only really a marking. It does not mean that the red phase in one building/area, is also the red phase somewhere else......

It basically only demonstrates the rotation.......

I am sure that with modern equipment it is probably now possible to get the red phases everywhere to be the same phase, but years ago, when many cables were laid, was it possible to identify, 100% accurately, each individual phase? I somehow doubt it....but that is just me maybe......whats your take?

Yes sort of.

So long as the rotation is correct it doesn't matter what the order is.

I have come across legacy distribution networks where the phases at different load centres are not identically marked but the rotation is correct, mostly at least....it meant that the rotation had to be checked before committing to a termination of a load. eg if all the feed conductors are black and identically embossed or otherwise marked.

In new installations keeping the phase reticulation identical throughout the distribution network makes for easy commissioning and relatively idiot proof load connection.

Rotation direction is more important than consistent identification.

Great post, I agree entirely.

You don't always have RYB sometimes often you encounter RWB.

White is often used to mark neutral. So going with RB eliminates reduces the possibility of blunder. As a previous poster mentioned it may just be a hang over from 2 phase reticulation colour conventions.