Phase Rotation

Maybe your plant was wired RTS before by mistake, and all downstream wiring was changed to match the incorrect phasing. Then, when the new wiring is RST, everything rotates backward.

Awkward though it may be, I would try to keep everything RST until the final connections at motor junction boxes. It is a one-time hassle, but probably worth it.

(I have a minor version of this issue right now where I work. It entails changing about three 480V receptacles, one of which is a real bitch because of no wire slack. But once I get past that, smooth sailing for the future.)

Urban legend has it that, because of a pair of crossed phases in a high tension grid, most of the low voltage motors in the Liverpool area have to be reversed so that they run in the right direction. These things do happen sometimes.

Actually, the electrons don't know and don't care whether they are inside red insulation, yellow or blue in pre-2006 cables, or brown, black or white in post-2006 ones.

Turn the motors around.

The works I served my time at originally had its own power station. All phase rotation was BYR on the works, the older plants were 550V.

A new 11KV grid supply had to be reversed to match our 11KV system.

We then had several new plants built, this time 433V and our genius engineer decided they should have the correct rotation.

Alterations to one of the older plants threw up a dilemma as we were using 433V but the 550V would remain. Should we reverse it to match the rest of the plant? We decided to reverse the rotation. Every thing was fine until I installed a new switch board that could be fed from two plants. The two incomers did look weird, one RYB the other BYR. By then we had a new engineer, he took one look at my handiwork and wasn't happy. He didn't know about the reversal on the different plants. He still didn't seem convinced when I phased out the incomers in front of him.

The next major plant alteration things got even better 550V BYR 433V RYB.

Become an engineer, confuse the world!

We had two UPS' feeding different panels and each UPS had different phase rotation...one with and one counter to the main switchboard. The issue was "sorted out" at the auto static transfer switch.

The previous engineer had not even made sure that the electricians had colored the phases. When the electricians under me opened the ATS (prior to removal for a new single UPS and maintenance bypass cabinet) we just kind of stared at about 50 black cables and no labeling...whatsoever.

Luckily we had scheduled a complete power outage and were able to identify all conductors offline.

They have colored tapes now and all of the rotations match. Silly me...I think the tinkertoy approach is just easier.

Change two phases on the incoming to correct phase rotation for all machines, then simply leave it alone......

Otherwise, you need to change two phases on each and every machine and in a few years time when the next new idea comes in, you will be doing it all over again, and again, and again.....

K.I.S.S.

To my mind, phase rotation is set by the generators, and from then on is a matter of colour coding of distribution cables and connection to equipment.

Problems do arise sometimes when trying to maintain colour coding integrity, as I recall from an early experience, when a 3-phase 4-wire 415vac underground cable was installed to extend an existing cable to a new swithroom. The cable was laid, cable tiles were laid, and the trench was back-filled.

In those days cable-jointing was a specialised skill (perhaps it still is) and when they turned up they found the colour rotation of the ends of each cable did not match. Apparently the new cable should have been pulled off the drum and laid in the trench from the opposite direction....oops!

The jointers said we would have to re-install the cable, or they would ignore the colours for the joint, and we would have to colour tape the other end. After much argument it was decided the cable colours had to be maintained and the jointers were asked to 'cross' the Bk & Y conductors in the joint box. Which they did - under protest.

In this case the supply phase rotation was RYB. I have never come across a situation where phase rotation was not RYB

I always feel that too much is made about color coding of cables....and then the slightest error, as with the cable layingin a recent post here, and all hell breaks loose......by the way, what difference does it make as to which "direction" a cable is laid...surely the ends will (should) be marked with the same color for the same conductor? Or am I missing something important here?

It is maybe NICE to have it right, but the best idea is to remark the cable ends to make everything look and work as it should and then forget it.

But thats just me I guess......always looking for easy way out.....

I was only an on-looker at the time...an apprentice on the toe of the learning curve.

My recollection of the issue, and the solution, was a 'mistake' had been made and the way to cover it up was to bury it (quite literally). It would have been quite obvious to everybody that something was wrong if cable ends in the new switchroom were taped up with different colours.

The best idea is to use cables with single colours and mark the ends to suit.