They sell phase rotation detectors, like this one:

http://www.amazon.com/Extech-480400-.../dp/B001AGTXY2

On 2016-01-12, rangerssuck wrote:
I'm doing some work in an older factory - MANY electricians have had their hands in this place. They called me today with a problem:

They have a piece of equipment they have been moving from room to room. It has a 3-phase 230V motor (about 1 HP). In some rooms it runs backwards, so they have been swapping wires inside the motor junction box.

They asked me whether I could add a reversing switch, with a lockout to prevent it from switching while it's running. Well, yes I could do that, but why don't they just rewire the outlets so they're all the same?

Well they think that's a great idea. And I should go up there and make sure they do it right.

So, I COULD identify the correct wiring by simply by plugging in the motor and checking for correct rotation, but surely there's a better way? What if this was a big piece of equipment, or something that would do damage if the motor turned the wrong way?

I COULD hook up my oscilloscope (and it always impresses the hell out of them when I pull that out), but is there an even better way? How do "real" electricians identify the phase connections when they can't count on the wire colors?

[just to get back on the off topic]
How would Bernie, Hillary and Donald do it? How would they do it in Oregon?