On Tuesday, January 12, 2016 at 8:32:56 PM UTC-5, Clare wrote:
On Tue, 12 Jan 2016 09:57:33 -0800 (PST), 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?
Well, if you know which outlets run it backwards it should be pretty
simple. Just switch any two wires. If you want a "simple as a sack of
rocks" test, just grab a small 3 phase motor and lable the wires - use
it as a test motor to determine phase rotation.

Unfortunately, I don't know which outlets are forwards and which are backwards. And while you'd think the customer would have kept track...Dumber than a sack of hammers comes to mind.

There are actually meters for this that have a tiny motor in them to display the direction. I like that, but I've already received the LED thing from Amazon.