On Tuesday, January 12, 2016 at 12:57:36 PM UTC-5, 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?

So, I was at the factory today to fix something completely unrelated, but I threw the phase detector in my toolbag just for the hell of it. Having taken care of today's issues, I spent some time with the maintenance mechanic talking about their three-phase issues. It turns out (as it usually does) to be more complicated than originally stated:

There are about a dozen different machines that plug into a dozen or so outlets, in various combinations. I tested four outlets and found two wired clockwise and two wired counterclockwise.

The plan is to go to all the department heads and compile a list of all the equipment that plugs into three-phase power. We will check each outlet and modify as necessary to get them all running clockwise. Then we'll modify the wiring in the machines as necessary to get them all to run correctly on clockwise power.

This will all end up being a couple of solid days of work, but when it's done, it will be done. Forever. Until someone changes something...

But it was good today to see that the little $20 meter gave good, believable readings.