3 phase rotation direction?

I don't know that they have ever been all that cheap - the volume market isn't really there to bring the price down. 3-phase implies industrial implies prices tend to be rather stiff. I used to put them in as part of our vacuum pump controls (wired in, not a plug in unit), but they were special-ordered and several hundred bucks when several hundred bucks went a bit further than these days.

I see one for $23 that you'd have to wire the plug to (phase indicator, google shopping, not hard to find) - can't be left plugged in (1 hour limit at 200V, 4 minutes at 480 - I guess they use cheap resistors to make a cheap meter)

Step up to ~$80 and you can get a perhaps somewhat better built extech

You won't find one at the Borg, since they don't carry anything three phase. You will find them at most any real electrical supply house for ~$100 or so. The good thing is that those phase rotation meters usually also include motor test functionality so you can identify the leads from an unpowered three phase motor as long as you can manually turn it more than half a turn.

Lots to check out here. Thank you, Google-Fu Master.

--Winston

Yup. I saw the 10 W resistors in some designs, so the temptation to 'cheap out' would be great.

Thanks!

--Winston

It helps to know the proper nomenclature. Good info. Thanks!

--Winston

One additional note is that there aren't too many three phase loads you'll run across that will be harmed by running reverse rotation for a couple seconds, so most of the time you can just blip the load on and see if it's running the correct direction, and if it isn't swap two phases before trying again.

Don't try that if there's an impeller threaded on a shaft. If possible, I had motors decoupled from loads before doing that. Wasn't always possible.

Pete Keillor

I've not seen anything threaded on like that without some additional locking provision, like a slipped in key and locknut. Certainly it is a requirement to look over the device in question to determine what effect a couple seconds of reverse rotation will actually have.

Threaded was standard for a lot of centrifugal pump impellers, no key or nut. We were warned about that when being trained in r&d in the chemical industry. If you checked rotation with the coupling connected you had an even chance of having the impeller rattling around loose in the pump housing. Of course, now they wouldn't let a kid fresh out of college anywhere near that type of equipment. Back then (35 yrs ago), we were expected to keep pilot plants running around the clock, even if it meant swapping 3 phase 460v motors, checking fuses, replacing packing, etc. It was more fun back then.

Pete Keillor

Most everything was more fun "back then"... I fondly remember the days when I could get an Ethernet port and IP address for a new machine in a couple hours, not a couple weeks. Heck, back then I could even get a new power drop under the raised floor in a few days, not a month. *sigh*

That is exactly what did.

I laughed a lot when I saw that the rotor was running backwards. It instantly explained much of our problem with water flow.

A true 'head smack' moment.

Thanks again, Pete.

--Winston

I got away with it. (I realize that does not necessarily mean that the decision was wise or safe).

In my defense, inspection of the impeller showed that the pump in question was little more than scrap anyway. It was missing most of a vane and the rest of it was *very badly* corroded and pitted.

The impeller didn't unthread and the 'magic smoke' stayed in the motor. Call me lucky. :)

--Winston

There wasn't a warning in the manufacturer's data sheet about running the pump backwards except to say that it was not expected to perform it's function if run backwards. :)

--Winston

Or being told that there isn't enough power availible to add something rated 208/240 when the three phase breaker box has everything on a single phase to reduce noise.

Winston wrote in rec.crafts.metalworking on Wed, 26 Jan 2011 06:56:08 -0800:

Could you just find a small 3ph motor and use that?

Otherwise known as the engineer's salute.

Pete Keillor

That would be way too easy...

For machine tools usually I just momentarily turn on the coolant pump before going any further.

I represent that comment. :)

--Winston