Motor rotation

sparkie

Lifetime Supporting Member
S
Join Date
Nov 2014
Location
KS
Posts
1,148
So I just converted an entire 480 starter cabinet (had about 10 motors in it) to VFDs and set up the PLC control cabinet for start/stops. Don't you just love it when you put the fuses in and shoot sparks for (seemingly) no apparent reason?

We still never found out what happened, even upon close inspection, but the good news is after a 75 hour week due to some hardcore troubleshooting on my part, the line is back up and running and ready for our conveyor retrofit.

It was also a ton of fun swapping rotation on all those motors but one. At least now we have everything running on standard plant rotation to the disconnects.

Sometimes you just have to chase those gremlins away with a shotgun.
 
What, you got one of the motor directions right first try? How did you do that? That's the second law of three phase motors: if you hook up a three phase motor to an electrical supply, it will run backwards!
 
ASF said:
What, you got one of the motor directions right first try? How did you do that? That's the second law of three phase motors: if you hook up a three phase motor to an electrical supply, it will run backwards!
Click to expand...

robo77 said:
The odds say 50/50, but I say more like 70/30 wrong in favor.
Click to expand...
nope I am more like 80/20 right believe it or not. lol
 
if that worked I'd already have won the lottery haha. But for giggles:
9 17 20 26 31 40
good luck. lol

the real Interesting part is that when I was working with big electric submersible pumps on oil/produced water wells you have to rotate them both ways to.prove which direction is the right one. the wrong one had low ampere an didn't product as soon as predicted or as hard... first one I got right then I got th next 3 wrong. but on purpose. haha
 
Last edited:
Chances are those numbers are better for here anyways as our main lottery is 6 numbers 1-49. lol
 
Has nobody here ever heard of a phase & motor rotation tester
they make getting the correct rotation much quicker, if you use the when you wire up the motor you will get it right the first time every time.
 
ASF said:
What, you got one of the motor directions right first try? How did you do that? That's the second law of three phase motors: if you hook up a three phase motor to an electrical supply, it will run backwards!
Click to expand...

sparkie said:
(had about 10 motors in it)
Click to expand...


You forgot the last part of the law:
If you hook up a three phase motor to an electrical supply, it will run backwards, 9 out of 10 times. :eek:
 
Well, that's the optimistic version.

I once had a setup where we'd wired 10 identical motors. We wired them all the same way, to the same panel with the same phase rotation. I checked the first three and they all went the wrong way. Figuring everything was identical, I isolated the board and changed all 10 motors. Powered back up, and now the 3 that I'd checked all went the right way, and...

The other 7 all went the wrong way o_Oo_Oo_O
 
Do you think maybe the motor winding shops just have fun numbering the motor leads whatever way they choose at that moment?

Just another conspiracy theory in the works.
 
I had a similar problem several years ago. We bought some used equipment from another plant. Every motor in the equipment was backwards. Not a big problem right? Just test it make sure it is just like all the other motors - backwards. Swap two wires and you are done. However the electrician I had do the work missed a couple. The one that comes to mind is a vacuum system. It worked but for some reason it ran hot. Years after that electrician left the bearings on that vacuum fan needed to be replaced. The mechanic turned the power on to demonstrate that he fixed it and I said "Is that going backwards?" Yep
 

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