A new one on me

[petersonra]

I went to start up a project today. I could not get a motor to turn over. I thought the VFD was bad. It was an overhead crane project for a wash line and the traversing motor would not turn over. At first I thought it was the brake but turned out the brake was fine. And I thought maybe I had misconfigured the drive somehow. But no, it turned out to be okay too.

Then the maintenance guy started playing with it when I started up the drive. It would just hum out at the motor a little bit until he gave it a push. Then it would run fine. Even stranger it did not seem to matter which direction he pushed it. The motor would take off in that direction once he got it moving. Eventually we found a loose wire on the motor terminal block and once all three wires were tight on the terminal block it worked fine. Never had that happen before.

 

[augie47]

I've experienced that on a 3 phase motor that had single phased (lost one leg) but was not on a VFD.
It was on a fan and the maintenance guys would turn it on and spin the blade before the OLs opened.

 

[winnie]

IIt would just hum out at the motor a little bit until he gave it a push. Then it would run fine. Even stranger it did not seem to matter which direction he pushed it. The motor would take off in that direction once he got it moving. Eventually we found a loose wire on the motor terminal block and once all three wires were tight on the terminal block it worked fine. Never had that happen before.

The motor sitting until it gets pushed and then going whichever way it has been pushed is a classic symptom of single phasing.

Jon

 

[petersonra]

The motor sitting until it gets pushed and then going whichever way it has been pushed is a classic symptom of single phasing.

Jon

I figured that after a while. Just never had it happen to me before.

 

[hillbilly1]

Same thing with single phase motors with blown start capacitors.

 

[Eddie702]

3 phase motor will run on single phase once it gets going but will drop RPM and increase amps probably overheat

 

[Jpflex]

I've experienced that on a 3 phase motor that had single phased (lost one leg) but was not on a VFD.
It was on a fan and the maintenance guys would turn it on and spin the blade before the OLs opened.

Yes indeed, we come across this scenario at lot at work since we work on numerous 3 phase motors

 

[petersonra]

Yes indeed, we come across this scenario at lot at work since we work on numerous 3 phase motors

You must have a lot of loose wires.

 

[Frank DuVal]

Or a lot of fuse protected motors where one fuse blows, the most common reason. Breaker protected motors do not exhibit this (common trip breaker of course).