# Just a general single phasing question



## Noble 32 (Feb 25, 2013)

First some history. About 2 months ago we had several contractors come in for an expansion in a department. Of course we spec powerflex and level 3 safety controls and we get no name cheapest drives and level 1 safety controls. 
Speed up 2 months and my boss is asking to reroute conduit and replace the plastic already broken by production disconnects with nice pretty stainless 60 amp eatons that we keep in stock. Do all that rerunning some wiring and controls and bam done. Before I personally say hey I am done I get my boss and we run through everything to make sure it is kosher working properly. almost 2 weeks to the day I get a call out to that machine because "it just stopped running". Go into the control box starter is pulled it, e stop circuit is not tripped, starter starts and stops with the button.

I go look at the motor and it is hot enough to cook eggs on. turn off disconnect and lo and behold a wire has come out of line side of it the terminal is as loose as it can be with out falling out. I reseat the wire tighten it and every screw in there. Turn it back on and let it roll. No problems.

My question is this, is it possible for the motor to have been single phasing yet running perfectly normal for the last two weeks or is this a case of someone wanting and extra 15 minutes break while maintenance fixes their machine? To me the answer is a huge no but I am curious if it is possible that I didn't tighten that lug when I installed and t just worked its way out.


----------



## oliquir (Jan 13, 2011)

even if not torqued, the wire could have make a good contact enough to keep motor running for few days, then with vibration or heat/cool cycle wire has moved


----------



## Noble 32 (Feb 25, 2013)

I mean I have worked on single phased motors before and they rarely lasted more than a few hours. The only load this motor had was about 13-15 3 lbs chickens and a 50:1 hub city gear box. The wire I reseated was completely removed from the disconnect body. Like ti was undone and pulled out.

Normally this wouldn't be a big deal to me but the company has been cracking down on maintenance to the point when I replace a motor I have to fill out paper work with 20 items on it I have to test before I can put a new motor on. When it takes 30 mins to do all these test and we are getting hollered at by production about down time it kinda gets old fast


----------



## mikey383 (May 21, 2012)

Was it possible the motor was running, then stopped?

If a 3 phase motor is started, then one of the phases is lost, it will continue to run until brought to a stop. Once it's stopped, it won't start again until it has all 3 phases.


----------



## tates1882 (Sep 3, 2010)

Noble 32 said:


> I mean I have worked on single phased motors before and they rarely lasted more than a few hours. The only load this motor had was about 13-15 3 lbs chickens and a 50:1 hub city gear box. The wire I reseated was completely removed from the disconnect body. Like ti was undone and pulled out. Normally this wouldn't be a big deal to me but the company has been cracking down on maintenance to the point when I replace a motor I have to fill out paper work with 20 items on it I have to test before I can put a new motor on. When it takes 30 mins to do all these test and we are getting hollered at by production about down time it kinda gets old fast


 well I doubt it was single phasing for two weeks. More like there was finally enough resistance or vibration to open the connection. Was the ol tripped? If in doubt take a megger to it. If that motor was single phased for any real length of time you'll see a drastic difference in one of the three windings on the megger.


----------



## Southeast Power (Jan 18, 2009)

Could the machine push the motor. It is possible that a production worker could push start the line from the other side of the reduction gearbox?


----------



## JW Splicer (Mar 15, 2014)

Wrap a bunch of tape on the wire nuts... You can find the culprit by looking at the black goo on their fingers!


----------



## Noble 32 (Feb 25, 2013)

The motor regenerating is feasible. The call was the line was running and just stopped. No tripped overloads.


----------



## JRaef (Mar 23, 2009)

I smell a rat...

As mikey383 said, a 3 phase motor will not start if one phase is missing, there is no relative direction of rotation, it just locks up and vibrates. So the wire would have needed to come off AFTER it was already running. If that were the case, you would see clear evidence of arcing and sparking on the terminal because as the wire moved away under load, it would have drawn an arc and burned the terminal and the wire. If the terminal is clean, that didn't happen.

Which leaves either the situation jrannis mentioned, that ANOTHER motor on the same conveyor, or the LOAD on that conveyor going down hill, caused that motor to start rotating on it's own, and THEN because there was single phase power on it, it kept moving. If the load was light enough on the motor, it would not trip the OL relay so it could have done that forever.

The thing that doesn't fit is the sequence. You say they told you it JUST STOPPED, but then you said the OL relay was not tripped, right? Nope, not going to happen. If the motor started rotating for some other reason, why did it "just stop"? Then if the wire just fell out and began arcing, then burned back enough to stop the arc, the motor would still run, but the only thing that would stop it then would be the OL relay tripping. So in either unlikely scenario, the only thing left is someone turning off the starter, then turning it back on, in which case the motor would not restart if single phased. 

So if the OL was not tripped, that ONLY leaves that scenario, which means someone stopped it on purpose, THEN the wire "fell out", then they re-started it, but claimed that it just stopped on it's own. That, to my mind, is someone wanting a break.

I worked for a short time at a brewery where they were forced to hire more people than they needed (or pay the taxes they were forgiven for building the brewery). So there were bored people all over that plant who would get paid whether the bottling line was running or not, but it made a racket. So they jammed it up all the time just to be able to goof off without the noise and still get paid. They were VERY inventive about how they caused jams and shutdowns, it was like a game.


----------



## Noble 32 (Feb 25, 2013)

That is how it is here. I have watched them intentionally hang a line some they can take an extra 15 minute lunch. The oops it just stopped leads me to believe this is the most plausible outcome. There was no arcing nor was the wire blackend


----------



## Jhellwig (Jun 18, 2014)

I would be looking at why the oveloads didn't trip. Unless the motor is way over kill and was running lightly loaded it should have tripped the overloads. 

While 3 phase motors usualy wont start on the own when single phased it doesn't take much to start the. There can be an ever so small amout of kinetic energy stored up somewhere that will help it start. I have seen conveyors take off and run slowly until all the drive line loads up the reverse direction and unload everything till it loads up again.

Don't ever give people the benefit of doubt. They might not be doing it on purpose but they might dumb enough to cause it.


----------



## Noble 32 (Feb 25, 2013)

It is very lightly loaded. I verified the overloads were set right. It is a 1 hp Stirling motor with a 50:1 hub city gear box. Holds maybe 8-12 2-3 lbs chickens at a time


----------



## Guntrician (Jun 20, 2012)

I wish I had a dime for every time I heard "it just stopped" from production workers. Some are honest and very helpful at getting to the accurate diagnosis of a problem. Many others live to throw rocks in your road and want you to be unsuccessful in fixing the problem. All good points above. 

I've seen 3 phase motors run with a phase loose enough to easily fall out but have good enough contact to function. I'd lean towards the "loose lug on install, wire finally falls out, then can't restart after stopping" scenario but like JRaef suggested, there should be evidence of phase loss under load. Some odd things in this one. Weird.


----------

