# Stuck 480v motor?



## Breakfasteatre (Sep 8, 2009)

have you checked for single phasing?


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## Almost Retired (Sep 14, 2021)

the above does sound very likely
it could be the starter not passing through, or the breaker not passing through
or the bucket stab to the mcc bussbar (or in other words supply to the starter/breaker)

if its not the above, check the fan
will it spin easily by hand without the motor connected to it ?
sometimes bad bearings are overlooked


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## 460 Delta (May 9, 2018)

+2 for the single phasing. Time to break out the meter and step out the power until you find the break.


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## JRaef (Mar 23, 2009)

+3 for single phasing, that shaking back and forth without turning is the classic symptom.


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## SWDweller (Dec 9, 2020)

Pulls 60 amp WHERE, each phase? what are the voltages, L-L and L-G

OL's correct and tight?


Jiggles?


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## gpop (May 14, 2018)

people struggle to spot a single phase condition as it simply trips before they have a chance to test all the leads one at a time so take the easy approach and put all 3 leads going to the motor in the amp clamp at the same time. 
Under 1 amp is normal, over 1 is something to think about and over 10 amps on the meter is a dropped leg.


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## MrGus480 (May 25, 2018)

MrGus480 said:


> I've got a 3ph, 480v motor on an AHU that keeps tripping thermal overloads. The odd thing is that it's a brand new motor, we just pulled the old motor out due to these symptoms, thinking it was bad. When I start the unit without the motor hooked up, everything runs normally (with the obvious exception of the motor. When the motor is connected, it pulls 60+ amps (rated for [email protected]), the pulley jiggles back and forth a bit, then the thermals trip. We've even changed the wires because the b phase was slightly damaged. I'm out of ideas.




Update: the motor was wired off of a Siemens contactor using a Schneider LRD21 din mounted thermal overload for protection. We bench tested the motor we removed and it ran normally. We then bypassed the LRD21 and the unit ran normally. Diagnosis: faulty thermals. Found significant evidence of inductive heating upon removal.


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## 460 Delta (May 9, 2018)

MrGus480 said:


> Update: the motor was wired off of a Siemens contactor using a Schneider LRD21 din mounted thermal overload for protection. We bench tested the motor we removed and it ran normally. We then bypassed the LRD21 and the unit ran normally. Diagnosis: faulty thermals. Found significant evidence of inductive heating upon removal.


A bad IEC overload, who would have guessed, so much for that European quality that’s supposedly equal to NEMA.


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## mburtis (Sep 1, 2018)

I've had to replace a couple Schneider electronic overloads. They would trip well below the setting. The adjustability is nice but I'm not sure I'm sold on electronic overloads.


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## kb1jb1 (Nov 11, 2017)

460 Delta said:


> A bad IEC overload, who would have guessed, so much for that European quality that’s supposedly equal to NEMA.


I am not a fan of the IEC contactors either. They do not seem as robust as NEMA.


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## gpop (May 14, 2018)

MrGus480 said:


> Update: the motor was wired off of a Siemens contactor using a Schneider LRD21 din mounted thermal overload for protection. We bench tested the motor we removed and it ran normally. We then bypassed the LRD21 and the unit ran normally. Diagnosis: faulty thermals. Found significant evidence of inductive heating upon removal.



Use the force luke ..... Sorry i meant use the meter mate. 

Dropped phase 30 seconds with a amp clamp. Locating the problem 60 seconds with a ohm meter. 
Bench testing and bypassing a suspected problem at 480v can earn you a quick trip to the burns center unless you installed a lot of safety's. 

E.g bypassed the overloads motor had a open phase which lead to a fire as the overloads were bypassed and the disconnect did not like opening a single phased motor.


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## 460 Delta (May 9, 2018)

mburtis said:


> I've had to replace a couple Schneider electronic overloads. They would trip well below the setting. The adjustability is nice but I'm not sure I'm sold on electronic overloads.


The Siemens/Furnas ESP-200 on the NEMA line is pretty nice and robust with usable features like phase loss, phase imbalance, ground fault, and selectable trip rate of 5 through 30. The dial adjustment does make me a trifle nervous with some guys in ops, but I have learned to let it go.


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## CAUSA (Apr 3, 2013)

NEMA or IEC I like both as long as they are properly sized and installed.

found this the other day on a unrelated call out.


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## Breakfasteatre (Sep 8, 2009)

Up here in Canada, in industrial for the last 8 years, I have not seen a Nema contactor in a panel in a long ass time. I got a service call to replace the overload heaters a couple years ago but I couldn't find anyone who had the replacements in stock and I didn't end up going


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## MrGus480 (May 25, 2018)

gpop said:


> Use the force luke ..... Sorry i meant use the meter mate.
> 
> Dropped phase 30 seconds with a amp clamp. Locating the problem 60 seconds with a ohm meter.
> Bench testing and bypassing a suspected problem at 480v can earn you a quick trip to the burns center unless you installed a lot of safety's.
> ...



By the time I decided to bench test the "old" motor, both had been resistance tested and we'd eliminated a bad motor as the fault. I'm a licensed master, I just don't have as much time in the industrial world as I'd like but I'm not an idiot when it comes to troubleshooting.


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## JRaef (Mar 23, 2009)

mburtis said:


> I've had to replace a couple Schneider electronic overloads. They would trip well below the setting. The adjustability is nice but I'm not sure I'm sold on electronic overloads.


Just so you know;
Most SSOLs detect a phase loss by looking for there being less than 20% current on any one phase (and all 3 phases qualifies of course). It's a very reliable way of detecting it because if you lose a phase when the motor is running, the motor will generate a voltage on the dead phase that can fool voltage based phase loss detectors into thinking everything is fine. If however those were the "MotorLogic" versions, Schneider / Sq. D had a problem with those SSOLs on pump panels because if the motor was not pulling at least *30%* of the rating of the device, as was often the case if a pump had low flow, it would falsely trip on Phase Loss and there was no way to defeat it. They later released a "special pump panel version" of that MotorLogic SSOL that gave you the ability to turn off the Phase Loss, but you had to know that it existed in order to order it, and distributors rarely stocked it (or even knew about it). But why Sq. D chose 30% is beyond me, that was a major faux pas.


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## JRaef (Mar 23, 2009)

CAUSA said:


> NEMA or IEC I like both as long as they are properly sized and installed.
> 
> found this the other day on a unrelated call out.
> <photo clipped>


LOL, that might as well have been a piece of wire!


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## JRaef (Mar 23, 2009)

460 Delta said:


> The Siemens/Furnas ESP-200 on the NEMA line is pretty nice and robust with usable features like phase loss, phase imbalance, ground fault, and selectable trip rate of 5 through 30. The dial adjustment does make me a trifle nervous with some guys in ops, but I have learned to let it go.


Put a dollop of Torque Seal on it after you set the dial. It doesn't stop a determined idiot, but at least you know when they tweak it because it dries hard enough to have to break it to move the dial.


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## gpop (May 14, 2018)

MrGus480 said:


> By the time I decided to bench test the "old" motor, both had been resistance tested and we'd eliminated a bad motor as the fault. I'm a licensed master, I just don't have as much time in the industrial world as I'd like but I'm not an idiot when it comes to troubleshooting.


No ones called you a idiot but you do lack industrial experience so in hind-sight would you take the same approach. Luckily the motor survived multiple single phase starts so its all good. 
You can either learn to use your meter to find the problem or earn a reputation as a parts changer. 

On a side note only a few people on this site have the ability and equipment to diagnose a good motor the rest of us can only diagnose a bad one. (im not one of them either)


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## backstay (Feb 3, 2011)

I can’t think of anything easier to troubleshoot than a 3 phase motor. A wiggy, clamp on amp meter and a megger is all you need for the basic kit.


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## just the cowboy (Sep 4, 2013)

460 Delta said:


> The dial adjustment does make me a trifle nervous with some guys in ops.


We would use a drop of clear nail polish to make them stop from moving it. Nail polish was just enough to make it not move easy so they did not want to break it thinking it was locked somehow, but we knew we could move it if needed also showed if they moved it by breaking the drop. Same with trim pot adjustments.

OOPS did not see @JRaef post #19. Great minds think alike


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