# motor tripping breaker



## garfield (Jul 30, 2009)

I have 2 new 40 hp 1800 rpm motors on an auger that's used to load a container to a certain weight. (each one has it's own breaker, contactor etc.) When they get close to the weight they start and stop it 2-3 times within a 5-10 second period to get the weight just right. I have new 80 amp ge tey breakers that are tripping 10 times a day. This morning it was 70 degrees here and the equipment had not been used. I had them show me this thinking they were dealing with an overload condition etc. With an unloaded auger and all components cold it tripped. Voltage and amp readings were all good. We normally put in double the hp for a breaker size. (code would permit a 100 I believe) We have never had this happen I am wondering if GE is the culprit? Any thoughts?


----------



## RIVETER (Sep 26, 2009)

Auger...as I understand..."elevator" pump, right?


----------



## Wirenuting (Sep 12, 2010)

Why did you use an 80 amp thermal/mag if you had a starter with o/l's.
I would have gone with the 100 mag. A 40HP is a bear to start/stop so often and so quickly.


----------



## garfield (Jul 30, 2009)

RIVETER said:


> Auger...as I understand..."elevator" pump, right?


No it's a grain auger.


----------



## RIVETER (Sep 26, 2009)

garfield said:


> No it's a grain auger.


Then...still an auger/elevator, right?


----------



## garfield (Jul 30, 2009)

RIVETER said:


> Then...still an auger/elevator, right?


Yes, I see what you mean.


----------



## varmit (Apr 19, 2009)

Bad application. A 40 HP motor should not be started "across the line" more than 3 or 4 times over an hour. The motor plugging (cycling off/on rapidly) will likely destroy the motor, starter, breaker and any other components in the power circuit. This is an application for a VFD with some sort of sensor interface to slow the motor when nearing the cut-off point. The VFD will also function as a soft start to allow more motor starts per hour without fatal damage.


----------



## garfield (Jul 30, 2009)

I had this discussion with them. We also sell motors and they let me know that they'll buy another one if that happens. When I started working for them they had no functioning overloads on the property and new motors in crates ready to install. I talked them into overloads by telling them I couldn't work for them if we didn't install overloads on the motors and interlocks on the equipment . Believe it or not they've come a long way but they're still not gonna buy the vfds


----------



## Wirenuting (Sep 12, 2010)

Are they using the old style reduced voltage starters? 
The type with resister banks? If so look and see if any have begun to warp and bow out during start up. Have the starter door open but stand way back. I've had those look fine and yet during found that during the bow phase, before failure, the breaker would trip.


----------



## garfield (Jul 30, 2009)

Interesting. We are using oversized iec contactors.


----------



## varmit (Apr 19, 2009)

I understand. You can only do what you will be paid for. I have some of these type customers also. Nothing matters to them other than the equipment running at that moment. Of course, they cry and moan when things fail.


----------



## backstay (Feb 3, 2011)

varmit said:


> I understand. You can only do what you will be paid for. I have some of these type customers also. Nothing matters to them other than the equipment running at that moment. Of course, they cry and moan when things fail.


What type of breaker feeds the motors, what voltage and three phase?
80 amp seems really low for a 40 HP of any voltage. More like 150 amps and up.


----------



## oliquir (Jan 13, 2011)

can you make a wye delta starter , it would be easier on motor and overloads but produce a lot less torque on startup


----------



## telsa (May 22, 2015)

The client either breaks down and pays the money for a squared away system...

Or the motor breaks down and the client pays the money for a squared away system.


----------



## MDShunk (Jan 7, 2007)

If you connect your loadcells to a PID batching controller that controls VFD speed, you'll only need to start the motor once per batch fill cycle. You can fill 10's of thousands of pound loads to ounce accuracy with that control scheme.


----------



## garfield (Jul 30, 2009)

MDShunk said:


> If you connect your loadcells to a PID batching controller that controls VFD speed, you'll only need to start the motor once per batch fill cycle. You can fill 10's of thousands of pound loads to ounce accuracy with that control scheme.


They have two different scales that are just normal truck scales from Fairbanks and rice. I guess I would have to talk to them about an output for that? Different trailers and different trucks and different products have different amounts of gross weight needed. They would need to have the ability to kEy in how much weight they wanted in the trailer. Really if the motor starter would kick out when the weight was reached that would be close enough because they just need to be within a couple hundred pounds.


----------



## MDShunk (Jan 7, 2007)

Yeah, you could automate that so easily, and with the accuracy you need, you won't even need a PID loop. Just a batch controller. Oh, and a loadcell output or even a 4-20ma from your truck scale. The hardware you need to do this is off the shelf and has been around forever.


----------



## garfield (Jul 30, 2009)

MDShunk said:


> Yeah, you could automate that so easily, and with the accuracy you need, you won't even need a PID loop. Just a batch controller. Oh, and a loadcell output or even a 4-20ma from your truck scale. The hardware you need to do this is off the shelf and has been around forever.


I am all for the batch controller but I don't know how they are going to enter the weight they want as each one is different. I have no experience with batch controllers. I googled it and it looks like most of them are geared to specific "recipes" versus a different weight every time.

What's the actual output that comes from the scale to the scale readout? I was thinking about just utilizing that signal into a plc then scaling it to the weight like I think the readout does. I was thinking about a touchscreen that you could enter the weight on then scale it to whatever the scale output versus pounds is. It could really run full speed on the motor starter then stop. This would be 5-6 starts per hour instead of the human bumping it a bit at a time and having 20 starts an hour


----------



## Big John (May 23, 2010)

garfield said:


> ...And having 20 starts an hour


 How often have they had to replace that motor? NEMA puts a 40HP motor at a max of 8 starts per hour, those must run wicked hot.

I think you're on the right track trying to reduce the number of starts. I'm not sure reduced-voltage starting would save you anyway, my understanding is the I2R inefficiency that is heating the motor doesn't improve much even when not DOL starting, because what you save in inrush current you lose in accelleration time.


----------



## varmit (Apr 19, 2009)

Most any "modern" industrial scale will have an adjustable gross setting and an output of some sort that will toggle at the setpoint. 

At it's most simple form, the scale contact would be the "stop" of a 3 wire control and a "start" button would start the auger. This logic would probably operate an interposing relay to energize the motor starter.


----------



## telsa (May 22, 2015)

.....


----------



## JRaef (Mar 23, 2009)

Big John said:


> I think you're on the right track trying to reduce the number of starts. I'm not sure reduced-voltage starting would save you anyway, my understanding is the I2R inefficiency that is heating the motor doesn't improve much even when not DOL starting, because what you save in inrush current you lose in accelleration time.


Yes, you're right. RV starting just trades peak current for longer time. The area of the curve representing accelerating energy stays the same, it's just a different shape. There are papers written to support this. VFDs are different because it completely changes the equation, but it's hard to justify the expense of that's the only reason to use it. 



> How often have they had to replace that motor? NEMA puts a 40HP motor at a max of 8 starts per hour, those must run wicked hot.


Actually, the NEMA starts per hour charts are load dependent. We don't know the original selection criteria for that 40HP motor. It could be that the original designer knew it would take 25HP, but because he KNEW it would start more often, he bumped up to 40HP. That's exactly what you need to do it you have a high duty cycle; de-rate the motor. 

The original problem is the breaker tripping. Even if the motor is de-rated for the application because of duty cycle, that can still be problematic for breakers. Did you observe the mag trip settings? The range of adjustment should go to 10x the rating, so 800A max. Your 40HP motor should be around 56A, so code allows up to 1700% if proven to nuisance trip at a lower setting. 800A, the max setting, is only 14x, so you are justified in cranking the mag trip dial all the way up. I'd try that first, it's free.


----------



## RIVETER (Sep 26, 2009)

garfield said:


> Yes, I see what you mean.


Install a soft start.


----------



## ponyboy (Nov 18, 2012)

RIVETER said:


> Install a soft start.



Great contribution pal


Sent from my iPad using Tapatalk


----------



## garfield (Jul 30, 2009)

JRaef said:


> Yes, you're right. RV starting just trades peak current for longer time. The area of the curve representing accelerating energy stays the same, it's just a different shape. There are papers written to support this. VFDs are different because it completely changes the equation, but it's hard to justify the expense of that's the only reason to use it.
> 
> 
> Actually, the NEMA starts per hour charts are load dependent. We don't know the original selection criteria for that 40HP motor. It could be that the original designer knew it would take 25HP, but because he KNEW it would start more often, he bumped up to 40HP. That's exactly what you need to do it you have a high duty cycle; de-rate the motor.
> ...


The original motors were 25 hp but they were running up in the service factor or above depending on the product. I do think that the 25 hp motors were 5-10 years old. I think I'm going to come off of the buss of the 200 amp service and put manual motor protectors in an enclosure ahead of the motor starters for short circuit and overload protection. The current breakers are ge tey thermal magnetic and they are not adjustable. I have my ge rep pricing me the magnetic only breakers but I bet when I get the price I put in manual motor protectors.


----------



## Big John (May 23, 2010)

JRaef said:


> ...VFDs are different because it completely changes the equation...


 I thought the problem still basically existed with VFDs?


> ...It could be that the original designer knew it would take 25HP, but because he KNEW it would start more often, he bumped up to 40HP...


 Good point. I was assuming a true 40 horse load.


----------



## JRaef (Mar 23, 2009)

Big John said:


> I thought the problem still basically existed with VFDs?


 Not in the same way. When starting ATL or with a soft starter, the stator frequency is immediately at 60Hz, but the rotor frequency is lower as it accelerates. This mis-match of the stator and rotor frequency causes more ohmic heating in the windings of the stator and the rotor bars on the rotor, because it is not yet creating torque since the flux is not fully penetrating, so it becomes heat. With a VFD, your stator and rotor frequency are matched from the outset, so less ohmic heating. The harmonics are causing some amount of extra heating, but nowhere near the same scale.


----------

