Motor overload setting 9

[katwalatapan]

Hello,

The existing motor is 3-phase, 208V, 3.82A FLA. It is controlled via an Eaton motor starter rated for 18A and an overload setting of 4.56A. The motor is damaged and as a stop gap measure, an available 1-phase, 208V, 5.68A FLA motor could be installed. I've confirmed with the manufacturer that the exisiting motor starter and overload could be re-used for 1-phase motor, however the max setting of the existing motor overload is 5.23A.

Could the existing motor starter and overload be re-used for this application. I understand, that the max. overload setting should be 125% of the motor FLA, but in this case the max. overload setting is less than the motor FLA. To avoid any starting or overload issues, would it be best to install a new motor starter and overload with higher amperage setting? OR could the existing overload max. setting be acceptable?

I'd appreciate your comments on the above.

Thank you.

 

[ScottyUK]

Try it and see. If your motor is loaded to maximum capability then it might trip, if not then it will probably work OK. You should wire the three overload elements in series for single phase duty.

 

[Parchie]

@katwalatapan,
Your original motor is rated 3/4 HP (3.2A, 208V, three-phase) and you are going to replace it with a smaller capacity 1/2 HP (5.56A, 208V, single-phase).! Assuming both motors have the same full-load speeds, if the motor actual load is really around 3/4 HP, you'll overload your 1/2 HP for sure. IDK if you could change pulley sheeve or what, so you can make use of that single-phase motor.

 

[jraef]

You can set an OL relay for any value you like that is under the FLA, the issue is the load on the motor. If the load requires more current than the setting allows, it trips. If not, you're OK. I would hazard a guess that you are going to get nuisance tripping.

By the way, you assumption about the 125% is likely what killed your old motor. The Eaton OL relay has ALREADY factored in the 125% in the pick-up point of the OL trip curve, so by you adding an ADDITIONAL 25%, your OL was not even beginning to count down until the current reached 156% of the motor FLA!

Common mistake. You assumed that the NEC allowance is an instruction sheet, but that's not the case. It is a MAXIMUM in order to prevent fires. Setting of OL protection is done by a process called "RTFM"; Read The "Factory" Manual. The manual for that OL relay would have told you to set it for 100% of the FLA.

(The F usually doesn't mean Factory in the more vernacular version)


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[waross]

The Eaton OL relay has ALREADY factored in the 125% in the pick-up point of the OL trip curve, so by you adding an ADDITIONAL 25%, your OL was not even beginning to count down until the current reached 156% of the motor FLA!

Common mistake. You assumed that the NEC allowance is an instruction sheet, but that's not the case. It is a MAXIMUM in order to prevent fires. Setting of OL protection is done by a process called "RTFM"; Read The "Factory" Manual. The manual for that OL relay would have told you to set it for 100% of the FLA.

I have installed many overload devices that required you to add a safety factor of up to 125%.
I have also installed many overload devices that had the factor built in and were set at the motor FLA.
This takes us back to RTFM. You can't guess. For proper protection and avoidance of nuisance tripping you must "READ THE FLIPPIN' MANUAL".

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[katwalatapan]

Thank you very much for all the response.

 

[iceworm]

By the way, you assumption about the 125% is likely what killed your old motor

katwalatapan -
I don't know how jraef knew that likely was the cause of the motor failure. I didn't see anything in your post that even alluded to that being the cause. And anyway, even if the overloads were inadvertantly set too high - that is not what damaged the motor. The motor was damaged by poor design resulting in overload, bad bearings, poor operator control allowing process to overload, coil winding shorted, something else of these natures. The best the overloads can do is shut off the motor when there is a failure, before it catches fire, and maybe catch dragging bearings before the windings get taken out. The overloads don't come into play until something broke.

Some think motor overload can be cured by changing the overload setting. That seems to be a "common" mistake. However, You can't. The motor load is set by design. Setting the overload up or down won't change that. So, if the motor burned up because it was overloaded, fix the design - cause setting the overloads down don't fix a thing.

Yes, you do have to read the particular manual for the overloads. And my recomendation is to also check the running current right at first commissioning. If the design is crowding the motor loading - then fix that. There is no reason to be afraid of setting up the overloads - where ever they need to be. They are a protective relay, not a process control.

Curiousity questions:
Q1: As you said, the motor is 208V. That is a bit odd, most motors for 208V systems are 200V nameplate. However, sometimes motors are 208V - 230V nameplate. Is this what you have?

Q2: 208V system, likely 60Hz. Is this a NEMA motor? If so what is the sf?

I ask because these will matter if the loading is crowding the motor. And if they are IEC motors, that will matter as well

Overload philosophy per
The Worm

Harmless flakes working together can unleash an avalanche of destruction

 

[waross]

I see both 200 Volt rated motors and 208 Volt rated motors.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

While I agree the improper setting of the OL relay didn't cause the overload, if there was an overload, the improper setting allows the motor to be damaged before it acts. If the OL relay is set properly, AND something in the load causes a temporary overload condition, the OL relay trips and saves everyone a lot of headaches while you investigate the cause of the overloading condition. By the time an OL set to not pick up until current gets to 156% of FLA before it even begins to take action, the windings are going to be damaged by the time it finally trips.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[iceworm]

Interesting - post went away. maybe someone is telling me to try a different tact. okay
Glad to see you understand the overload setting did not cause an overload.

You can set an OL relay for any value you like that is under the FLA, the issue is the load on the motor

And this one is just wrong. Contains assumptions that are not in evidence concerning the ability of the one doing the settings to calculate the actual setting.

By the time an OL set to not pick up until current gets to 156% of FLA before it even begins to take action[/jraef]
This and several other comments contain assumptions that the op mis set the OL. There is no evidence in the op this is true.

If the OL relay is set properly, AND something in the load causes a temporary overload condition, the OL relay trips and saves everyone a lot of headaches while you investigate the cause of the overloading condition

We have different philosophy concerning the purpose of an overload relay.
To my thinking, the primary purpose, in the event of a failure that overloads the motor, is to shut off the motor before it catches fire. If the failure is internal to the motor, there is no motor to save - it failed. If the failure is external to the motor, then the secondary purpose is to save the motor. And sometimes that happens - and that is good when it does.

Got to go to work - got someone paying my time. later

ice

Harmless flakes working together can unleash an avalanche of destruction

 

[Parchie]

ice,
While you downplay TOL function as merely a fire protection requirement, most in the manufacturing industry see it as a "profit/loss" item! When motor thermal protections are set to closely mimic the motor thermal capability, you'll prevent motor burnouts-->lesser rewinding/dismounting/installation costs. Why design for destruction by fire, when you can save the equipment?

 

[iceworm]

Parchie -
You certainly have some excellent points. However, I don't think I am down playing the importance of motor overload protective functions.

When you say "most in the manufacturing industry see it as a "profit/loss" item", I'm curious as to exactly which industries. Cause, I don't see that much, especially for smaller motors - say under 200 hp.

Caution {rant-on} suggest burn before reading
I've been involved in Oil and Gas refinery and pipeline, petroleum bulk plants, pulp industry for around 50 years (welders helper, 1965). Engineering since 1973. The majority of my clients (not so much for bulk plants) are concerned with high reliability, running flat out, 24/7. They would insist on 365 days per year, if maintenance shutdowns weren't mandatory. Starting from that mindset, the concept of a dead fractional horse power motor showing up on the P/L statement is completely alien. Now consider that some processes are conceptually a series string of 50 pumps/motors with maybe as many valve actuators. One miserable 3/4hp motor can take down the whole process. Common practice is to have install spare pumps/motors for every critical piece, yep, right up to multi-thousand horsepower.

Considering this mindset, is it suprising that unless specials are involved, fractional horsepower may not be repaired at all, under 10hp may not be considered for rewind. Generally there is no squawking if a motor trips on OL. Things do break - manmade, it will break - that is a fact. However, generally, if the customer could remember the last time, they are telling me they want to investigate increasing the reliability.

Consider the customers are not whining about the motor costs, rather they are majorly whiny about the downtime to repair. Okay, you say, keep the overloads set down and they won't burn up and require replacement. Possibly. Maybe in the world of IEC motors, it is necessary to design for 90% loading and set the overloads at 100%. I couldn't tell you - no experience. Nema motors, the design will be as close to 100% loading as possible. Most clients will opt for 1.15sf to increase MTBF. And the OLs will be set 125% - 140%. And truely, I've never had a motor burn up (winding failure) because the overloads were set up to NEC max. They burn up because:
[ul]
[li]The windings shook a hole in the insulation;[/li]
[li]5 years of high ambient, heavy load, 24/7 finally took its toll. When one considers that is close to 50Khrs - that's not bad;[/li]
[li]Bearings failed and put the rotor into the stator;[/li]
[li]Cleanup crew using a fire hose (pulp mill - amazing how much water one can get past the shaft on a TEFC with a fire hose);[/li]
[li]Operators can adjust process to overload motor and trip. Reset repeatedly until the smoke comes out. (Pulp Mill - wood room) OLs with thermal model not commonly available.[/li]
[li]HVAC air handler designers spec/buy 1.0SF 208-230 motors, load them right to 100%, locate in high ambient areas, and then are suprised when they burn up frequently. Fortunately this one is easily fixed. Replace with 200V, 1.15sf motor - often same footprint, just twice the money. Yes, on 208V systems, heavily loaded 208-230V motors run hotter than 200V motors. Twice the money pales next to repair/replace every few years[/li]
[li]And one that maybe could have been saved by overloads. Definitely could have been saved by a modern electronic overload/motor protection relay. 4160V, 900hp, 900rpm to a hydraulic speed reducer, driving an ID fan. Fused contactor, no overloads, operator set the load by adjusting the speed reducer output RPM, relying on a winding RTD readout. One fuse opened, motor single-phased for maybe 30 seconds. Ruined it beyond rewindable. Don't know why the fuse opened. Electronic motor protection not commonly available - not uncommonly available either. We put in a phase loss relay. Don't know why they did not have one before.[/li]
[/ul]

So where am I headed:
[ul]
[li]Yes, saving the motor or limiting the damage to the motor is important.[/li]
[li]Putting out the fire is top of the list. Especially since there may not be a motor to save anyway.[/li]
[li]Fractional hp rarely (like never) make the list of financial concerns.[/li]
[li]Advising to set OL at 100% sounds wrong on so many levels.[/li]
[li]Yes, plenty of us can read.[/li]
[li]Automatic assumption that the OP had not bothered to correctly set the OL and that caused the original motor failure does not sit well.[/li]
[li]Up to a few hundred horsepower, replacing a motor is just a cost of doing business.[/li]
[li]The more expensive the motor, the more extensive the protection (Really? Well thank you Captain Obvious)[/li]
[li]I have not been around any industry where the cost of a fractional horsepower motor could ever possibly matter. The down time will, but not the motor.[/li]
[li]Yes, it is always about the money[/li]
[li]Example: Say you have an installation where a fractional/integral hp motor experiences 3 trips/ year resulting in 1 hour downtime and a plant startup each trip. One sets the overloads up to max and gets no trips for two years, then motor burns up. Takes 10 hours to replace motor, maybe a problem. Takes 1 hour to change a motor - not a problem.[/li]
[li]I highly suspect we live/work in different worlds - and that is okay. We all have to make a living. However, the rules for one likely do not fit the other[/li]
[li]Yes, it is always about the money.[/li]
[/ul]
if you got this far, thanks for listening {/rant-off}

continued overload philosophy per
the worm

Harmless flakes working together can unleash an avalanche of destruction

 

[waross]

Pumping applications are not the only use of industrial motors. Sawmills, rock quarries and gravel pits, conveyor drives and many other applications do not have the perdictable loading of pumps. Overloading motors is more of an issue and most of the folks working in those industries will remember quite a few overloaded motors that were saved by properly set Overload Devices.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[iceworm]

Pumping applications are not the only use of industrial motors. ....

... Sawmills, rock quarries and gravel pits, conveyor drives and many other applications do not have the perdictable loading of pumps. ....

Both of these are true. I don't see how they apply to anything I said.

... Overloading motors is more of an issue ....

I don't agree. The issues in these industries are no worse than the ones I highlihgted..

... most of the folks working in those industries will remember quite a few overloaded motors that were saved by properly set Overload Devices.

I never suggested anything other than "properly setting the overloads". And still don't.

Having been in a few sawmills associated with pulp mills, a prevalent issue is:

Operators can adjust process to overload motor and trip. Reset repeatedly until the smoke comes out. ...

That is a problem in any industry where the operator can adjust the process to overload. And it generally shows up when the management rates performance by the output ton. "Properly set overloads" won't fix this. Improperly set overloads won't fix this. Low set overloads won't fix this. .... .....

From what I hae seen of rock pits and gravel quarries, the same applies here as well. If the operator can get at the process vaialbles, they can take out the motor - no way out of that.

The Fix:
Construct such that the motors are not overloaded by design - if possible. Yes, it is always about the money.
Where the operator can adjust process, consider thermal modeling electronic overlaods
Yes the overloads must be properly set. "Properly set" does not mean that the motor will never fry from overload.
"Properly set" does mean trip inside of the cable damage curve. And for the first and maybe even the second trip per hour, inside of the motor damage curve. No promises after that.
"Properly set"/extent of protective relaying, is different for fractional hp than 200hp. Blanket statements covering both are about silly. Yes, there is no surprise there.
Its okay to actually measure the motor currents during commissioning - even for fractional hp. I'm suprised how rarely that happens. It appears that plenty operate on the principal, "Hey, we set the overloads in spec. It started and stays running. let's move on."

I'll still assert:

And the OLs will be set 125% - 140%. And truely, I've never had a motor burn up (winding failure) because the overloads were set up to NEC max

I don't see any evidence this does not apply equally well the the industries you mentioned.

and still further delving into the philosophy of overloads by:
the worm



Harmless flakes working together can unleash an avalanche of destruction

 

[LionelHutz]

And truely, I've never had a motor burn up (winding failure) because the overloads were set up to NEC max."

Not once in 43 years of work? Companies will be hiring you just for the good mojo you must be spreading.

 

[iceworm]

I agree! I keep telling them I need a good karma bonus. But I can't get anyone to pony-up. Bummer.

Nope I don't recall even one. Of course that mostly means I could always find another cause besides the overloads were set uo to NEC max.

Anecdotal information suggests the most likely cause of premature motor failure is "PM unto death" - cleaning, greasing right at the top, followed by vibration, cheap bearings, followed by mis-application (such as thin tin, 1.0sf, 100% loaded, high end of ambient spec - add 230V-208V nameplate on a 208 system, and they don't last long at all)

Also anecdotal information:
[ul]
[li]The techs like high end American made bearings. As far as I can tell, high end bearings from any country are equally good. Low end bearings from any country are equally poor. Which is not strange, they all use the same machines, just a difference in QC and quality of finish between the high end and low end.[/li]
[li]Get/specify the right grease. One customer was taking the new bearings out of the package, cleaning and repacking with an ngli2 -60F spec grease. Found out that they ordered enough bearings that if they grouped up the orders, they could specify exactly what they wanted for grease. Took an extra four weeks for delivery. Good deal for all.[/li]
[li]Close tolerance balanced rotors/pump shafts/impellors seem to aid longevity. Suggestion from an old millwright/rotating equipment mechanic. Seemed to increase bearing/seal life.[/li]
[li]Careful alignment adds to bearing/seal life. Assisted with specing/buying highend optical alignment equipment/training. Were definitely able to affect a couple of problem children.[/li]
[/ul]
Just random thoughts. But I got someone wanting to pay me and this is not billable time - enjoyable, but not billable.

Later guys and girls

ice

Harmless flakes working together can unleash an avalanche of destruction

 

[flexoprinting]

Last year this bearing tripped a properly set overload, due to the tight space and working by myself i had to replace both bearings on site it took me about four hours and saved the company $$$.
That motor on our largest compressor is still running now thanks to the overload.

Chuck

 

[iceworm]

Last year this bearing tripped a properly set overload,...
That motor on our largest compressor is still running now thanks to the overload ...

That's great. Good job. Excellent choice on overload setting. You are to be commended.

Just curious: Why would you ever consider NOT 'properly set overload'? I certainly would not. That doesn't make much sense.

Back to work for me. This is interesting, but isn't billable.

ice

Harmless flakes working together can unleash an avalanche of destruction

 

[controlsdude]

I know this is an existing plant. But in my line of work, commissioning equipment, if I don't set the overloads correctly (fla name plate motor = overload setting), I will not see all the mechanical mistakes of misalignments or just sloppy mechanical adjustments.

 

[LionelHutz]

Sorry, but saying that the motor being overloaded by the process is what caused it to fail and not the improper overload is just using silly semantics to justify your overload settings. Not having a proper overload or not setting it correctly will both fail to protect the motor, and then the motor will fail.

When your philosophy is to set the overloads so high that they will only prevent a fire then you're obviously only installing the overloads to pacify the electrical code, with no plans to use them for their intended purpose.