Overload Class

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philly

Senior Member
I apologize for the amount of questions here recently however I cant help but to learn from the experts here on this forumn. :grin:

This question deals with the different class overloads in a conventional starter. I know the standard for most bi-metal overloads for most applications is a class 20 overload, although others are avaliable upon request.

I am now working with the AB E3+ solid stage relay, and there are several different overload classes avaliable for this relay with just the click of a mouse. So I wanted to get a better understanding of where the different classes were applicable and what effect they have on the protection of the motor.

I understand that a class 20 overload relay is the most common class setting, and that by definition the relay will allow 6x the relay full load setting for 20 seconds. For each of the other classes wheather it be 10, 30, etc... this same 6x current value will be allowed to persist for a time indicated by the class of the relay. I also notice that with this E3 relay, the class setting will also determine how quickly the thermal model of the relay will decay after the motor is running or has been stopped. I believe the higher the class setting, the quicker the thermal model will decay, unless I have it backwards?

So with all that being said, I was wondering where it would be applicable to bump a standard class 20 overload to a class 30. On application I was aware of were for loads that were hard to start such as fans which took a while to get up to speed. There may be others, but the general rule of thumb seems to be for these motors that take long to get up to speed. By implementing a higher class however, are we risking damage to the motor by allowing higher currents to operate for a longer time during steady state condition when the motor is running?

On a somewhat seperate note, I notice that NEC allows overloads to be rated at 125% of FLA for motors that have a 1.15 service factor. It is my understanding that the bi-metal overloads from manufacturers charts already have this 125% built in so when selecting you should select the range that is applicable for the motor full load without any adjustment to the numbers. What about setting these solid state overload relays? If the motor has a 1.15 S.F. should you enter just the FLA assuming the relay accounts for this factor or do you need to adjust this current setting for the S.F.?
 

Jraef

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I apologize for the amount of questions here recently however I cant help but to learn from the experts here on this forumn. :grin:

This question deals with the different class overloads in a conventional starter. I know the standard for most bi-metal overloads for most applications is a class 20 overload, although others are avaliable upon request.

I am now working with the AB E3+ solid stage relay, and there are several different overload classes avaliable for this relay with just the click of a mouse. So I wanted to get a better understanding of where the different classes were applicable and what effect they have on the protection of the motor.

I understand that a class 20 overload relay is the most common class setting, and that by definition the relay will allow 6x the relay full load setting for 20 seconds. For each of the other classes wheather it be 10, 30, etc... this same 6x current value will be allowed to persist for a time indicated by the class of the relay.
That's correct. IN GENERAL, NEMA design motors, i.e. those made for the North American marketplace using NEMA design guidelines, will need Class 20 OLs. IEC motors, i.e. those designed for use in places OTHER than North America, are almost always going to require Class 10 OLs. A lot of Submersible Pump motors, because they are custom built for a specific application, will also require Class 10 OL protection, some even require Class 5. Be careful by the way with IEC motors that are sold in the US by just changing the nameplates to show US voltages and frequencies, because they will still be needing Class 10 protection. A way to possibly tell is if the nameplate shows separate 50 or 60Hz ratings. Class 30 OLs should only be used on special motor applications, commonly referred to as "Mill Duty" motors.

I also notice that with this E3 relay, the class setting will also determine how quickly the thermal model of the relay will decay after the motor is running or has been stopped. I believe the higher the class setting, the quicker the thermal model will decay, unless I have it backwards?
You would have to take that up with A-B. The UL / NEMA Classes have nothing to do with cool down time, only trip time. Some SSOLs have fixed cool-down times, some are variable, some are user programmable.

So with all that being said, I was wondering where it would be applicable to bump a standard class 20 overload to a class 30. On application I was aware of were for loads that were hard to start such as fans which took a while to get up to speed. There may be others, but the general rule of thumb seems to be for these motors that take long to get up to speed. By implementing a higher class however, are we risking damage to the motor by allowing higher currents to operate for a longer time during steady state condition when the motor is running?
Bumping class ratings is a game of chance, the consequence of which can be expensive. Better to bypass the OLR during start and put it back in at the proper class rather than run at the higher class continuously. Most motors, especially NEMA designs, can take short term overloads quite well. That's what the Service Factor is all about. But continuous overloading will destroy the insulation. I once helped design an SSOL where I allowed a 2 stage OL Class to be selected, so for example Class 30 on start-up and once it detected the motor got to speed, drop down to Class 10. I still like that idea (but they no longer pay me to care so I won't give them free advertising). Bypassing the OL is perfectly OK per the NEC if you have proven it won't start without it.

On a somewhat seperate note, I notice that NEC allows overloads to be rated at 125% of FLA for motors that have a 1.15 service factor. It is my understanding that the bi-metal overloads from manufacturers charts already have this 125% built in so when selecting you should select the range that is applicable for the motor full load without any adjustment to the numbers. What about setting these solid state overload relays? If the motor has a 1.15 S.F. should you enter just the FLA assuming the relay accounts for this factor or do you need to adjust this current setting for the S.F.?
Generally, SSOLs are designed around the same criteria as electro-mechanical, including the selection / setting procedures. But even bi-metal OLs are not supposed to be selected to run a motor into the SF unless you absolutely must. The SF is a "fudge factor" meant to allow for temporary shock loads or voltage dips but it is widely acknowledged that running a motor into it continuously will shorten the lifespan.
 
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Cold Fusion

Senior Member
Location
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Philly -
Sounds like you are reading the User Manual. That's good. My responses are based on Pub 193-UM002C-EN-P - 4/04. You may have a later rev.
... I believe the higher the class setting, the quicker the thermal model will decay, unless I have it backwards? ...
Assuming I am translating what you asked correctly, I think you have that backwards. Look at Table 3-3 at the bottom of page 3-6. Using their typical settings, a class 20 will reset in 180sec, a class 30 will reset in 270sec.

... By implementing a higher class however, are we risking damage to the motor by allowing higher currents to operate for a longer time during steady state condition when the motor is running? ...
I don't think so. Three things to consider here.

First, the best protection against overloading a motor to where it will burn up is to design the system to where the motor can handle all normal loads. If the motor is too light duty or too small, you can't fix that by changing the overload class. It the load is high inertia with a long acceleration time then you will need a class 30 or as jraef said cut out the overload on starting.

Second, look at the class 20 and class 30 trip curves, Fig 3.1, page 3-5. For 1000 seconds and up, there is not much difference in the curves. Either overload will trip about the same time on long term overload. The big difference is longer than 100 seconds - when the motor is starting. So, if the motor is consistently experiencing overloads under the class 30 trip curve but over the class 20 curve, then see "Third ....

Third, the motor has to run and drive the customers load. If the motor is consistently running into high overloads, but still under the trip curve you probably neeed to consider "First":roll:. Get a bigger motor that doesn't consistently run up into this region.

... What about setting these solid state overload relays? If the motor has a 1.15 S.F. should you enter just the FLA assuming the relay accounts for this factor or do you need to adjust this current setting for the S.F.?
That's covered on page 3-2 and 3-3, FLA Setting. For sf >= to 1.15, set overload at FLA. For sf < 1.15, set overload to 90% FLA.

cf
 

philly

Senior Member
Assuming I am translating what you asked correctly, I think you have that backwards. Look at Table 3-3 at the bottom of page 3-6. Using their typical settings, a class 20 will reset in 180sec, a class 30 will reset in 270sec.

Okay so since the overload class setting does effect the motor thermal model, should the overload class ever be under consideration for change due to the motor thermal model not recovering quick enough? The way I would see it, is the primary role of the overload is to protect the motor, and in this case the thermal model decay will just have to be a secondary order effect that will have to be dealt with. I guess what I am getting at here, is with a motor for long acceleration times, and that is started frequently sometimes the thermal wont decay quick enough to allow a second start soon after a first start. Should the overload class be considered in this case?

First, the best protection against overloading a motor to where it will burn up is to design the system to where the motor can handle all normal loads. If the motor is too light duty or too small, you can't fix that by changing the overload class. It the load is high inertia with a long acceleration time then you will need a class 30 or as jraef said cut out the overload on starting.

So what you and Jraef are saying, is that it would be better to bypass the overload during a start, however then return the overload to the correct class after motor is started. Can you do this with the E3 modules? By doing this, how would you account for the thermal capacity used up during the starting of the motor? Wouldn't ignoring this during the motor start allow the motor to be started several times not caring what the thermal being used during starting was and possibly damage the motor?

Second, look at the class 20 and class 30 trip curves, Fig 3.1, page 3-5. For 1000 seconds and up, there is not much difference in the curves. Either overload will trip about the same time on long term overload. The big difference is longer than 100 seconds - when the motor is starting. So, if the motor is consistently experiencing overloads under the class 30 trip curve but over the class 20 curve, then see "Third ....

I see what you are referencing. So with that being said, this would lead me to believe that setting to a higher overload class would not have much of an effect on long term running of a motor and would only make a difference during starting. Wouldn't that then be better than simply ignoring the relay during starting? Would there be any risk of long time overload since the two classes are nearly similar for long times?

The particular application that arises these questions for me are for a fan. We are able to start the fan once, but then when we try to start the fan again shortly afterwards relay trips out on an overload. I suspect that the long starting time of the fan is causing the relay to use up a lot of TC during the start, and not decaying that fast thus when we try for a second start we do not have enough TC avaliable to start and thus it trips. What are your opinions for a case like this? Is this a candidate for considering a class change, or just something that should be dealt with due to the nature of the motor and application?
 

Cold Fusion

Senior Member
Location
way north
...The particular application that arises these questions for me are for a fan. We are able to start the fan once, but then when we try to start the fan again shortly afterwards relay trips out on an overload. I suspect that the long starting time of the fan is causing the relay to use up a lot of TC during the start, and not decaying that fast thus when we try for a second start we do not have enough TC avaliable to start and thus it trips. ...
From what you described, that is exactly true. See the part in red, that is alerting you that the operational conditions are damaging the motor. This is a classic design issue.

... What are your opinions for a case like this? ...
(names and places are left out to protect the guilty) So, I'm working as a plant electrical engineer at the Widget Skin Commodity Company. An area foreman reports, "The 100hp motor on the widget skinner is tripping occasionally on overload - go fix it." An electrician and I tie into it. We check the motor nameplate, the overloads, the contactor, all of the connections, bearings, drive mechanism, and the belts - nothing wrong. Overloads are set right up to 140%. We put a recording ammeter on it. Sure enough the crew can overdrive the unit and it trips after a bit. The foreman tells me to set up the overloads. I say no, they are as high as the law allows, and if they trip, reset, and restart more than three times per hour they will likely burn up the motor. It needs a bigger motor. About two days later, I get a call. The motor tripped out three times in the space of an hour and the fourth time they started it, the smoke came out. My response, "Sounds normal to me. I don't see a problem. Everything worked exactly as per design."

... The way I would see it, is the primary role of the overload is to protect the motor, and in this case the thermal model decay will just have to be a secondary order effect that will have to be dealt with. ...
My response may not be a popular view point. The overloads mostly protect the conductors. The overloads keep the motor from catching fire, but they don't necessarily protect it. Oh they might keep the windings from burning up if the bearings go bad, but that is about it.

My story is an excellent example of why not - and yeah, that's exactly the way it happened. The primary motor protection is "good machine design". However, a properly programmed E3+ thermal model can tell you that the motor is undersized. But it damned sure won't fix anything.

This design you are dealing with is poor. Assuming the overloads are set correctly, the motor is too small for the normal load. That's why the overloads are tripping. That can not be fixed by diddling with the class setting or the thermal model.

The overload thermal model is telling you the motor has not cooled off enough to restart with out possibility of damage. As I recall, an AB E3+ allows you to program how soon the thermal overload can be reset. I think you can even set the overload up to where it will reset right away. So, did you set the overload thermal model up correctly? If you did and production management still wants to immediately restart the motor after an overload trip, then my best recomendation is to keep a spare motor handy.

... Is this a candidate for considering a class change, or just something that should be dealt with due to the nature of the motor and application?
This is a canadate to consider for redesign. If the process has to have more fan - get a bigger motor.

Just thought of an option. If this is critical production equipment, say like an ID fan on a boiler, there are other options. The issue here is if the ID fan on a coal fired boiler quits, the FD fan unloads the fire on the boiler room floor - usually into the back pocket of the engineer (as you knew, boiler operators are engineers:))

For something like this, one can install RTDs in the motor, and the operator monitors the winding temperature. The operator adjusts the loading to keep the motor windings below the damage curve.

I've been around a couple of these. It's best to keep a spare motor handy for this type of operation.

So what to do?
Check the E3+ programming real close. Check all of the options. Understand how all of the options interact. Make sure the overload is set right up to the max allowed. My personnal opinion is that setting the overloads down will burn up the motor quicker - more trips, more starts, enough starts per hour and the smoke ... you get it.

Now check the budget. See what you have to spend to fix this. If this motor trips are cutting production you may be able to get all the money you need.

Install monitoring equipment to get a good idea of the motor winding temperature. Maybe the E3+ is set too low and the motor is not getting that hot - probably not, but it could be.

You will need a spare motor soon. Change the purchase spec for the spare. Get the biggest, toughest, severest duty motor that will fit in the hole. With any luck you won't have to change the conductors and the starter - although if you have my luck .. :mad:

You have a good one. let us know how it comes out.

cf
 

philly

Senior Member
CF thanks for sharing your info and experiences.

From what you described, that is exactly true. See the part in red, that is alerting you that the operational conditions are damaging the motor. This is a classic design issue.

So I guess what you are saying is that hands down this is a poor design. For the sake of discussion lets just say that it used 85% thermal capacity on a start. Obviously this would not allow a second consecutive start which most motors should per standards I believe. So seeing that this uses so much thermal on the start are we saying that it is a poor design? Would a better design have been a motor that only used somewhere around 50% thermal on starting?

This design you are dealing with is poor. Assuming the overloads are set correctly, the motor is too small for the normal load. That's why the overloads are tripping. That can not be fixed by diddling with the class setting or the thermal model.

I understand your point of view on this. What about if the motor operates fine once it is up and running, but really only has problems with eating up thermal capacity during starting? Wouldn't a larger overload class help with this? I know section 430.52 of the NEC allows the overload to be shunted during starting, so I would think that a higher class overload would be better than shunting in this case? So where are class 30 overloads used, and on what type of applications?

The overload thermal model is telling you the motor has not cooled off enough to restart with out possibility of damage. As I recall, an AB E3+ allows you to program how soon the thermal overload can be reset. I think you can even set the overload up to where it will reset right away.

I did see this option that you reference in the manual but I wasn't sure what to make of it. My understanding of it was that you would set a point to which the thermal model must decay before allowing the relay to go back to an o.k. condition and allow a restart. But referencing the example I state above, lets say the motor takes 85% to start and we set the overload reset to be when the motor reaches 70%. Even know the overload will clear the thermal overload and allow an attempted restart, we still will most likely be unsucessfull in the restart condisering we do not have enough thermal capacity avaliable. What are your experiences with setting this reset level or where should it be set?

So, did you set the overload thermal model up correctly?

I'm not sure I understand this question. Other then setting the FLA, Overload class, and Overload reset value, what else goes into setting up the thermal model?

Check the E3+ programming real close. Check all of the options. Understand how all of the options interact. Make sure the overload is set right up to the max allowed. My personnal opinion is that setting the overloads down will burn up the motor quicker - more trips, more starts, enough starts per hour and the smoke ... you get it.

Your first post references the instruction manual which states to set the overload to 100% of FLA for 1.15 SF motors, and 90% for non S.F. Your last post then referenced you setting the overloads to 140% when you encountered a problem previously, and I also see that 430.32(C) of the NEC allows a setting of up to 140% for motors with a S.F. of 1.15. What guidelines should be adhered to when considering what to set the full load current setting to. Should we adhere to the E3 manufactureres advice, or go higher as listed in sections 430.32 (A) and (C) of the NEC?

When ordering bi-metal relays I understand that they already account for the 1.25% as allowed for 1.15 S.F. motors in section 430.32A in the NEC, but what about when considering 140% bi-metal relays? If you decide to go with 140% as the protection value, then should an overload corrosponding to this current value be ordered, or is this value factored into aother range?
 

mayanees

Senior Member
Location
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Electrical Engineer and Master Electrician
cable sizing

cable sizing

philly,
As has been concluded, your motor is undersized for the application. And yes, per NEC 430.32 (C), you can take the overloads up to 140% of the motor nameplate rating provided the SF is 1.15 or higher.
... herein lies a rub I have with that NEC allowance, is that the cable was sized at 125% of the 430.250 nameplate listed amperage.
So now your subjecting the cable to a continuous overload and if you plot out the thermal damage curve with this new overload protection for a 125% sized cable, you're gonna damage the cable.
I ran into this problem with a submersible motor, such that whenever I do a design for a sumbersible pump now - I size the cable at 140% of the nameplate fla.
Certainly check the cable size, and any mitigating cable ampacity issues like ambient temperature derating, etc. before you subject it to a sustained 140%overload.

John M
 

Cold Fusion

Senior Member
Location
way north
CF thanks for sharing your info and experiences. ...
You're welcome Glad I can help.

... So I guess what you are saying is that hands down this is a poor design. ...
Well that got a chuckle out of me.:) Yeah - I might have possibly alluded to that.;)

... For the sake of discussion lets just say that it used 85% thermal capacity on a start. Obviously this would not allow a second consecutive start which most motors should per standards I believe. So seeing that this uses so much thermal on the start are we saying that it is a poor design? Would a better design have been a motor that only used somewhere around 50% thermal on starting? ...
There are several pieces tied up together here.

1. Using 85% of the thermal capacity to start is not necessarily bad. But if the motor is shut off (not tripped, just shut off), you will have to wait until the motor temperature drops to where there is only 15% TC used up, leaving 85% for a start. Maybe you only get one start per hour. If production can't stand for that you have a problem.

2. Let's say you can get it started, up to speed, running under normal load, then it trips on overload ocasionally - that's bad. There is only one way to fix this (Scotty ... I need more power)

Two separate issues:
High inertia loads take a long acceleration time and use up a lot of the thermal capacity and require a long time between starts. This is an application for a class 30 overload, or even jumping out the overload.

If the design is such that normal running conditions overload the motor - that is a different thing. The key here is ... the motor is overloaded. That means you need a... okay, you got it. This issue has little to do with overload class, or with high inertia load starting. Well, except for a couple of things. A bigger motor will accelerate faster, using less thermal capacity, will have more thermal capacity, and will be less susceptable to tripping on normal loading. And those are all good things.

Would a better design have been a motor that only used somewhere around 50% thermal on starting?
Yes. But better yet is a design that doesn't trip the motor on normal loading

... What about if the motor operates fine once it is up and running, but really only has problems with eating up thermal capacity during starting? Wouldn't a larger overload class help with this? ...
Only if it won't start. Say you put in a Class 20 overload, and the acceleration time is too long and the relay trips - but you haven't quite burned up the motor. So you put in a class30, and it does start. You are good to go.

But what if it tripped the c30 overloads starting, but still didn't quite burn up the motor? Then you shunt the overloads during starting. I've never had to do that. I'm thinking that when you hit the start button the first time, as jraef discussed, you are wondering, "Did I just let the smoke out".

I suspect that since the overloads are jumped, the operators have to be smarter than the overloads. There is nothing stopping them from stopping the motor and restarting immediately. I'd want a bunch of RTDs in the windings.

I'm not sure I understand this question. Other then setting the FLA, Overload class, and Overload reset value, what else goes into setting up the thermal model?
Okay, do you know you have those right?

...lets say the motor takes 85% to start and we set the overload reset to be when the motor reaches 70%. Even know the overload will clear the thermal overload and allow an attempted restart, we still will most likely be unsucessfull in the restart condisering we do not have enough thermal capacity avaliable. What are your experiences with setting this reset level or where should it be set?
None. That is so freakin tight on design it would worry the snot out of me. (and that is a disgusting sight:roll:) I mean what do you if somebody shuts a window and the ambient goes up 5 degrees. "Hey guys and girls, it's 81 degrees today, can't start the ID fan. Everybody can go home"

Your first post references the instruction manual which states to set the overload to 100% of FLA for 1.15 SF motors, and 90% for non S.F. Your last post then referenced you setting the overloads to 140% when you encountered a problem previously, and I also see that 430.32(C) of the NEC allows a setting of up to 140% for motors with a S.F. of 1.15. What guidelines should be adhered to when considering what to set the full load current setting to. Should we adhere to the E3 manufactureres advice, or go higher as listed in sections 430.32 (A) and (C) of the NEC?

Two different things:
AB E3+ account for the allowable setting above the FLA. The mfg charts on mechanical (bimetalic or alloy) also accounts for setting the relays above. The NEC 140% number does not. It is referenced to FLA.

.... What guidelines should be adhered to when considering what to set the full load current setting to. Should we adhere to the E3 manufactureres advice, or go higher as listed in sections 430.32 (A) and (C) of the NEC?
Sometimes the notes on the mfg charts allow you to jump to the next higher if you need. And if they do, I generally do. Never had a problem doing this.

And I have back calculated from the charts to what I figured was the actual long time overload trip current. Then forward calculated to the largest overload the NEC allowed. Is that reasonable? I don't know. Never asked an AHJ if it was okay. Never burned up a motor doing that. But I'm pretty certain I have shortened the life of few motors doing that.

If I were going to do some calculation and use that as a basis to push up an AB E3+, I certainly would not feel bad if I burned the motor up.

All the things you are discussing here are right on the edge of disaster. It is really good to know that if you go over the edge of reasonability and the equipment comes apart/burns up, you are absolutely positioned such that no one can get hurt.

Plenty here think I am a loose canon, but my basic premiss is, "Nobody gets hurt on my watch - no matter what." And I knew you are watching out for that as well.:)

I got to go to work - later

cf
 
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philly

Senior Member
There are several pieces tied up together here.

1. Using 85% of the thermal capacity to start is not necessarily bad. But if the motor is shut off (not tripped, just shut off), you will have to wait until the motor temperature drops to where there is only 15% TC used up, leaving 85% for a start. Maybe you only get one start per hour. If production can't stand for that you have a problem.

2. Let's say you can get it started, up to speed, running under normal load, then it trips on overload ocasionally - that's bad. There is only one way to fix this (Scotty ... I need more power)

Two separate issues:
High inertia loads take a long acceleration time and use up a lot of the thermal capacity and require a long time between starts. This is an application for a class 30 overload, or even jumping out the overload.

If the design is such that normal running conditions overload the motor - that is a different thing. The key here is ... the motor is overloaded. That means you need a... okay, you got it. This issue has little to do with overload class, or with high inertia load starting. Well, except for a couple of things. A bigger motor will accelerate faster, using less thermal capacity, will have more thermal capacity, and will be less susceptable to tripping on normal loading. And those are all good things.

O.K. so what I gather from all of this is if the overload is tripping during normal running conditions, then there is nothing that can be done, and simply changing the overload class will do nothing to help eliminate this problem. You simply need a bigger motor. In my case the motor runs fine under normal conditions, so most of my questions revolve around the starting aspect.

So if the overload is tripping when starting the motor for a high inertia load such as a fan with a long starting time, then this is a case where you can increase the overload class. It sounds like we are saying that by increasing the overload class we are not comprimising the normal running protection of the motor since the long time overload protection times for the different classes are similar? Are we comprising the motor by increasing the class and thus maybe allowing more starts, since the increased overload class may now allow more starting room?

What about a case where the motor runs fine under normal conditions, is able to start fine, but during starting uses a high amount of thermal capacity which may be a concern for a motor that needs to be restarted. Would this be an appropriate case for increasing the overload class, or only increase it if the motor will not start? Also my increasing the overload class this will have a second order effect of shortening the thermal decay which may also help as well.


None. That is so freakin tight on design it would worry the snot out of me. (and that is a disgusting sight:roll:) I mean what do you if somebody shuts a window and the ambient goes up 5 degrees. "Hey guys and girls, it's 81 degrees today, can't start the ID fan. Everybody can go home"

I'm not sure I follow what you are saying here regarding where to set the overload reset value at? Are you saying your not really sure? It sounds like to me that this value no matter what will be governed by what the motor needs to start?

Two different things:
AB E3+ account for the allowable setting above the FLA. The mfg charts on mechanical (bimetalic or alloy) also accounts for setting the relays above. The NEC 140% number does not. It is referenced to FLA.
cf

I'm a little confused as well on the overload ratings. So for the E3, if I set the value for the FLA of the motor, then will this take into consideration the 125% and 140% values that the NEC allows, or will it simply limit the overloads to the FLA value entered.

So lets say I have a case where a motor is sometimes running into the service factor of the motor, but the motor does not run continuously so it should be o.k. So we decide to let the motor run into the s.f. In this case would we set the E3 overload to a value corrosponding to 1.15% of the FLA representing the S.F. or set the value to 125% as referenced in the NEC?

I guess my confusion comes from when to select an overload value higher then the FLA such as the 125% or the 140%? Do we do this when the motor keeps tripping. If I understand everything you are explaining, then I gather that if the motor keeps tripping under normal operation then plain and simple, you need a bigger motor. However you can increase the overloads to the values shown in the NEC but this will most likely cause damage to your motor. These values in the NEC are maximum permissable values, but not advised values for running the motor at? Do I have this right?
 
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