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FLA Formal Definition
9

FLA Formal Definition

FLA Formal Definition

(OP)
I am stuck on FLA (Full Load Amps) for motors.
Where does the formal definition of FLA come from?
I suspect NEMA may provide that, but I cannot afford to purchase MG1 unless I know that contains the definition.

I find many code uses for FLA, but in NEC and in the Freeby Condensed MG1 I find no definition.

When I boldly try to define it myself, It gets sticky with Service Factors, Code Letters, etc.

How does a motor manufacturer determine FLA?

PUMPDESIGNER

RE: FLA Formal Definition

FLA is on the nameplate (I think you already knew that).

Roughly speaking it is the current the motor is expected to draw at rated voltage and rated load.

S.F. is a multiplier applied on top of FLA (ok, to be technical it is applied to horsepower.... I don't make a distinction but some in this forum will).

NEMA says FLA should be included in the nameplate. I don't think they come out and say it but I think my definition is good.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: FLA Formal Definition

(OP)
Thank you electricpete,
But how is FLA arrived at, how does the motor manufacturer determine an FLA?

I suppose what throws me is that FLA becomes mushy when you start to figure SF.  I have used FLA for years, I know what NEC says to do with FLA, but I really do not know what FLA is.  NEC does not define it, they just say what to do with it.

I try to define FLA as maximum rated current a motor can continuously draw without damage, but then service factor enters and now FLA does not really mean what I defined it as, because the SF means the motor can safely operate at higher current.

But then, NEMA MG1 9.15.1 states that the motor will have a shorter life if operated continuously in the SF.

So, my best guess now is this definition such as it is,
Ignoring all factors except winding insulation, FLA is the maximum rated current the motor can continuously draw to obtain “good” or “normal” life expectancy, but the motor can operate continuously in the Service Factor without short term failure, but life span will be reduced.

That seems like a mess to me, but that is how I see it at this moment.

PUMPDESIGNER

RE: FLA Formal Definition

Look again at what electricpete said:  "the current the motor is expected to draw at rated voltage and rated load."

This load is the rated horsepower on the nameplate.  

When operating in the service factor, the motor is producing more horsepower (above rated load) and will draw current above full load amps.  

RE: FLA Formal Definition

Full Load = Rated kW/((SQRT 3)*Rated kV*PF*efficiency).
This equals what electricpete said.
All design values are known to the mfr by design and tests.

1HP=0.746kW

RE: FLA Formal Definition

2
NEMA MG1 does not have a definition for Full Load Current.

However it has:

1.40 RATING OF A MACHINE.
“The rating of a machine shall consist of the output power together with any other characteristics, such as speed, voltage, and current, assigned to it by the manufacturer.”

1.47 FULL-LOAD TORQUE
The full-load torque of a motor is the torque necessary to produce its rated horsepower at full load speed. In pounds at a foot radius, it is equal to the horse power times 5252 divided by the full-load speed.

In my opinion, the full-load current has to be that defined with the machine rating.

All the rating parameters are defined by the manufacturer by calculation and prototype tests.

RE: FLA Formal Definition

I would agree with your summation Pumpdesigner, any operation of above FLA will reduce the life below that of normal expectancy.
Must remember NEC cares less about motor protection than it does about safety, hence the high overload settings according to NEC compared with NEMA.

RE: FLA Formal Definition

Comment: IEEE Std 100-2000 "Dictionary" does not define "Full Load Amperes (FLA)" or "Full Load Current"

RE: FLA Formal Definition

Suggestion: Visit
http://www.reliance.com/prodserv/motgen/b9652new/b9652.htm
for a definition of Full Load Current, which is often used instead of Full Load Amperes (FLA)
Namely:
FULL-LOAD CURRENT
The current flowing through the line when the motor is operating at full-load torque and full-load speed with rated frequency and voltage applied to the motor terminals.

RE: FLA Formal Definition

(OP)
I sorry for having to leave town, was anxious to read your posts.

OK, I have it now, just be nice to dense minds like mine and perhaps your patience will pay off.

FLA is the current drawn by the motor to produce the rated horsepower at specified conditions.

PUMPDESIGNER

RE: FLA Formal Definition

At what power factor would the manufacturer have determined the FLA?  Power factors in the real world vary all over the map, so to speak.

rmw

RE: FLA Formal Definition


Haven't earlier posts in this forum mentioned that the “bonus 15%" can be limited by variation from nameplate voltage/frequency, and particularly by voltage imbalance?
  

RE: FLA Formal Definition

PUMPDESIGNER,
I think you already have it, but this is how I teach it in training classes I put on and maybe this will help too.
It appears to me that you are looking at FLA as being a motor design criterium that has a definition. In actuallity, motor design criteria are speed, torque and to some extent efficiency and lifespan (lets leave out power fator for the moment, although rmw has a good point).

Once the motor has been designed and manufactured to perform to the first criteria, the FLA is simply a measurement made when they are met in the lab. So when you select a motor for your application, it is done by speed and torque. HP (or kW) is just the rating used by the manufacturer to describe these criteria in one term, and is the measurement unit the motor is sold by. FLA is the maximum that you can expect to see under those specific conditions, and is what your protction and control system must be designed around for safety and reliability.

Service factor is just a way for someone to stretch the limits of the criteria without running the risk of immediate catastrophy. You will however expect to sacrifice the  efficiency and/or expected lifespan criteria in the long run. Some OEMs routinely utilize the service factor rating of the motor as a continuous output, but they are usually only concerned with a lifespan long enough to satisfy a warranty. Other applications, as typified by valve operators for instance, are short duty cycles anyway so lifespan and efficiency become irrelevant. Demanding more torque, and therefore running into the SF amps, is a way of keeping the frame size down that will not sacrifice anything really significant. With cyclicle loads like compressors, SF is often used to allow for the increased loading during compression (loaded) cycles without sacrificing efficiency that would be lost by running a larger motor during unloaded cycles. The same would be true for pumps and fans where viscosity or density may be variable. SF leaves some headway for occasional increases in motor load.

"Venditori de oleum-vipera non vigere excordis populi"


RE: FLA Formal Definition

rmw:

A motor's power factor is fixed by design as stated on its name plate. What you are referring to is the system power factor. For example if you add PFC in parallel with the motor, the power factor upstream of the point of connection of the PFC only  improves, the pf between the point of PFC connection  to the motor remains unchanged.

RE: FLA Formal Definition

If you scroll down ten or fifteen threads you will find one named "Free corporate electrical courses". I urge you to take the one by Siemens. It only takes about 30 minutes or so. In the part about AC motors and drives it describes torque and FLA (with graphs) in very good layman's terms. It answered some questions I have had a long time as an electronic technician who bluffed his way in as an electrican so many years ago.

RE: FLA Formal Definition

(OP)
Thank you all for good comments.
I have never wanted to be an electrical guy, but am forced to face the issue at times, no one else around that knows anything on the job sites, so I end up having to watch out for myself to get my pumps taken care of.  You all have seen it out there, wire too small, circuit protectors too small, service too small, transformers too small, etc.

We established a company policy years ago that no pump would be used with an impeller than can load the pump into the service factor at every point on the pump curve.  This is a wonderful rule, we can take a lot of electrical abuse and still keep on tickin.  A whole lot of bad things are required to stop us.

Just for note, one of the largest pump manufacturers recently tried to sell us a pump that was listed in their books as requiring X horsepower, but when we tried to order it they wanted to provide it with 3/4 X horsepower, said that the motor manufacturer gave them permission to use that motor at the larger horsepower, even though they will not label the motor as such.

Another manufacturer caused us a problem, we had no accurate power data that we trusted on their pump, we were in a hurry so we just ordered the pump with the phrase, "Trim Impeller to Totally Non-Overloading".
In the field the pump was drawing exactly the entire service factor.  We called them, they claim that Non-Overloading" means not above the Service Factor.

OK, I learned one more thing I wish I never had to learn, you have to define non-overloading to these buggers.

PUMPDESIGNER

RE: FLA Formal Definition

Comment on the previous posting marked ///\\\
We called them, they claim that Non-Overloading" means not above the Service Factor.
///This is technically and theoretically correct. However, it is practically difficult to maintain the motor running at S.F.=1.15, for example, and simultaneously, keep motor rated frequency and voltage.\\\    

RE: FLA Formal Definition

(OP)
jbartos,
Thank you for your comment, I see it this way.
SERVICE FACTOR may have a technical agreed upon definition, which if you know of a source for that definition I would appreciate knowing it.

But SERVICE FACTOR generally means a fudge factor to account for field things that happen like voltage sag, a little unbalance, things like that which cannot be predicted.

For a pump manufacturer just to walk in and use that service factor without asking the customer means that there is no longer a service factor available.  Those suckers can't seem to resist the tempation to grab something that provides a little cushion and makes life a little easier, pushing us onto the edge, and shortening the life of the motor.

Which then leads to the question, why have a stinkin service factor?

PUMPDESIGNER

RE: FLA Formal Definition

Boy oh boy

what a lot of correspondence - i Think jbartos hit the nail on the head on his memo 26/3.

FLA = Mech kW/(Un x Sqrt3 x Cos Phi x Effy)

Of course, optimal PF & Eff'y are usually between 85%
& 95% of rated loads, thus it is actually possible to get a motor current higher than FLC when a lightly loaded machine is operating at a naff power factor and effeciency (ie an oversized pump motor running a long way down-curve).

_______________________________________
Colin J Flatters BSc(Hons) IEng MIEE MIIE
Electrical Engineer / Project Manager
Email - cflatters@colin7.demon.co.uk.

RE: FLA Formal Definition

Hi Colin,

I must disagree that an over-sized motor running open shaft or on a light load could draw a current greater than the motor's rated FLC. Granted, it will draw a fair magnetising current and the power factor will be poor, but the current will not approach FLC.

Are you perhaps looking at the motor's phasor diagram and meaning that the quadrature (reactive) component of current is greater than the in-phase component? This could well be true for the condition you describe.



-----------------------------------

Start each new day with a smile.

Get it over with.

RE: FLA Formal Definition

Comment on PUMPDESIGNER (Mechanical) Apr 2, 2004 marked ///\\\
jbartos,
Thank you for your comment, I see it this way.
SERVICE FACTOR may have a technical agreed upon definition, which if you know of a source for that definition I would appreciate knowing it.
///References:
1. NEMA MG-1
2. IEEE Std 100 "Dictionary"
Service Factor (general-purpose alternating-current motor) A multiplier that, when applied to the rated power, indicates a permissible power loading that may be carried under the conditions specified for the service factor.\\\
But SERVICE FACTOR generally means a fudge factor to account for field things that happen like voltage sag, a little unbalance, things like that which cannot be predicted.
///Yes and no. The service factor can be imagined as extra HPs built into the motor by the manufacturer, e.g. SF=1.15 would mean for the 500HP standard motor extra 75HPs. If the 575HP motor happened to be available, it would be equivalent to the 1.15 service factored motor. However, voltage sags more than 10%, voltage unbalance more than 2% or so are detrimental to standard motors as well as to service factored motors.\\\
For a pump manufacturer just to walk in and use that service factor without asking the customer means that there is no longer a service factor available.
///Absolutely correct. It is called fine tuning the motor-pump sets.\\\
  Those suckers can't seem to resist the tempation to grab something that provides a little cushion and makes life a little easier, pushing us onto the edge, and shortening the life of the motor.
///Absolutely correct. Money talks and keeps motor manufacturers in business.\\\

Which then leads to the question, why have a stinkin service factor?  
///Because not everyone is a sucker around. There are many many decent people around. For example, if there is a motor operated valve that has very hard unseating (a lot of sediment inside), a suitably rated motor with high SF helps.\\\

RE: FLA Formal Definition

Service factor is good for sizing your overloads. That's my take on it. I see the old 150HP pump motors running good looking clean. I see the new ones noisey and leaking brown substances. It is all about the money.

RE: FLA Formal Definition

(OP)
jbartos,
I respect your opinions and thank you for the answers.
I get into a foul mood now and then, after I read my post I was a little embarassed.
I would have written those things differently on a better day, and you are correct in all that you say.

I know I have a legitimate gripe which I think you agree with:
If the motor manufacturer provides a service factor,
Users have a choice to use it constantly,
Or leave that service factor for abnormal conditions.
All is fine if they act wisely.

But over the years I have found that the service factor means nothing to many pump manufacturers except one thing, When they buy a 100 hp motor with a 1.15 service factor, they consider that they bought a 115 hp motor and they use it that way if they can, and if you do not like that you must be on guard to stop them.  Drop your guard for even a moment, and you get the standard treatment, they take you right to the edge.

I suppose also that my viewpoint is that of a person not working in Alaska but in tropical climates, heat is our enemy and we get poor motor life if we are not careful.

PUMPDESIGNER

RE: FLA Formal Definition

Comment on the previous posting marked ///\\\
But over the years I have found that the service factor means nothing to many pump manufacturers except one thing, When they buy a 100 hp motor with a 1.15 service factor, they consider that they bought a 115 hp motor and they use it that way if they can, and if you do not like that you must be on guard to stop them.  Drop your guard for even a moment, and you get the standard treatment, they take you right to the edge.
///It is sufficient to turn off valve a little bit to have the motor delivering 100HP instead of 115HP. In time, there may be some sediment instead of slightly closed valve so that the motor will be delivering 100HP shaft anyhow instead of 115HP.\\\

RE: FLA Formal Definition

(OP)
jbartos,

Yup, some processes result in lower flow rates over time,

But other processes result in higher flow rates over time due to age and wear on the hydraulic components.  Irrigation systems are known for that behavior because each spray head has a nozzle, and each nozzle degrades over time becoming larger and larger, flow rates always increase on irrigation systems.

The second and ultimately the killer problem on irrigation is the fact that the pumps are often located in distant remote areas with lower voltage, smaller wire sizes, etc.  So, if the pump guys take every bit of slack out of motor performance then the motors begin running hotter.

PUMPDESIGNER

RE: FLA Formal Definition

But over the years I have found that the service factor means nothing to many pump manufacturers except one thing, When they buy a 100 hp motor with a 1.15 service factor, they consider that they bought a 115 hp motor and they use it that way if they can, and if you do not like that you must be on guard to stop them.  Drop your guard for even a moment, and you get the standard treatment, they take you right to the edge.

So very true! Especially in the fractional HP pumps!

Dont forget to add impeller wear, making the pump pump too much!

RE: FLA Formal Definition

My comment about Service Factor (SF) in electric motors is to agree with the simple statement posted by GOTWW.

It is the “Overload allowed” if all other parameters are per specifications (Voltage, Frequency, Ambient, etc)

Some of the differences between Rated HP and Overload HP are the “Torque-Speed curve”, including staring and breakdown, Inrush current, Temperature rise, Efficiency and Power Factor.

The Rated HP must comply with all the standard specified parameters.
The overload has only to be carried without motor damage.

And without doubt is all about the money.

RE: FLA Formal Definition

I think the key here is the motor will run at SF. The length of time it will run at this level may or may not be reduced depending on the ambient temperature. The OL results in an increase in operating temperature. Any increase above the temp rating of the motor then we start seeing the life reduced. This is what OL protection is for-to prevent an over temperature situation.
I would discourage operating a motor above FLA for any length of time. If it needs to be done, it may be done with a probability of reduced life. If the motor has embedded RTD's or thermocouples then this would be the best way to determine if operation at the higher current will indeed reduce the life. Granted, temperature will change slow compared to the current so it won't act as fast as an overload but the temp can certainly be checked and compared with running amps and ambient temp.   

RE: FLA Formal Definition

I am late into this discussion and a little suprised there is no mention of temperature until April 13th posts.  I think buzzp brings up a very important factor about motors and their ratings.

The definition of a motor is " an electro/mechanical device that is thermally rated".

RE: FLA Formal Definition

(OP)
oxilume, I liked that article and saved it.
buzzp does bring in the correct balance to things.
If I had a motor working in Alaska running at outdoor temperature, I would not worry about that SF at all, (Probably get concerned with the grease or oil on bearings though).

But, our stuff is mainly South Florida, Caribbean, South and Central America, hot, hot, hot.  We no likey to see SF used at all.

PUMPDESIGNER

RE: FLA Formal Definition

Comment on CB2 (Electrical) Apr 14, 2004 marked ///\\\
I am late into this discussion and a little suprised there is no mention of temperature until April 13th posts.
///Not quite. My previous posting point to the motor nameplate where the motor temperature parameters or limitations are addressed. Visit
http://www.ab.com/manuals/dr/Motors/Motors9_2.pdf
for: Figure 1 motor nameplate indicates the motor ambient temp 40C and "thermally protected"\\\
  I think buzzp brings up a very important factor about motors and their ratings.
The definition of a motor is " an electro/mechanical device that is thermally rated".

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