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service factor of motor 2
- Thread starter sunloco
- Start date
Skogsgurra
Electrical
Yes, I would like to have a real good, in-depth explanation to that, too.
We don't use SF much in Europe and when we do, I have a feeling that we do not really know what we are talking about.
I know that a 1.15 SF motor can be overloaded a lot more - heard up to 80 percent for a limited time - than can a SF 1.0 motor. But there must be a lot more to it. Technical and historical reasons. Data, tables, nomograms. We want to hear it all!
Gunnar Englund
We don't use SF much in Europe and when we do, I have a feeling that we do not really know what we are talking about.
I know that a 1.15 SF motor can be overloaded a lot more - heard up to 80 percent for a limited time - than can a SF 1.0 motor. But there must be a lot more to it. Technical and historical reasons. Data, tables, nomograms. We want to hear it all!
Gunnar Englund
thewellguy
Electrical
The service factor refers to the amount of time that you can monentarily overload the motor. There is a time limit, I think it is 30 seconds but I can not remember.
The differ numbers refer to how much. For example a 10 hp motor with a 1.15 service facture means that it can be load to 11.50 hp or 10 hp x 1.15 sf =11.50 hp
The differ numbers refer to how much. For example a 10 hp motor with a 1.15 service facture means that it can be load to 11.50 hp or 10 hp x 1.15 sf =11.50 hp
Hello Sunloco,
The S.F is a factor by wich the motor can be overloaded beyond the full load, a 1.1 Services Factor means that the motor can operate at a 10% overload with out damaging, if a motor has a S.F of 1.0 then the motor has no overload capacity and probably will overheat if is overloaded for a period of time.For main breakers and Wire sizing You have to take acount the S.F Amperes, normally S.F * FL Amps.
Best Regards
Petronila
The S.F is a factor by wich the motor can be overloaded beyond the full load, a 1.1 Services Factor means that the motor can operate at a 10% overload with out damaging, if a motor has a S.F of 1.0 then the motor has no overload capacity and probably will overheat if is overloaded for a period of time.For main breakers and Wire sizing You have to take acount the S.F Amperes, normally S.F * FL Amps.
Best Regards
Petronila
- Thread starter
- #5
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1
- #7
A complete specification is in NEMA Specification MG-1 at
As I recall, the continuous HP rating for a motor is for an ambient temperature of up to 40 degrees C. The Service Factor rating is for operation at an ambient temperature of 20(?) degrees C.
As I recall, the continuous HP rating for a motor is for an ambient temperature of up to 40 degrees C. The Service Factor rating is for operation at an ambient temperature of 20(?) degrees C.
Hello Sunloco,
Lets asume you have 10 HP motor coupled to one Pump,for a S.F 1.0 motor the name plate motor´s amperage is 14 Amps.This motor is not designed to drawn more than 14 amps under normal conditions. But the pump sometimes requiere 15 amps, this is a 1 amp beyond the name plate, for it this s.f 1.0 motor will be overloaded.Yo will need a 10.7 HP motors but you don´t find this motor at trade, (The next hp is 15HP)so what to do??
You call to motor´s dealers and sayds I have this problem, then the recommend use a 10 HP S.F 1.1 Motor, so whats that?? this is a motor that could provide you 1.1*14 amps = 15.4 Amps. Now you can supply the overload to this pump
with out use of more spencive 15 HP motor (And maybe you need some arrangments to install because could be different FRAME).And with out risk to burn the motor.
Regards
Petronila
Lets asume you have 10 HP motor coupled to one Pump,for a S.F 1.0 motor the name plate motor´s amperage is 14 Amps.This motor is not designed to drawn more than 14 amps under normal conditions. But the pump sometimes requiere 15 amps, this is a 1 amp beyond the name plate, for it this s.f 1.0 motor will be overloaded.Yo will need a 10.7 HP motors but you don´t find this motor at trade, (The next hp is 15HP)so what to do??
You call to motor´s dealers and sayds I have this problem, then the recommend use a 10 HP S.F 1.1 Motor, so whats that?? this is a motor that could provide you 1.1*14 amps = 15.4 Amps. Now you can supply the overload to this pump
with out use of more spencive 15 HP motor (And maybe you need some arrangments to install because could be different FRAME).And with out risk to burn the motor.
Regards
Petronila
Skogsgurra
Electrical
I have bee in several spirited discussions on this issue, and one thng is for certain; there is no absolute agreement from anyone. NEMA clearly states that a motor can be run into the service factor percentage and makes NO distinction as to a time limit. Therefore, one can expect that a 10HP motor with a 1.15SF can be used on a load requiring 11.5HP. The concept of a "limited time" is purely a matter of prudence on the part of the user. NEMA does acknowledge however that when using the service factor one can expect a shortened motor life among other things. No values of how much or how long are stated, nor is there any mention of temperature rise derating. So what it means is that you can expect normal life and performance at the rated HP, but if you use it into the service factor, it will work but all bets are off on performance and life expectancy.
Because of this, many OEMs, especially pump and compressor OEMs, regularly utilize the service factor of motors in order to avoid going up one size in a given application. They only need it to last out the warranty period so the somewhat nebulous long term efects are not important to them (on the surface IMHO). On consumer goods and some industrial pre-packaged systems, this is often hidden by saying things like "developes XX HP" instead of actually stating a HP rating. People will argue all day as to whether that is a good idea or not, but I am just stating a defacto application.
Eng-Tips: Help for your job, not for your homework Read faq731-376![[pirate]](/data/assets/smilies/pirate.gif "[pirate] [pirate]")
Because of this, many OEMs, especially pump and compressor OEMs, regularly utilize the service factor of motors in order to avoid going up one size in a given application. They only need it to last out the warranty period so the somewhat nebulous long term efects are not important to them (on the surface IMHO). On consumer goods and some industrial pre-packaged systems, this is often hidden by saying things like "developes XX HP" instead of actually stating a HP rating. People will argue all day as to whether that is a good idea or not, but I am just stating a defacto application.
Eng-Tips: Help for your job, not for your homework Read faq731-376
jraef,
Yes, Try to be in acordance about this concept is very hard, I think the design manufacturers always are above the rated values because they want to keep your good names in Industrie, for it is possible some motors don´t fail quickly even overloaded, my point of view about the Services Factor is exposed in my last post, this is usefull when you have sligt or very short time overloads.
Thanks for your comments.
Regards
Petronila
Yes, Try to be in acordance about this concept is very hard, I think the design manufacturers always are above the rated values because they want to keep your good names in Industrie, for it is possible some motors don´t fail quickly even overloaded, my point of view about the Services Factor is exposed in my last post, this is usefull when you have sligt or very short time overloads.
Thanks for your comments.
Regards
Petronila
Skogsgurra
Electrical
Wise words from several keyboards there.
As I said, I have been unsure about service factor and how to use it. The NEMA paper pointed to by sreid probably says it all, but the practical interpretation varies a lot. The example with 80 percent "short term" overload with a 1.15 SF motor is what I have experienced in a machine specification. How many minutes "short term" actually is, is not specified.
I think that the less creative European way of doing it leaves less to be guessed. Rated power = Rated power - and that's it.
Gunnar Englund
As I said, I have been unsure about service factor and how to use it. The NEMA paper pointed to by sreid probably says it all, but the practical interpretation varies a lot. The example with 80 percent "short term" overload with a 1.15 SF motor is what I have experienced in a machine specification. How many minutes "short term" actually is, is not specified.
I think that the less creative European way of doing it leaves less to be guessed. Rated power = Rated power - and that's it.
Gunnar Englund
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1
- #14
A motor with a service factor of 1.0 reaches it thermal limit in a 40 degree C ambient right at nameplate load. This means that the motor's design life is acheivable at nameplate load and that its thermal limits occur at the same point.
A motor with a service factor of more than 1.0 does not reach its thermal limit at nameplate load but rather at some higher load. The motor's design life however, is only acheivable at nameplate load. Operation at levels above nameplate, ie, in the service factor range, will not result in overtemperature but will result in shortened motor life.
I guess the bottom line is that a motor with a service factor over 1.0 has extra thermal capacity built into it but not extra mechanical/electrical life.
Or, to look at it another way, you can get extra continuous output from a high service factor motor but it will cost you in motor service life.
A motor with a service factor of more than 1.0 does not reach its thermal limit at nameplate load but rather at some higher load. The motor's design life however, is only acheivable at nameplate load. Operation at levels above nameplate, ie, in the service factor range, will not result in overtemperature but will result in shortened motor life.
I guess the bottom line is that a motor with a service factor over 1.0 has extra thermal capacity built into it but not extra mechanical/electrical life.
Or, to look at it another way, you can get extra continuous output from a high service factor motor but it will cost you in motor service life.
An excellent little
you can learn a bit about S.F. there.
You should like this one Gunnar!
![[pipe]](/data/assets/smilies/pipe.gif "[pipe] [pipe]")
remember: An opinion is only as good as the one who gives it!
you can learn a bit about S.F. there.
You should like this one Gunnar!
remember: An opinion is only as good as the one who gives it!
NEMA MG-1 describes what an Open and TEFC motor Service factor by definition is, eg. ODP is 1.15S.F., and a TEFC is 1.0S.F.; however, many manufacturers make a 1.15S.F. TEFC motor. The motor can produce the 15% more horsepower using the service factor area of increased amperage, heat, and shortened life in continuous operation. The trade off is the life span of the motor.
Just remember - It is mostly about temperature. High temps hurt, whether by overcurrent (overload) or higher ambient.
A higher S.F. motor can be used to give you a little margin for either case.
In power plants, we typically specify motors to be 1.15 S.F., and that the motor must drive the load without going into the S.F. This provides some coverage for "unanticipated" load conditions, as well as some "extra life"!
A higher S.F. motor can be used to give you a little margin for either case.
In power plants, we typically specify motors to be 1.15 S.F., and that the motor must drive the load without going into the S.F. This provides some coverage for "unanticipated" load conditions, as well as some "extra life"!
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