Motor full load amps 3

[GJZ]

Is the full load amps rating on a motor's nameplate at the  rated horsepower on the nameplate or at the rated horsepower times the service factor, if any?

 

[azzmi]

Hi,<br>In general the current rating which is on the name plate is given for continuous operation. <br>Regards<br> <p>Azmi Demirel<br><a href=mailto:azzmi@elk.itu.edu.tr>azzmi@elk.itu.edu.tr</a><br><a href=

http://triton.elk.itu.edu.tr/~azzmi>Welcome</a><br>I

am handsome but married

 

[bufordwon]

On motor nameplates, the rated amps posted is the rated amps for the horsepower motor.&nbsp;&nbsp;On the service factor (sf) for example 1.15.&nbsp;&nbsp;sf x rated amps = full load in which the motor can handle.&nbsp;&nbsp;So in other words if a motor is pulling more amps then the nameplate says, check the service factor and times that to the rated amps and find out if that is exceeding the service factor amps.&nbsp;&nbsp;hope this helps

 

[jbartos]

Suggestion: Visit Reference
1. ANSI/NEMA Standards Publication/No. MG 1-1978 (or subsequent ones) &quot;Motors and Generators&quot;
a) Reference 1 Paragraph MG 1-1.43 &quot;Service
Factor-Alternating-Current Motors&quot; defines the Service Factor as follows
&quot;The service factor of an alternating-current motor is a multiplier which,
when applied to rated horsepower, indicates a permissible horsepower
loading which may be carried under the conditions specified for the
service factor (see MG 1-14.35). So, it is a good idea to look at it further.
b) Reference 1 Paragraph MG 1-14.35 &quot;Application of
Alternating-current Motors with Service Factors&quot; that states:
b.A) General. A general-purpose alternating current motor or any
alternating-current motor having a service factor in accordance with MG
1-12.47 is suitable for continuous operation at rated load under the
usual service conditions given in MG 1-14.02. When the voltage and
frequency are maintained at the values specified on the nameplate, the
motor may be overloaded up to the horsepower obtained by multiplying
the rated horsepower by the service factor shown on the nameplate.
When the motor is operated at any service factor greater than 1, it may
have efficiency, power factor and speed different from those at rated
load, but the locked-rotor torque and current and breakdown torque will
remain unchanged.
b.B) Temperature Rise - Integral Horsepower Alternating-Current
Motors. When operated at the service factor load, the motor will have a
temperature rise as specified in MG 1-12.42.1.b.
b.C) Temperature Rise - Fractional Horsepower Alternating-Current
Motors. When operated at the service factor load, the motor will have a
temperature rise as specified in MG 1-12.41, par. A.
That what the &quot;Bible&quot; says. Therefore, one must watch nameplate
motor rated voltage and motor rated frequency shown on the motor
nameplate when the service factor is used. This is a big risk since
everyone knows what those motors are getting at their terminals.
Therefore, simply, risks are fairly high, if the motor does not have a
rated frequency and rated voltage stabilizers (which can get expensive!)
while running within the service factor horsepower range.

 

[rhatcher]

jbartos is right that operating a motor at the service factor is a risky proposition.

To answer your question directly, the nameplate information on a motor is at 'full load'. Specifically, when operated at nameplate voltage and horsepower, the motor will draw nameplate amps and run at nameplate speed. If the voltage or load varies, the amps and speed will vary as well. Keep in mind though that the nameplate values for a 'production' (ie. mass produced) motor are based on a general standard for that motor and that individual motors may vary to a small degree.

 

[electricpete]

I agree with rhatcher and others on the direct response to the question: HP(&quot;nameplate&quot;=&quot;rated&quot = Sqrt(3)*FLA*Vnominal*eff*pf regardless of service factor. If we increase load by a 1.15 S.F. above rated, then both FLA and HP will be 1.15 times their nameplate value.

jbartos - Your response sounds like NEMA allows operation at S.F. load without any loss-of-life penalty as long as we maintain voltage and frequency. But don't forget the last paragraph of section 14.37.1 of MG1-1998 which reads:

&quot;A motor operating continuously at any service factor greater than 1 will have a reduced life expectancy compared to operating at its rated nameplate horsepower. Insulation life and bearing life are reduced by the service factor load.&quot;

In other words, you can expect reduced life if you operate continuously at S.F. load, even if you do maintain nominal voltage and frequency.

For more info on definition of service factor, I suggest you see responses to the thread &quot;service factor and safety factor of motor&quot; which was posted in this forum on 6/5/01 (sorry for quoting myself).

 

[electricpete]

I'd better correct myself before someone else does.

My equation:
'HP(&quot;nameplate&quot;=&quot;rated&quot = Sqrt(3)*FLA*Vnominal*eff*pf'
did not include proper unit conversion constant to make the left-hand side read in horsepower.

 

[jbartos]

Suggestion to the previous posting:
1. 1HP = 746Watts, therefore,
HPshaft = 3**0.5 x Vratedterminal x I x Pf x Eff / 746
2. &quot;A motor operating continuously at any service factor greater than 1 will
have a reduced life expectancy compared to operating at its rated
nameplate horsepower. Insulation life and bearing life are reduced by the service factor load.&quot;
///This statement may need some interpretations, namely, it is hard to maintain the exact rated frequency, ambient temperature, rated motor terminal voltage. Therefore, the motor reduced life expectancy is almost certain. However, one could possibly select material for the higher service factor motor that would even exceed the life expectancy of the regular motor at SF=1.\\

 

[rhatcher]

electricpete....you did point out that your equation was wrong before someone else did, but failed to correct it and therefore left it to jbartos to do so.

However, it is refreshing to see that you can not only recognize your mistakes but admit to them (definitely worth a star). I wish that all here were as forthright as I have seen some of our 'experts' go to great lengths to avoid being wrong. I won't mention any names but I think that you know who I mean.....;-)

 

[watter]

The full load amp rating on a motor's nameplate is at the rated horsepower of that motor's nameplate and should not be exceeded, at best you should size the motor for any application so that you are only using 80% of that motor's amp rating. The service factor (sf) should only be used as a multiplier to the full load amp rating to determine what size overload protection is required. This gives you a cushion in case the motor gets itself in a little bind of some sort.

 

[THooper]

As I have found from being a new member, rhatcher,electricpete,teco and jbartos, are always on TOP of the electrical issues and problems at hand, with respect of the points that have been given. One thing that hasn't been addressed is the factor of altitude. It is one thing that we have to take into consideration since we have customers that are mostly around 5600 feet and up to 8500 feet of altitude.

Motors having a service factor of 1.15 or higher will operate satisfactorily at unity service factor at an ambient temperature of 40 C at altitudes above 3300 feet up to 9000 feet.

Machines that are intended for use at altitudes above 3300 feet at an ambient temperature of 40 C should have temperature rises at sea level not exceeding values that would be calculated from the following formula:

Trsl=Tra[1-(alt-3300)/33000]

Where:

Trsl = test temperature rise in degrees C at sea level Tra = temperature rise in degrees C
Alt = altitude above sea level at which machine is to be operated.

For instance a 500 hp motor running at 8700 ft would need to be derated to approximately 420 hp.

In summary I feel that altitude should be considered for those of us in the high country. It shows that a motor rated for a certain horsepower must be derated to run at the proper rise.

Keep up the good work gentlemen,

Kind Regrds
motorhead1

 

[rhatcher]

Good point motorhead1. I would not have considered it seeing that the highest altitude motor at any of our customer locations is about 200 ft above sea level. This height is only by virtue of it being on a crane at the local port. The lowest motor(s) we have occasion to work on are about 160 ft below sea level, being high lift pump motors at a sewage treatment facility within sight of the ocean.

 

[jbartos]

Suggestion:
1. Reference
1. ANSI C50.41-1982 &quot;American National Standard for Polyphase Induction Motors for Power Generating Stations&quot;
Reference 1 indicates on page 7 in footnote 6 that &quot;For applications above 3300 Feet (1000 meters), the motor manufacturer should be consulted.
2. Would it be nice to have some References posted when it comes to equations, data, etc. to present the posting more traceable?

 

[THooper]

NEMA Offers the following information for motors operated at altitudes over 3300 ft. Reference 14.4.2, 14.4.3, 14.4, 14.4.1,

Also Reference 3.39 section three, AC Machines in EASA Technical Manual for temperature rise at high altitude operation.

The above Aug 2, post formula is from NEMA 14.4.3
Good point jbartos, I will keep that in mind when posting any information that can be reference.


Kind Regards,

motorhead1

 

[jbartos]

Thank you to Motorhead1. It is better to present something to the original posting rather than nothing, since the NEMA may or may not be followed.

 

[Wirenut]

I never liked running a motor over 80% of nameplate current. It make your motor last a long time. Spend the money on a properly rated motor and you will be able to sleep at night. Wirenut