Motor FLA and PF amps on nameplate, sizing heaters?

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hockeyoligist2

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Something new to me, I have a new motor to install, 20 HP, 460 V. On the nameplate it has FLA 35 amps, next line down it has PF amps 40. Never saw this before. Do I size the heaters on FLA or PF amps? No paperwork with the new motor. The old motor I'm replacing has FLA of 35 and pulls 24 amps. We are replacing old motors with high efficiency motors to get a break from POCO.
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
20 HP, 460 V. On the nameplate it has FLA 35 amps, next line down it has PF amps 40.
What type of motor? T430.250 shows a FLC of 27A for this motor. (which in my experience is almost always higher than nameplate.

The old motor I'm replacing has FLA of 35 and pulls 24 amps. We are replacing old motors with high efficiency motors to get a break from POCO.
Again, something doesn't sound right here. High torque motor?
 

Jraef

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I think maybe you are mis-reading that nameplate. it probably says "SF Amps = 40". SF means Service Factor. Your motor probably has a 1.15SF, if you take 35 x 1.15 = 40A (and change). What they are saying is that if you choose to sacrifice the long term lifespan of the motor by running it into the Service Factor, it will draw 40A. Don't do it if you don't have to, it's a game played by OEMs who don't want to buy the next size up but don't care if the motor fries, as long as it does so after the warranty expires..

Example of Service factor Amps shown on a nameplate:
 
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dana1028

Senior Member
I think maybe you are mis-reading that nameplate. it probably says "SF Amps = 40". SF means Service Factor. Your motor probably has a 1.15SF, if you take 35 x 1.15 = 40A (and change). What they are saying is that if you choose to sacrifice the long term lifespan of the motor by running it into the Service Factor, it will draw 40A. Don't do it if you don't have to, it's a game played by OEMs who don't want to buy the next size up but don't care if the motor fries, as long as it does so after the warranty expires..

Example of Service factor Amps shown on a nameplate:
I have a question(s) with respect to applying 430.32(A)(1) - from OP

1. Because the nameplate shows a SF of 40A....do you consider this motor 'marked with a service factor'?

2. Do you consider this motor 'marked with a service factor' of 1.15? [the arithmetic => 40/35 = 1.143...which is less than 1.15]

When applying 430.32(A)(1) to size 'heaters' this 'marking' and the value of 1.15 matters.

Just wondering which way you would go when sizing the heaters.

I ask from an academic perspective.
 

Jraef

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I have a question(s) with respect to applying 430.32(A)(1) - from OP

1. Because the nameplate shows a SF of 40A....do you consider this motor 'marked with a service factor'?

2. Do you consider this motor 'marked with a service factor' of 1.15? [the arithmetic => 40/35 = 1.143...which is less than 1.15]

When applying 430.32(A)(1) to size 'heaters' this 'marking' and the value of 1.15 matters.

Just wondering which way you would go when sizing the heaters.

I ask from an academic perspective.
35 x 1.15 = 40.25A (that's why I said 40 and change), so if that motor says "SF Amps = 40" then yes, that means it is marked with a 1.15 Service Factor. But don't over interpret 430.32, which says overloads "shall be selected and rated no larger than the following minimum percentages
based upon the full load current rating, in amps, listed on the motor?s nameplate:" ... So you may size the overload protection for the Service Factor, but in my opinion you should not if you don't have to. Officially, NEMA MG-1 states that although a motor may be run into the SF when necessary, it also says something to the effect of "but you can expect that it will not perform to specification in other areas such as torque, efficiency and service life" (I don't have a copy of MG-1 on this PC therefore I'm going by memory here, so don't quote me exactly).

In addition, if you read the motor starter heater selection charts or dial adjustment procedures from most NEMA manufacturers, they usually tell you that the 125% for a 1.15SF motor is ALREADY factored into the selection chart, so don't make that common mistake of doing it AGAIN. You only alter it down if you have a 1.0SF (or unmarked) motor. With IEC overloads, they are all set for 115% for a 1.0SF, because IEC motors have no Service Factor (or 1.0 for all intents).
 

hockeyoligist2

Senior Member
Yes Jraef, I meant SF, I'm getting old and senile. I called the manufacturer and they said basically the same thing you posted. So I won't needing to change heaters on the starter. Also, it is a High torque motor for a gas compressor.
 
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