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Thread: RLA verses FLA

  1. #1
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    RLA verses FLA

    Hey guys,

    I am once and for all looking for a straight forward answer...what is the REAL difference between Rated Load Amps (RLA) and Full Load Amps (FLA)? I read all of the popular trade magazines and have many books on refrigeration and electricity....but I cannot seem to get a REAL definitive answer to this question.

    Hope to hear from all of you!

  2. #2
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    Quote Originally Posted by singt View Post
    Hey guys,

    I am once and for all looking for a straight forward answer...what is the REAL difference between Rated Load Amps (RLA) and Full Load Amps (FLA)? I read all of the popular trade magazines and have many books on refrigeration and electricity....but I cannot seem to get a REAL definitive answer to this question.

    Hope to hear from all of you!
    singt,

    RLA: Acronym for "rated load amps". The maximum current a compressor should draw under any operating conditions. Often mistakenly called running load amps which leads people to believe, incorrectly, that the compressor should always pull these amps. You should never use the listed RLA to determine if the compressor is running properly or to condemn a compressor. The running amps of a compressor are determined by the evaporator temperature, condensing temperature and the line voltage.

    FLA - Full Load Amps: Changed in 1976 to "RLA - Rated Load Amps".

    Here's a link to more definitions.

    http://www.hvacrinfo.com/glossary.htm

  3. #3
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    then there is always confusion with term " run load amps" which means to me actuall running amps which should be within you FLA or RLA

    REGARDS STAN
    Keep it simple to keep it cool!

  4. #4
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    Rated load current [RLA or RLC] of a hermetic cooling compressor; is calculated by calculating the product of 64.1% of the maximum load current [MCC], and is set and marked on the name plate as [RLA], by the manufacturer.

    or

    "RLA est. a value for each compressor. This is 71% of the maximum continous current allowed by the motor protection system"
    Last edited by BigJon3475; 04-14-2008 at 07:03 PM.

  5. #5
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    Also, if you are dyslexic, don't confuse RLA with LRA which is:
    Locked Rotor Amps
    Also known as starting inrush, this is the amount of current the motor can be expected to draw under starting conditions when full voltage is applied.

  6. #6
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    "Running Amps" vary depending on conditons or load, never confuse with "RLA", for the various amp ratings view a compressor curve sheet"

    note on attached pdf curve sheet for a 4dl3A1500-TSK 480v, the amps range from 16.3 to 27.2 and RLA is 26.3

    if you are at -30/105 the amps should be 18.9
    if your amps are 26.0, you are over amping

    both Carrier and Copeland can supply you curve sheets
    Attached Images Attached Images

  7. #7
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    Quote Originally Posted by singt View Post
    Hey guys,

    I am once and for all looking for a straight forward answer...what is the REAL difference between Rated Load Amps (RLA) and Full Load Amps (FLA)? I read all of the popular trade magazines and have many books on refrigeration and electricity....but I cannot seem to get a REAL definitive answer to this question.
    Hope to hear from all of you!
    Here's my take on it. FLA is a rating for motors. RLA is a calculated rating for hermetic compressors and is only useful for sizing the circuit wiring, not for the technician to use for running characteristics. Here are is an excerpt from an article on RLA written by Joe Marchese of Coldtronics of Pittsburgh.

    "Why Not RLA?

    Most compressor manufacturers will stamp an amperage rating on their compressors. They will usually stamp the Rated Load Amp (RLA) of the compressor. However, the technician cannot use this value to determine the correct operating amperage.

    Also, trying to determine if a compressor is good or bad using RLA is not correct. It has nothing to do with what the correct amperage draw should be under its various load conditions.

    RLA is a mathematical calculation required to meet Underwriters Laboratories (UL) approval. The compressor manufacturer must run a series of tests to determine the Maximum Continuous Amps (MCA) before the overload trips. Once that has been determined, UL says to divide the MCA by 1.56 to determine the RLA. Some compressor manufacturers, such as Copeland and Carlyle, use a different factor. They divide the MCA by 1.44.

    If the RLA has any value, it is to determine at what amperage draw the compressor overload will trip, and to determine the fuse/circuit breaker size and the wire size."

  8. #8
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    ok so on a contactor when it says persay 50 res amps 40 fla amps .. what does the res mean ??

  9. #9
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    contactors in our industry are rated by fla
    contactors rated by res mean "resistive load", a steady load, as in strip heaters. The res rating is higher so be careful on your sizing!

  10. #10
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    Quote Originally Posted by hvac wiz 33 View Post
    ok so on a contactor when it says persay 50 res amps 40 fla amps .. what does the res mean ??
    We have three types of electrical "loads". Resistive, Inductive, Capacitive
    Only resistive and inductive are used to rate the ability of contact to handle the flow of current through an opening set of contacts. As mentioned resistive is pure resistance of usually heating elements. Inductive loads create a counter emf that is adding to the normal amps measured by a standard meter.
    keep your ice cold and flame hot

  11. #11
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    and then there is % RLA which is a good reference for the capabilities of your chiller. Its possible to use % RLA as a trigger for staging and unstaging an additional chiller.

  12. #12
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    Quote Originally Posted by dawgtchrr View Post
    We have three types of electrical "loads". Resistive, Inductive, Capacitive
    Only resistive and inductive are used to rate the ability of contact to handle the flow of current through an opening set of contacts. As mentioned resistive is pure resistance of usually heating elements. Inductive loads create a counter emf that is adding to the normal amps measured by a standard meter.
    I realize this is an old post however, counter or back emf actually reduces the amount of current drawn, not increasing it. The high initial draw of motors (compressors) is caused by the lack of back EMF until the compressor starts generating power (back EMF) then the current starts to be reduced - this the high LRA rating during start up and the the rated or running load amps after the compressor is running. Thanks!

  13. #13
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    Quote Originally Posted by snewman24 View Post
    Here's my take on it. FLA is a rating for motors. RLA is a calculated rating for hermetic compressors and is only useful for sizing the circuit wiring, not for the technician to use for running characteristics. Here are is an excerpt from an article on RLA written by Joe Marchese of Coldtronics of Pittsburgh.

    "Why Not RLA?

    Most compressor manufacturers will stamp an amperage rating on their compressors. They will usually stamp the Rated Load Amp (RLA) of the compressor. However, the technician cannot use this value to determine the correct operating amperage.

    Also, trying to determine if a compressor is good or bad using RLA is not correct. It has nothing to do with what the correct amperage draw should be under its various load conditions.

    RLA is a mathematical calculation required to meet Underwriters Laboratories (UL) approval. The compressor manufacturer must run a series of tests to determine the Maximum Continuous Amps (MCA) before the overload trips. Once that has been determined, UL says to divide the MCA by 1.56 to determine the RLA. Some compressor manufacturers, such as Copeland and Carlyle, use a different factor. They divide the MCA by 1.44.

    If the RLA has any value, it is to determine at what amperage draw the compressor overload will trip, and to determine the fuse/circuit breaker size and the wire size."
    you should always check the amps on the comp and keep in mind that the rla is figured when the room is the hottest.

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