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Thread: Indoor unit

  1. #1
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    Indoor unit

    I have gas furance indoor unit which uses 3/4 hp 120v fan for heating. No MOCP is provided. Is it because this is not hematric motor or compressor for heating? What would be properly size overcurrent protection be for that fan nec 2014?

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  2. #2
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    A disconnecting means would be required. It probably would not contain an OCPD, unless fuses are speced.

    The OCPD for short circuit and ground fault protection would prolly be the panel breaker.

    OCPD type and multiplier for start up current would be chosen per 430.52 , motor ampacity would be chosen from motor tables at end of 430, not the nameplate.

    overload protection is probably built into the motor given the size. nameplate should say or have “TP” as part of motor identification.
    "Electricity is really just organized lightning." George Carlin


    Derek

  3. #3
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    See T430.52. OL protection is a different story.

    Or what Derek said

  4. #4
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    Quote Originally Posted by jumper View Post
    A disconnecting means would be required. It probably would not contain an OCPD, unless fuses are speced.

    The OCPD for short circuit and ground fault protection would prolly be the panel breaker.

    OCPD type and multiplier for start up current would be chosen per 430.52 , motor ampacity would be chosen from motor tables at end of 430, not the nameplate.

    overload protection is probably built into the motor given the size. nameplate should say or have “TP” as part of motor identification.
    Does not tell me percent to us based on RLA or FLA. Also what about table 430.248 i cannot use that?

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    Quote Originally Posted by codequestion View Post
    Does not tell me percent to us based on RLA or FLA. Also what about table 430.248 i cannot use that?

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    Would 20 amp be ok?

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  6. #6
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    Quote Originally Posted by codequestion View Post
    Would 20 amp be ok?

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    Ok i got it nevwr mind percents are right there on table. So what about size of non fused disconnect itself for the fans. 20 amps non fused disconnect ok for the fans?

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  7. #7
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    Quote Originally Posted by codequestion View Post
    Does not tell me percent to us based on RLA or FLA. Also what about table 430.248 i cannot use that?

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    Why do you think you cannot use 250.248? You have a single phase AC motor.
    "Electricity is really just organized lightning." George Carlin


    Derek

  8. #8
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    Quote Originally Posted by codequestion View Post
    Ok i got it nevwr mind percents are right there on table. So what about size of non fused disconnect itself for the fans. 20 amps non fused disconnect ok for the fans?

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    What code section would or would not allow this? Look for motor disconnecting means in 430.

    What does it tell you?

    We can discuss your answer after you present one.
    "Electricity is really just organized lightning." George Carlin


    Derek

  9. #9
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    Quote Originally Posted by jumper View Post
    What code section would or would not allow this? Look for motor disconnecting means in 430.

    What does it tell you?

    We can discuss your answer after you present one.
    Would it be sized pwr nec 430.110 (C)(2)? 13.8x1.15 = 15.87 so 20 amps non fused disconnect?

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  10. #10
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    Quote Originally Posted by codequestion View Post
    Would it be sized pwr nec 430.110 (C)(2)? 13.8x1.15 = 15.87 so 20 amps non fused disconnect?

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    I would think 430.110(A) is more applicable. C is for combination loads.

    Same math though. HVAC loads are also usually considered continuous loads so I would multiply by 125% also, but a 20A disco still works.

    And you correctly used table amp value not nameplate.

    Nameplate value would have been used if one needed to size overloads/ heaters but small motors usually have internal thermal overload protection.
    "Electricity is really just organized lightning." George Carlin


    Derek

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