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Thread: Feeder Breaker settings based on 25' Tap Rule

  1. #1
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    Feeder Breaker settings based on 25' Tap Rule

    I am upgrading a small portion of a feeder system. I am using 25' tap rule for 3 Loads off of a 1600Amp Breaker. I sized parallel 350 to protect to one third of the 1600A.

    Tap one feeds a 400 Amp Disconnect to protect a previously installed 500 running to a distribution panel with a 600 Amp Main Breaker.
    Tap Two feeds an auxiliary switchgear with 2 loads 1. 350hp motor 2. 150hp motor. Both Motors are non-Continuous
    Tap Three feeds a distribution panel with a 600 Amp Main Breaker.


    Click image for larger version. 

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    For the Main Feeder breaker for this circuit 1600A Sensor:

    I am looking for help on why the LTPU cannot be set above 620 Amps?

    I want to ensure that there are no errand trips on the 1600 Amp Breaker.

    Thank you for your help!

    Brian

  2. #2
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    Quote Originally Posted by brian5 View Post

    For the Main Feeder breaker for this circuit 1600A Sensor:

    I am looking for help on why the LTPU cannot be set above 620 Amps?
    Where are you getting this information?
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  3. #3
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    Hard to see but looks like tap 2 is terminating in 800AT. No 'round up rule' allowed for taps. Would need to terminate tap 2 in 600AT maximum for starters.

    That will probably not be enough for your 500 HP of motor load. Sorry to say but the whole thing looks hooky to me.

  4. #4
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    Quote Originally Posted by smoothops10 View Post
    Hard to see but looks like tap 2 is terminating in 800AT. No 'round up rule' allowed for taps. Would need to terminate tap 2 in 600AT maximum for starters.
    Looks like 800 to me too. If he wanted to keep 2 sets he would need a minimum of 600 kcmil.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  5. #5
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    Answers

    Infinity, I am supplying the information to upgrade.

    Smoothops10, What is Hooky?

    How can I attach a better picture?

    I will try to explain better......

    Main Breaker (2B) is a 1600 Amp Breaker. I am looking for setting for this breaker based on the 25' Tap Rule.

    I based the 3 taps on parallel 350 to be greater than 1/3 of the 1600 Amp breaker. 350 Kcmil THHN I am using 350 amps per parallel feed. Giving me 700 Amps capacity per load.

    TAP 1 : I am installing a 400 Amp Fused Disconnect to supply the Control Room I- Line to Protect the 500 Kcmil THHN.

    TAP 2: Auxillary Switchgear 2B-1A feeds breakers 2B-1B, 2B-1C. 350HP & 150HP Non continuous Motors.

    TAP 3: SouthEast I-Line Panel has a 600 Amp Main Breaker


    I am looking for help in setting the main breaker. I feel the main breaker should be set at 1600 Amps. Based on the following

    Tap 1: 400 Amps
    Tap 2: 685 Amps
    Tap 3: 600 Amps

    Click image for larger version. 

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  6. #6
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    The 1600 amp 2B is fine if your load calculation says that 1600 amps is enough. The problem is the 800 amp OCPD at 2B-1A, it needs to be no more than 620 amps {310*2=620} to protect your parallel 350's or they need to be changed to 600 kcmil {420*2=840} to get you enough conductor for the 800 amp OCPD.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  7. #7
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    Quote Originally Posted by infinity View Post
    The 1600 amp 2B is fine if your load calculation says that 1600 amps is enough. The problem is the 800 amp OCPD at 2B-1A, it needs to be no more than 620 amps {310*2=620} to protect your parallel 350's or they need to be changed to 600 kcmil {420*2=840} to get you enough conductor for the 800 amp OCPD.
    Thank You

    Brian

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