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Thread: what is the SCCR of this circuit ??

  1. #11
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    Quote Originally Posted by xformer View Post
    After the Transformer a new SCCR is established.
    I believe you meant that a new SCCA is established. See my post #8 above.

    Charles E. Beck, P.E., Seattle
    Comments based on 2017 NEC unless otherwise noted.

  2. #12
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    Quote Originally Posted by charlie b View Post
    That is neither an SCCR nor an SCCA. That is an AIC - an acronym that has several possible meanings. I prefer "Amps Interrupting Capability," but other choices are available. It refers to the amount of current that can pass through the breaker's metal contacts without heating them up so severely that they melt together, forever thereafter preventing the breaker from opening.

    Forgot the fireball and mushroom cloud emoji.

  3. #13
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    Quote Originally Posted by charlie b View Post
    I believe you meant that a new SCCA is established. See my post #8 above.

    Yes.. That is correct. My apologies.

  4. #14
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    okay.

    i am confused all i know is, if i am building a panel who's name plate should read SCCR: 65kA.
    i need to have all my CB's (feeder circuit) rated at 65kA
    and all other component should also be rated at 65kA if they are part of the feeder circuit.
    some are excluded per S.B 4.2.1 (i.e filters reactors ..etc)
    Also, as i understand if i have transformer which doesn't have SCCR and is excluded per UL S.B 4.2.1
    anything after a transformer should not affect my the SCCR rating of the panel.

    do i make sense or do i have this completely wrong ??

  5. #15
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    Quote Originally Posted by samvivi7 View Post
    okay.

    i am confused all i know is, if i am building a panel who's name plate should read SCCR: 65kA.
    i need to have all my CB's (feeder circuit) rated at 65kA
    and all other component should also be rated at 65kA if they are part of the feeder circuit.
    some are excluded per S.B 4.2.1 (i.e filters reactors ..etc)
    Also, as i understand if i have transformer which doesn't have SCCR and is excluded per UL S.B 4.2.1
    anything after a transformer should not affect my the SCCR rating of the panel.

    do i make sense or do i have this completely wrong ??
    If you are building a panel whose name plate should read SCCR: 65kA,
    then all the breakers in the panel should have a 65kA rating or greater.

  6. #16
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    Quote Originally Posted by samvivi7 View Post
    i have two panels, my panel has a CB rated at 65kA with a transformer 15kVA which is feeding a second panel (third party vendor) rated at 5kA.
    So, do i have to have a 65kA CB with a 65kA transformer and the sub panel rated at 65kA ?
    You need to be very careful with your terminology. There are several things that need to be considered and they all sound similar, partly because they are all expressed in thousands of Amps, typically as kA.

    The Short Circuit Amps (SCA) or short circuit current available is the amount of current that can flow into a bolted fault condition. The starting SCA is often provided by the utility and then re-calculated at various points in the distribution system, such as after a length of conductor or a transformer. All equipment must be rated to handle the amount of SCA at its line side terminals. This value is may be calculated in the field. SCA is really what most people are asking for.

    Amps Interrupting Capacity (AIC) is a rating unique to protective devices that interrupt fault current, like breakers and fuses. This value is determined by the manufacturer based on testing. Devices should be selected so that their AIC exceeds the available SCA.

    Short Circuit Current Rating (SCCR) is the amount of fault current that a piece of equipment is rated to tolerate until a protective device operates clearing the fault. This value must be provided by the equipment manufacturer. There is no universal method for determining it in the field. Each type of equipment may get its SCCR value in a different manner. Panelboards, switchboards, disconnect switches, and motor control centers, may have a maximum tested/listed value with a label that limits its actual rating based on the field installed devices. An automatic transfer switch may have different tested SCCRs depending on the specific device protecting it. Control panels, like those built to UL508A, may have an SCCR calculated by the registered assembly shop, although many simply use the UL default value of 5kA.
    Last edited by jim dungar; 07-11-19 at 03:30 PM. Reason: typos
    Just because you can, doesn't mean you should.

  7. #17
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    I agree with Jim.

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