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Comparison of Bolted to Arc energy question needs clarification

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  1. mcmahanrf is offline Junior Member Pro Subscriber
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    Comparison of Bolted to Arc energy question needs clarification

    Question reads:

    For a 480 V system, the arcing-fault magnitude relative to the available bolted- fault magnitude is approximately:
    a. 25%
    b. 50%
    c. 75%
    d. 90%

    I don't have the IEEE but this

    https://www.cedengineering.com/userf...%20Methods.pdf

    References the calculation, using that calculation gives values of around 70% tracking down to 50% as fault current goes up. There are several variables that are not addressed by the question but I thought 50% would be a safe bet, I was wrong. anybody have any incites?

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  3. bec51392 is online now NETA Level II Pro Subscriber
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    I looked through my IEEE 1584... not one mention of anything close to what you are looking at but I though all the arc fault calculations came straight out of the NFPA 70E. this is what I found...

    NFPA 70E INFORMATIVE ANNEX D.3 (PG60)

    D.3 Doughty Neal Paper.
    D.3.1 Calculation of Incident Energy Exposure. The following
    equations can be used to predict the incident energy produced
    by a three-phase arc on systems rated 600 V and below. The
    results of these equations might not represent the worst case in
    all situations. It is essential that the equations be used only
    within the limitations indicated in the deƒnitions of the varia‐
    bles shown under the equations. The equations must be used
    only under qualiƒed engineering supervision.
    Informational Note: Experimental testing continues to be
    performed to validate existing incident energy calculations and
    to determine new formulas.
    The parameters required to make the calculations follow.
    (1) The maximum bolted fault, three-phase short-circuit
    current available at the equipment and the minimum
    fault level at which the arc will self-sustain. (Calculations
    should be made using the maximum value, and then at
    lowest fault level at which the arc is self-sustaining. For
    480-volt systems, the industry accepted minimum level for
    a sustaining arcing fault is 38 percent of the available
    bolted fault, three-phase short-circuit current
    .
    The high‐
    est incident energy exposure could occur at these lower
    levels where the overcurrent device could take seconds or
    minutes to open.)

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  5. bec51392 is online now NETA Level II Pro Subscriber
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    Also found this? but all this data is extremely dated.


    NETA Handbook series II - Arc Flash vol. 2:
    Available bolted fault current The punch behind the arc fault
    magnitude. Recall that the magnitude of a low-voltage arcing
    fault is approximately 43-57% of the bolted fault value. This implies
    that systems with significant bolted fault currents will have
    elevated arcing current levels.

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