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Thread: Can you give me some input

  1. #1

    Default Can you give me some input

    Iím working on a refrigeration, and part of the system includes a heating system that draws a fair amount of power. The inlet could have as much as ~36A @220V, and we are planning on a 45A breaker. Do I need 10kAIC? What determines my AIC requirement?

    VRAJ TALATI

  2. #2
    Join Date
    Dec 2003
    Location
    Kent, WA
    Posts
    8,469

    Default

    Its a complicated question. First part is what is the minimum AIC required, and I think that is 5K in the US. So all breakers will be rated to withstand 10K AIC, and more if they are marked. Most I've seen are marked 10KAIC. So the question becomes: is that sufficient.

    The amount of fault current available depends on the system voltage, transformer size and impedance, and wire size and length. The highest fault current will be available from the transformer to the main disconnect. From there, the wires get smaller so less fault current is available. So to answer the question, you need to calculate what is available in your particular installation.

    I can tell you though that if you are using #8 copper wire and it is more than 25' long, I don't think it would be possible to draw more than 10K amps regardless of your service equipment.

    If the available fault current to that heating unit is more than 10K amps, then you need a branch breaker rated higher than 10KAIC or a rated series combination of breakers (main and branch) that allows you to use 10KAIC branch breakers because the main will protect it (e.g. 25KAIC main with 10KAIC branch can be used at 25KAIC in the branch if it is a listed series combination of breaker). Listed series combination breakers usually only come from the same manufacturer.
    Mark
    Kent, WA

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