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Thread: Calculating current based on start up or running?

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    Calculating current based on start up or running?

    Hi guys
    I've come across a tricky part in an installation involving compressors. According to the spec sheet I've been given they pull 105A on start up but only 44A running. So naturally I went to the SANS 1014-1 regs book to check sizing of the cable. The minimum size was 10mm (for clipped direct that is). The problem is the unit switches on and off quite often...would this affect my size of cable and if so what size would be recommended.
    Thanks

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    You would install cabling and mcb's according to the run current. The MCB's should tolerate the start current which is short in duration but still effectively protect the cabling. The volt-drop on starting would be a consideration, you don't want the voltage dropping below the operating range of the compressor even/especially on startup. The maximum cycling on/off per hour is normally specified by the compressor manufacturer, if it's cycling frequency is higher then I would suggest measures to reduce it but it wouldn't affect the cable sizing. You didn't state a cable length so I can't comment on whether 10mm is sufficient.
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    Thanks AndyD the cable distance is maximum 10M so it shouldn't have an affect. I do appreciate the help. I'd rather ask the question here than look like a tool ordering the wrong cable on site lol!
    What I have done though is ordered slow curve breakers to prevent start up tripping.

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