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Thread: Contactor ratings

  1. #1
    Gold Member Derlyn's Avatar
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    Contactor ratings

    Hi all

    Can anyone explain what the current ratings AC1 and AC3 actually mean in the attached brochure.

    Thanks in advance ... Derek

    https://www.l-osales.co.za/download-...ol-gear-s1.pdf


    Edit: Found the explanation.

    Next question. If one uses a 3 phase contactor to switch a single phase live connected in parallel through the 3 contacts, can it be assumed that the total load current will be shared equally through the 3 contacts ?
    Last edited by Derlyn; 23-Nov-21 at 09:24 AM.

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    Quote Originally Posted by Derlyn View Post

    Next question. If one uses a 3 phase contactor to switch a single phase live connected in parallel through the 3 contacts, can it be assumed that the total load current will be shared equally through the 3 contacts ?
    You can assume that it will be shared equally - Don't size to tight rather go one size up

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    Gold Member Derlyn's Avatar
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    Thanks GCE.
    Trying to use the smallest contactor possible for house supply. Big difference in price between a 65A and 35A contactor.

    I think I will go for about 30A. That should do it for a 63 Amp main breaker.

    Once again, thanks.
    Much appreciated.
    Derek.

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    Gold Member Derlyn's Avatar
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    This little project is not as simple as it seems. Trying it on my own house before offering it to any clients, of which there are many, waiting in anticcipation.

    The idea is to use a fridge safe and a contactor to delay the power resumption after loadshedding.

    Theoretically the supply will go through the main switch then through the contactor and supply the installation.

    Problem is that the fridge safe plugs into a plug. I will have to install a plug fed from above the contactor through a circuit breaker. Now, the problem is that this plug won't be on earth leakage so I have to install a seperate earth leakage just for this monitoring plug. Gets more complicated as one progresses.

    Derek

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    Diamond Member AndyD's Avatar
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    AC1 and AC3 refer to the type of load connected ie how capacitive or inductive is it. A normal heating element for example has a unity power factor (PF = 1) and would be classed as an AC1 load. A motor is an inductive load, it might have a power factor of 0.7 for example and it would be classed as an AC3 load.

    Because an inductive load causes a phase angle between the voltage and the current it causes more damage to switch contacts when it's turned on and off. In the old days we just used a derating figure of 50% if it was an inductive load but nowadays switches, relays and contactors often come with different current ratings specified for AC1, AC3 and even AC4 class loads. The AC3 current a contactor can handle will always be significantly less than the AC1 current. Sometimes the manufacture just derates the lifespan of the device ie it may be good for 60000 operations with an AC1 load or 10000 operations with an AC3 load.

    This is an old ducument but there's a full list of the load classifications on page 2.

    iec_contactors.pdf
    _______________________________________________

    _______________________________________________

  6. Thank given for this post:

    adrianh (24-Nov-21), Dave A (25-Nov-21), Derlyn (25-Nov-21)

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