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What is a contactor coil(K) with 3 contacts...

Discussion in 'Electronics & Electrics' started by Silhorn, Feb 14, 2010.

  1. Silhorn

    Silhorn Member

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    Hi,

    I have a question on something i am studying and it says to draw the symbol of a contactor coil (K) with 3 contacts.

    Is this referring to a relay with 3 contacts?

    If so, the only thing i can find is this:
    http://www.kpsec.freeuk.com/symbols/relay.gif

    Is this what the question is referring to?
     
  2. Sleepy Dude..

    Sleepy Dude.. Member

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    on/off/Signal?
     
  3. Code_Nerd

    Code_Nerd Member

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    The drawings I have seen and do use the symbol you have linked to for a contactor coil.
     
  4. Symon

    Symon Castigat ridendo mores

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    If you are using AS symbols what you linked to is a relay.

    The coils are drawn the same, but the actual contacts are drawn differently. Contactors have a semicircle on the contacts, instead of the triangle shape.
     
  5. OP
    OP
    Silhorn

    Silhorn Member

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    ok so this is the correct symbol except it has semicircular contacts than arrows.

    But, i think this only has 2 contacts doesn't it? What would a 3 contacts one look like?


    I just seen another question which says to just draw a "contactor contact". Ehh, i am confused.

    (Sorry, i am new to electronic diagrams, and only small part of my study covers this ATM)


    Also, does anyone know of a website where it has a list of australian electrical symbols?
     
  6. Odje

    Odje Member

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    And it has 3 poles or 3 separate sets of contacts.
     
  7. FireTech

    FireTech Member

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    The term 'contactor' is normally used for an AC device and 3 contacts would usually indicate it was for 3 phase use. Normally a 240v AC coil with 415v rated contacts.
    If they wanted a drawing of a 'relay' surely they'd use that term?

    Google revealed this but there may be more sources: http://www.ee.latrobe.edu.au/~gt/ele1edp/Lectures/Electronic-Wiring.pdf
     
  8. Code_Nerd

    Code_Nerd Member

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    What does the number of contacts have to do with phases?
     
  9. LostBenji

    LostBenji Member

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    Up a tower somewhere....
  10. Code_Nerd

    Code_Nerd Member

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    I think you are maybe thinking of terminals?

    The 'contacts' of a contactor are used by external devices to convey that the contactor has been pulled in e.g. PLC, Lights etc.

    See very quick example below of a contactor and 3 contacts being used in a motor starting circuit.

    [​IMG]
     
  11. FireTech

    FireTech Member

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    Terminals are the fixed connections on the contactor that the cables are fastened to using screws.
    Contacts are the fixed or moving pads (usually coated copper) within the contactor which physically connect or disconnect when the coil is energised or de-energised.
    The main ones are rated for the supply to the motor/lighting etc and auxiliary contact are used for signalling, hold on circuit etc. They're still contacts.

    The top three symbols adjacent the motor are the main contacts and others are just auxiliary contacts.
     
  12. Code_Nerd

    Code_Nerd Member

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    When referring to a contactor with 3 contacts, 99% of the time you are talking about the auxillaries and not the main supply contacts.
     
  13. Goth

    Goth Grumpy Member

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    This is a little off topic... but what exactly is a contactor?

    My understanding is that it's basically just a very large relay with a 240VAC low-current coil and very large, high current contacts that can switch large amounts of current at 240VAC (or higher voltages), right?
     
  14. FireTech

    FireTech Member

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    I tended to refer to them as 2 pole, 3 pole, 4 pole contactor without really referring to (auxiliary) contacts unless there was a specific requirement for an additional auxiliary module.

    Basically, yes. See Wiki below.

    http://en.wikipedia.org/wiki/Contactor

    They didn't have Wiki's when I was an apprentice. Come to think of it, we barely had personal computers back then either... :lol:

    Another difference is that contactors can be usually be maintained (replace coils, clean the contacts etc) whereas relays are usually disposable.
     
    Last edited: Feb 15, 2010
  15. Symon

    Symon Castigat ridendo mores

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    Correct. The contacts are silver plated copper pads that are brought together by the energisation of the coil. Notice on the drawing how the contacts have a little semicircle on the left hand line - the semicircle means it's a contactor (ie, high current), unlike the auxilaries which don't have it and thus are low current.

    Correct again, especially with the pole comment. With contactors the number of contact sets are called poles, so you have 2, 3 and 4 pole contactors. It's confusing if you specificy contactors by the number of contacts as you can have heaps of auxiliaries, so the way to do it is something like 3 pole + 2 NO, 4 NC for a 3 pole contactor with 2 normally open contacts, and 4 normally closed contacts.

    The way I explain it to apprentices is that relays go 'click click', but contactors go 'clunk clunk' :)

    Voltage doesn't really have anything to do with it, you can get contactors for 12V power systems. Basically relays operate in control circuits to switch small currents, contactors operate in power circuits to switch large currents.
     
  16. LethalCorpse

    LethalCorpse Member

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    This is all true, but still doesn't define the difference between them. I've also been a little hazy on the difference in terms of operation, though I could pick them out of a lineup without difficulty
     
  17. Pablo_H

    Pablo_H Member

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    maybe another difference is contactors are modular (can add auxillary contacts, can attach an overload). They are open (can change the relay coil for repair or to a different voltage) and other things can be repaired or replaced, ie easily field disassembled.
     
  18. 2xCPU

    2xCPU Member

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    No.
    There is no intrinsic difference between a contactor and a relay.
    It's exactly the same as the difference between a 'capacitor' and a 'condenser' or '1 Hz' and '1 CPS'. The names were simply adopted by different industries so long ago that the they have stuck.
    Symons 'click click' vs 'clunk clunk' differentiation is as good as any to tell them apart.
    It comes down to who uses them/where they are used rather than and physical or electrical difference.

    2.
     

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