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Single Pole vs Double Pole MCB/RCD

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  1. #1
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    Default Single Pole vs Double Pole MCB/RCD

    Can someone explain the difference uses and mechanics between a Single Pole and Double Pole MCB/RCD?

    Am I correct in assuming the single pole only switches the active and the double pole switches the neutral as well. If you have limited space in your switchboard is it ok for the electrician to install single pole rcd's or are they less safe?
    Regards
    el_caro


  2. #2
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    The diffrence is size only

  3. #3
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    So the pole actually only refers to the slot it occupy and not the internal switching?
    If they are the same electrically and approved why would anyone use a larger double pole mcb/rcd?
    Regards
    el_caro


  4. #4
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    Price and speed the double pole are easier to install and can be used with standard bus bars making them quicker and sometimes neater plus in a domestic house it usually makes no difference.

    Not all rcd's are made equal the single poles were cheaper but they are about equal to doubles when talking clipsal now at $35 but you can pick up cheap (made in china style) double poles for less than $15.

  5. #5
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    And space

  6. #6
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    if you had the space and were not overly concerned with price (want quality)would you recommend asking for double pole rather than single pole ?
    Regards
    el_caro


  7. #7
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    I would buy clipsal and wouldn't care if they were doubles or singles.
    i have all clipsal doubles in my house.

    It would only be of concern if you had limited space.

  8. #8
    2K Club Member chrisp's Avatar
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    Hmmm, are the terms 'single module' (width) and 'double module' (width) being confused with 'single pole' (one set of contacts) and 'double pole' (two sets of contacts) here?

    No laurels to rest on

  9. #9
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    Single and double pole is just the slang description of the products that we use to describe the width 18mm being one pole and 36mm wide being double pole it possibly stems from the fact there is no need to specify single phase for these units as a three phase rcd generally has four terminal connections and would be called a three phase rcd.
    Fundamentally they are both double pole (active +neutral), there are a few variants in design but from a basic description point of view they perform the same task and provide a minimum level of protection.
    To disconnect supply when current leakage occurs.

  10. #10
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    Quote Originally Posted by chrisp View Post
    Hmmm, are the terms 'single module' (width) and 'double module' (width) being confused with 'single pole' (one set of contacts) and 'double pole' (two sets of contacts) here?

    Yes that was what I was wondering also.

    Just found these as an example of the different types (poles) I was talking about. I too would prefer an electrician to install a recognized brand like Clipsal.

    2 POLE DIN RAIL MOUNT 20A RCD MCB RCBO SAFETY SWITCH SWITCHES WHOLESALE PRICE | eBay

    eBay Australia: Buy new & used fashion, electronics & home d
    Regards
    el_caro


  11. #11
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    You simply won't find an rcd that doesn't have both neutral and active contacts because it needs both to operate.

    For further information Residual-current device - Wikipedia, the free encyclopedia should cover it in detail.

  12. #12
    2K Club Member chrisp's Avatar
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    Quote Originally Posted by LinesElectrical View Post
    You simply won't find an rcd that doesn't have both neutral and active contacts because it needs both to operate.

    For further information Residual-current device - Wikipedia, the free encyclopedia should cover it in detail.
    The OP was referring to RCD/MCB combo units. The RCD indeed requires the active and neutral - however, the MCB part isn't necessarily double-pole switched. They mostly are, but there are exceptions. e.g. the Clipsal 4RCBE120/30 - the highlighted "1" indicates 1-pole.

    Question to the OP: Are you asking about (a) the pros and cons of 1-module RCD/MCBs vs 2-module RCD/MCBs, oe (b) the need for double-pole units?

    I suspect you are asking about 1-module vs 2-module. If so, and you have the room in your enclosure, use 2-module units (as per the elecos' responses above).
    No laurels to rest on

  13. #13
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    If you have the space I would go for the 2 pole RCD's. I have seen many single pole RCD's fail. I suggest this may be because of their limited ability to dissipate heat compared to the 2 pole variant. Also they have to be wired in a specific way which may be a problem

  14. #14
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    I have a bias towards two module if space allows because I have found that high current single module units can get a bit warm when all packed together (you just have to be a bit clever about how you arrange them, I think it is just a heat dissipation per surface area issue). Having said that I have only had a problem with "Brand X" units. Clipsal and Hager are my brands of choice and have been problem free. Two module units also make labeling easier!

  15. #15
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    Quote Originally Posted by chrisp View Post
    The OP was referring to RCD/MCB combo units. The RCD indeed requires the active and neutral - however, the MCB part isn't necessarily double-pole switched. They mostly are, but there are exceptions. e.g. the Clipsal 4RCBE120/30 - the highlighted "1" indicates 1-pole.

    Question to the OP: Are you asking about (a) the pros and cons of 1-module RCD/MCBs vs 2-module RCD/MCBs, oe (b) the need for double-pole units?

    I suspect you are asking about 1-module vs 2-module. If so, and you have the room in your enclosure, use 2-module units (as per the elecos' responses above).
    My understanding has increased and Yes I am in the end asking about asking about 1-module vs 2-module.

    Many thanks to everyone for your explanations and advice.

    I have reached the conclusion from the above discussion that I should be insisting on the electrician installing 2-module units of a better quality preferably Clipsal.
    Regards
    el_caro


  16. #16
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    Quote Originally Posted by el_caro View Post
    Am I correct in assuming the single pole only switches the active and the double pole switches the neutral as well.
    If you have limited space in your switchboard is it ok for the electrician to install single pole rcd's or are they less safe?
    Yes a single pole only switches the active and a double pole switches the active and neutral

    Quote Originally Posted by chrisp View Post
    Hmmm, are the terms 'single module' (width) and 'double module' (width) being confused with 'single pole' (one set of contacts) and 'double pole' (two sets of contacts) here?
    You are on the money here Chrisp (as usual). Two questions in one and the confusion between a double pole unit and a two module unit.

    A single module unit can come as either single pole (only switches active) or double pole (switches both active and neutral)

    Quote Originally Posted by chrisp View Post
    Question to the OP: Are you asking about (a) the pros and cons of 1-module RCD/MCBs vs 2-module RCD/MCBs, oe (b) the need for double-pole units?
    It looks like the consensus is that the two module unit is less likely to have thermal problems but is that just be because the single module units are being packed into small switchboards and the current density is too great. I would assume a well balanced (properly derated) and sized switchboard with single module units would be just as reliable as one with two module units.

    Can anyone come up with a scenario where a single pole RCBO would be less safe than a two pole one?

  17. #17
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    Quote Originally Posted by el_caro View Post
    if you had the space and were not overly concerned with price (want quality)would you recommend asking for double pole rather than single pole ?
    Double every time. But that is from an electricians point of view as the singles can be hard to terminate as the A and N are very close although offset but it is a squeeze to get cable in.

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