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10kw 3 Phase A/C what type of protection is required?

Former Community Member
Former Community Member
Another query from a non-electrician, hoping to get some guidance from the experts on how to handle my air conditioner install.


So I am in a predicament where I have a 3 phase distribution box (PME, 100A, 400V phase to phase supply) that is fully populated by RCBO's and hence has no RCD of it's own so unsure of what protection to use at the main distribution box (DB).

Is it okay to use just a 3 pole MCB of the correct rating (20A) to protect the circuit supplying power till the isolator? Since there is no 4 pole RCBO from Hager unsure what I need to do for earth fault protection (if required).

Apparently 18th edition mandates RCD protection for all circuits? Appreciate your insights please.


Looking for options where I do not have to install a seperate consumer unit and all the protection can be done from the existing DB. Appreciate your help!


More details on the installation below,
  • DB - Hager Invicta 3 range

  • Mitsubishi Heavy Industries - 3 phase outdoor unit - 10kw (power supply from DB)

  • Mitsubishi Heavy Industries - Single phase indoor unit - (power supply from outdoor unit)

  • Power to outdoor unit: We have used 4mm 5 core SWA from the DB to a 4 pole IP65 isolator on the outside of the property (cable sheath is earthed using a earth cable crimped to the earth bar of the DB (same earth slot for the Aircon power supply).

  • Power to indoor unit: The compressor (outdoor unit) then uses SY cable to supply power and communicate with the indoor unit. I have used PVC table to protect the SY cable since it is not outdoor rated and put the cable inside plastic trunking so there is no exposed SY cable.

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  • Former Community Member
    0 Former Community Member
    mapj1:
    FaeLLe:
    mapj1:

    Presumably the RCBOs are all single phase with  neutral tail. If you need RCD protection for a load with a neutral connection, you will need a 4 pole sensing device and that will not fit a 1,2,3 bus bar.


    Not sure this is entirely correct, apologies if I have misunderstood your comment.

    As per my other comment post on this there seems to be devices out there that can take up an empty space and still work?




    I may have the wrong picture. you said the board is full of RCBOs - I was trying to ask how the neutral to them is organised.

    Also most 3 phase bus bar, and I am not familiar with this one, have tags that go L1 L2 L3 L1 L2 L3 , not

    L1 L2 L3  N L1 L2 L3  N. A repeat pattern of 4, rather than 3.

    An RCD or RCBO for a load with a neutral connetion, err, needs a neutral connection. 4 pole bus bar does exist but is not common.

    The bus bar line up  is all I was asking about. It is sometimes seen that the end tag of the bus bar is removed to allow a flying N tail, but it is not really a nice fix and needs to be done carefully and well insulated, or ideally avoided.




    The Hager Invicta 3 has a seperate neutral and earth bar that lets you have a Neutral for each circuit (including a single phase circuit); so you can have a seperate N from the Neutral bar for each L1, L2, L3.

    Plus Hager is all Made in France including the RCBO's, big fan of them !


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  • Former Community Member
    0 Former Community Member
    mapj1:
    FaeLLe:
    mapj1:

    Presumably the RCBOs are all single phase with  neutral tail. If you need RCD protection for a load with a neutral connection, you will need a 4 pole sensing device and that will not fit a 1,2,3 bus bar.


    Not sure this is entirely correct, apologies if I have misunderstood your comment.

    As per my other comment post on this there seems to be devices out there that can take up an empty space and still work?




    I may have the wrong picture. you said the board is full of RCBOs - I was trying to ask how the neutral to them is organised.

    Also most 3 phase bus bar, and I am not familiar with this one, have tags that go L1 L2 L3 L1 L2 L3 , not

    L1 L2 L3  N L1 L2 L3  N. A repeat pattern of 4, rather than 3.

    An RCD or RCBO for a load with a neutral connetion, err, needs a neutral connection. 4 pole bus bar does exist but is not common.

    The bus bar line up  is all I was asking about. It is sometimes seen that the end tag of the bus bar is removed to allow a flying N tail, but it is not really a nice fix and needs to be done carefully and well insulated, or ideally avoided.




    The Hager Invicta 3 has a seperate neutral and earth bar that lets you have a Neutral for each circuit (including a single phase circuit); so you can have a seperate N from the Neutral bar for each L1, L2, L3.

    Plus Hager is all Made in France including the RCBO's, big fan of them !


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