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

Former Community Member
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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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    mapj1:

    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.




    The Memshield arrangement is L1 L2 L3 N (covering L1) L2 L3 L1, etc. AFAIK, there is no reason why you should not put 3 of these RCBOs on each side of an 8 way board. Alternatively, you fill the gaps with SP devices or blanks.


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  • 0
    mapj1:

    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.




    The Memshield arrangement is L1 L2 L3 N (covering L1) L2 L3 L1, etc. AFAIK, there is no reason why you should not put 3 of these RCBOs on each side of an 8 way board. Alternatively, you fill the gaps with SP devices or blanks.


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