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3 pole contractor fed from 3 separate MCBs

vantech

Hi,

Any issue having 3x single pole (single phase) MCBs, switched by a 3 pole contactor, feeding 3 different runs of lights? The 3 circuits will be on different phases. There will be a separate neutral for each circuit. 

Each pole of the contactor is rated for the connected load and the number of lights it’s switching. 

Generally contactors are fed from an interlinked 3 pole MCB, however for this setup we need to use single pole MCBs to prevent 1 circuit tripping the other 2 runs of lights if there was a fault of the need to isolate one of the circuits. 

Don’t foresee it as an issue as long as the contactor is labelled as having multiple points of isolation. To me this is no different than a big grid switch, or a contactor fed from fuses. 

Anyone think otherwise?

Thanks. 

  • 0

    411.3.2.1 only applies to TN systems.

    Er, I read it as a general ADS requirement - the specific TN and TT bits don't start until 411.4 and 411.5.

    In TT systems, ...  for safe isolation (for safe working) all live conductors ought to be isolated.

    Agreed - but that can often be achieved by a different device from the one selected for ADS - e.g. a separate isolator or even a main switch.

       - Andy,

  • 0 in reply to AJJewsbury
    AJJewsbury said:
    Agreed - but that can often be achieved by a different device from the one selected for ADS - e.g. a separate isolator or even a main switch.

    I don't think we're at variance, Andy. If you read the other half the post of mine you replied to, I did say:

    Probably OK for most TN and TT systems, provided in TT at least there is a common means of isolation disconnecting all poles (including Neutral), but check special locations and other types of supply if applicable.

    Why did I pick out TT ... well requirements for isolation say that it's not always necessary to disconnect the Neutral for means of isolation in TN systems (Regulation 461.2).

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