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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. 

Parents
  • 0

    Probably OK unless any part of it is in a situation or installation which requires all live conductors - line(s) and neutral - to be disconnected for isolation, because Reg 531.1 states (1st para) that devices for ADS shall be suitable for isolation.

    But only isolation of the line conductor is required - if the last line of 411.3.2.1 is to be believed...

      - Andy.

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  • 0

    Probably OK unless any part of it is in a situation or installation which requires all live conductors - line(s) and neutral - to be disconnected for isolation, because Reg 531.1 states (1st para) that devices for ADS shall be suitable for isolation.

    But only isolation of the line conductor is required - if the last line of 411.3.2.1 is to be believed...

      - Andy.

Children
  • 0 in reply to AJJewsbury

    411.3.2.1 only applies to TN systems. In TT systems, it is also permitted to disconnect only live conductors for the purposes of ADS, but for safe isolation (for safe working) all live conductors ought to be isolated.

    However, ADS is used in other circumstances which require all conductors to be disconnected, such as faults in IT systems, as there is no "earthed live conductor".

    Whilst I agree it's arguable there is no "Neutral" in IT systems (there could be a star-point conductor, but distribution of this is not recommended in IT systems - however, the OP does not describe whether the three single-phase circuits are connected to the same phase or different phases - we could have this situation in three circuits from an IT system or "floating generator" etc.

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