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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. 

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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.

    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.

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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.

    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.

Children
  • 0 in reply to gkenyon

    Thanks 

  • 0 in reply to gkenyon

    I seem to be posting responses in the wrong area. Sorry. See below further question. 

    If for example the contactors coil is fed from a different circuit, perhaps a control circuit, and this trips or is switched off, this will obviously extinguish the lighting (assuming it’s a normally open contactor). 

    This will obviously not bring on the emergency lighting (as the supplies to the lights will still be on). I presume this is part and parcel of controlling lighting and something that would need to form part of a risk assessment. I have done DALI relays before, which operate the same way on power failure to the DALI circuit (if the control panel is switched off, lighting switches off).

    The emergency lighting will still always work on power failure or if the lighting circuit itself trips. 

    Thanks. 

  • 0 in reply to vantech

    Well that's always a risk, but if in a work environment, it should be under someones control, so the control circuit should not be turned off by  anyone but a person in control.

    To mitigate a tripping problem of the control circuit (though i think that is a very low risk), run the circuit from a CB. not a RCD, and keep the contactor close to the DB. It wouldnt trip through overload, and should not be tripped through a fault if the cable is protected properly, and CB sized correctly.

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