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Using BS3871 MCB to protect ne submain

Alan B

Is it ok to connect a new submain to an existing spare 3 phase BS3871 MCB in a light industrial installation. The alternative is to change the entire main DB.

Submain will be clipped direct to wall and steel roof beam. It will feed a new 3 phase DB, probably equipped with two 3 phase 16A MCB's.

My understanding is that BS 60898 replaced BS3871 and the standards are similar, I am sure there are some differences, but do they make a significant impact on safety? In my mind providing they disconnect in the required time everything should be acceptable? Main risks will be after the sub board using modern devices.

Thanks

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  • 0

    The selection of the circuit-breaker to provide ADS for the addition to the circuit is included in the certificate, surely?

    Well, would you refuse to add an extra socket to an existing circuit, because it was protected by a BS 3871 MCB? I'd suggest that the requirement for existing kit is only that it is "adequate" to feed the alteration, rather than complying with every dot and comma of the current regulations. So far, I don't see the old devices undermining the safety of ADS itself - the blowing of a fuse isn't required to provide 3mm separation, so the isolation requirement is for maintenance rather than ADS per se, it would seem. If isolation may be provided by other means, it could be said that the existing is adequate, if not 100% to current standards.

       - Andy.

  • 0 in reply to AJJewsbury
    AJJewsbury said:
    If isolation may be provided by other means,

    It's making an assumption about the intent of 531.1.1, but I follow the logic.

    However, as discussed above, the older isolators likely to be present were made to very similar requirements, and tested to 2 kV only.

    From my perspective, given the industry guidance, and taking that at face value knowing what's in the older standards vs the current ones, I'm having to say "I don't know".

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  • 0 in reply to AJJewsbury
    AJJewsbury said:
    If isolation may be provided by other means,

    It's making an assumption about the intent of 531.1.1, but I follow the logic.

    However, as discussed above, the older isolators likely to be present were made to very similar requirements, and tested to 2 kV only.

    From my perspective, given the industry guidance, and taking that at face value knowing what's in the older standards vs the current ones, I'm having to say "I don't know".

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