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Two three phase machines on one circuit

E95

Two isolators out of one MCB, each isolator feeding a three phase machine, with the feed to the second machine being taken from the incoming side of the first machine isolator, effectively a radial circuit without the sockets?

Is this an issue? I understand it's not common practice but I can't understand why it would be classed as unsafe provided the cabling was sized for the maximum load (Both machines on)?

Today a contractor implied this wasn't able to be done, however I can't really find anything in the regs to say so, does anyone have any ideas or is it nonsense?

Regards

Parents
  • 0

    I don't know of any current reg it's contravening either.

    A very long time ago regs did have stipulations along the lines that circuits rated 15A or higher could only serve a single "point" but while that's long since gone the collective memory and standard practices do sometimes seem to retain a shadow of such relics (rather like people being afraid of having single phase loads supplied from different phases in the same room).

    In terms of "how bad" such an arrangement is, that really depends on the circumstances. In general it's probably less than ideal - lack of discrimination, perhaps a need to oversize OPD & conductors etc. On the other hand if the two machines had a related function - e.g. one put things onto a conveyor and the other took them off - then having them both stop on a single fault might be seen as a definite positive.

    Most likely it's a bit of a botch when a new machine arrived and the existing DB was already full (or an extra correct sized MCB wasn't available).

    Worth checking the manufacturer's instructions w.r.t. maximum overcurrent protective devices too.

        - Andy.

Reply
  • 0

    I don't know of any current reg it's contravening either.

    A very long time ago regs did have stipulations along the lines that circuits rated 15A or higher could only serve a single "point" but while that's long since gone the collective memory and standard practices do sometimes seem to retain a shadow of such relics (rather like people being afraid of having single phase loads supplied from different phases in the same room).

    In terms of "how bad" such an arrangement is, that really depends on the circumstances. In general it's probably less than ideal - lack of discrimination, perhaps a need to oversize OPD & conductors etc. On the other hand if the two machines had a related function - e.g. one put things onto a conveyor and the other took them off - then having them both stop on a single fault might be seen as a definite positive.

    Most likely it's a bit of a botch when a new machine arrived and the existing DB was already full (or an extra correct sized MCB wasn't available).

    Worth checking the manufacturer's instructions w.r.t. maximum overcurrent protective devices too.

        - Andy.

Children
  • 0 in reply to AJJewsbury

    Thanks, yes it was effectively a botch, for some small workshop machines on a jig which didn't come with spare capacity in the distribution board

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