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Circuit protection for distribution circuit

Can 3 individual mcbs(instead of a 3 or 4 pole mcb) be used for circuit protection of a 3 phase distribution circuit, where a 4 or 5 core swa is used? Is there a requirement that all phases must be disconnected in the event of a fault?

  • well if was 3 fuses they may not all go at once, and that is common arrangement. It rather depends on what is at the other end and if the load will care. Some types of rotating machinery do not appreciate 'single phasing' and need a dropout configured so that if one phase drops the thing is cut off, but that is normally in the control gear


  • There will be no 3 phase loads.

Reply Children
  • then you have no problems

  • That sounds like 3 SP circuits with a shared neutral even if they are all in the same cable. See the definition in Part 2 on page 31. The danger is that if one (or two) of the MCBs is opened, the neutral may still be carrying a current.