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Why is a switch fuse used?

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  • 16-03-2013 2:50pm
    #1
    darbar
    Registered Users Posts: 6 ✭


    Hi guys,

    This is probably a silly question :o,but I'm just wondering why a 63A switch fuse is used in a consumer board rather then an 63A MCB when the rest of the protection devices used are MCB's ,I'm puzzled due to the fact if there is a short circuit and the fuse trips it will need to be replaced.I tried Google for this and the results showed that MCB's have countless advantages over fuses and the only advantage the fuse has seems to be that it's cheaper.The ESB website state that switch fuses are used but no explanation as to why they are.So hoping someone could shed some light on this query for me.

    Thanks in advance
    -Darragh


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    #2
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,593 Mod ✭✭✭✭2011


    darbar wrote: »
    Hi guys,

    This is probably a silly question :o,but I'm just wondering why a 63A switch fuse is used in a consumer board rather then an 63A MCB when the rest of the protection devices used are MCB's ,I'm puzzled due to the fact if there is a short circuit and the fuse trips it will need to be replaced.I tried Google for this and the results showed that MCB's have countless advantages over fuses and the only advantage the fuse has seems to be that it's cheaper.The ESB website state that switch fuses are used but no explanation as to why they are.So hoping someone could shed some light on this query for me.

    Thanks in advance
    -Darragh
    As a general rule fuses operate quicker under short circuit conditions than an MCB.

    If an installation were to develop a short circuit it would be preferable to have the customers lower rated fuse operate than the fuse on the ESB's side (which is in a sealed unit and would require a call out).


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    #3
    darbar
    Registered Users Posts: 6 ✭darbar


    2011 wrote: »
    As a general rule fuses operate quicker under short circuit conditions than an MCB.

    If an installation were to develop a short circuit it would be preferable to have the customers lower rated fuse operate than the fuse on the ESB's side (which is in a sealed unit and would require a call out).

    Thanks for the quick reply so it's used as discrimination that the 63A will blow in the event of the short circuit rather then the 80A fuse on the ESB side.Is the fuse used then because if a short circuit occurs the element in the fuse will disintegrate instantaneously thus giving it quicker tripping times than the MCB that require contacts to open?


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    #4
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,593 Mod ✭✭✭✭2011


    darbar wrote: »
    Is the fuse used then because if a short circuit occurs the element in the fuse will disintegrate instantaneously thus giving it quicker tripping times than the MCB that require contacts to open?

    Yes.

    Fues are not only cheap, but they are very reliable under short circuit conditions. You will often see motors that have overloads for overload conditions backed up by fuses for short circuit protection.

    I saw this myself when a dead short developed across the busbars in a 3 phase sub distribution board. The board was protected by an MCCB set at 80A per phase, this did not operate.
    Instead the upstream 250A fuse blew taking out multiple distribution boards, the UPS and consequently the entire plant!


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    #5
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Fuses are more reliable under severe high current short circuits than MCBs


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