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Protection When Changing CSA

Les Spiteri
I have always went by the rule " when changing (lowering) csa of cable/wire then insert protection device", and further to that the second rule was "if its only a small run perhaps <2M then first rule need not apply". 


What is experience of everybody on this?


This particular application in design phase has an incoming 95mm cable in through a a switch disconnector which requires distribution to many smaller branch circuits. usually this application for me in control panels is simple as small currents (<30A) are in use but this larger requirement means the terminations get tricky having many different wire sizes.


Thanks Folks!33eaed845ccf5afaa1f80feb683c2254-huge-distribution.png
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  • 0
    Agree, the simple answer is a fuse board or MCB panel.  If the proposed switch disconnector is nearby then this need not incorporate a main switch.

    If the switch disconnector is remote then you will need a panel that has a main switch.


    Alternatively if this equipment is to be installed within a large control panel, then you probably dont need a dedicated enclosure as the control panel Is the enclosure. Connect the incoming cable to large DIN rail mounted terminal blocks. From these terminal blocks run suitable sized wire to each DIN rail mounted MCB or bank of fuses.

    The short conductors between the terminal blocks and the fuses or MCBs can be rated according to the load current.
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  • 0
    Agree, the simple answer is a fuse board or MCB panel.  If the proposed switch disconnector is nearby then this need not incorporate a main switch.

    If the switch disconnector is remote then you will need a panel that has a main switch.


    Alternatively if this equipment is to be installed within a large control panel, then you probably dont need a dedicated enclosure as the control panel Is the enclosure. Connect the incoming cable to large DIN rail mounted terminal blocks. From these terminal blocks run suitable sized wire to each DIN rail mounted MCB or bank of fuses.

    The short conductors between the terminal blocks and the fuses or MCBs can be rated according to the load current.
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