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Old incomer connected to four 3 phase cutouts help

Simon M
Hi all,


I have a very old incomer entering the building that then feeds to 4 x 3ph cutouts. You can see two of the 3ph cutouts in the pic.
9f8642aebed8db60e40f7a2578ffd3a3-original-02.jpg


The incomer says on it  - BI Callender's - 4E 150 x 3. I assume this means 3 x 150 Amps? Please do correct me if I am wrong.


1. What is the maximum power I can draw from this system?


2. If each of the 4 Three phase cutouts were loaded with 100 Amp fuses and I was to pull close to that from each fuse. what would happen to the incomer as this would equate to 1200 Amps!


3. Is connecting 4 3ph cutouts to this old beast a reasonable thing to do? Or is it ridiculous?


Many thanks

Simon
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  • 0
    AJJewsbury:
    But could the incomer in question be a fused neutral?

    I doubt they ever put a fused N on a 3-phase system - too much risk of frying loads with 415V L-N. AFAIK even in the old days N was only fused after the transition to '2-wire' circuits.


       - Andy.


    AFAIK, fused neutrals were primarily used on DC systems, and sometimes retained on AC systems that had formerly been supplied with DC.

    There are still existing fused neutrals on AC systems but I suspect that these were once DC.


    A far less common reason would be a system that whilst AC originaly, once had BOTH poles of the supply live. For example a 220 volt circuit derived from a 3 phase 4 wire system at 127/220 volts. That would REQUIRE a fuse in each pole of the supply, and this might have been retained when the installation was later connected between one phase and the neutral of a 3 phase 4wire system  at 240/415 volts.


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  • 0
    AJJewsbury:
    But could the incomer in question be a fused neutral?

    I doubt they ever put a fused N on a 3-phase system - too much risk of frying loads with 415V L-N. AFAIK even in the old days N was only fused after the transition to '2-wire' circuits.


       - Andy.


    AFAIK, fused neutrals were primarily used on DC systems, and sometimes retained on AC systems that had formerly been supplied with DC.

    There are still existing fused neutrals on AC systems but I suspect that these were once DC.


    A far less common reason would be a system that whilst AC originaly, once had BOTH poles of the supply live. For example a 220 volt circuit derived from a 3 phase 4 wire system at 127/220 volts. That would REQUIRE a fuse in each pole of the supply, and this might have been retained when the installation was later connected between one phase and the neutral of a 3 phase 4wire system  at 240/415 volts.


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