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150A Ring Final Circuit

Neil Annetts

I am after some help in calculating the curent carrying capacity of a ring final circuit wired in 16mm Tri rated singles!

From the book 16mm tri rated will take 100A. circuit no more than 10 meters long, all in steel trunking / DB enclosures etc.

Supplied from a Schnieder NSX160F with a 100 - 160A TMD unit.

I know there is a way of calculating this but for the life of me i cannot remember how to do it and no amount of Googling is being productive!

Some background on the reason - 8-row schneider Prisma panel with 6x 80A Multiclip bus bars. cannot wire each back seperatley without having 6 cables per phase at the MCCB so the thought was to wire a ring around the lot.

Any help would be greatly appreciated

 

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    Older versions of BS 7671 used to specify a general rule for ring circuits that the conductors had to have a current carrying capacity of at least 0.67x the circuit rating. (It was only later fudged to 20A for a 32A circuit to take account of 2.5mm2 T&E in thermally insulated walls and the move from 30A to 32A protective devices).

    But (as above) some consideration of your specific circumstances would be very sensible.

        - Andy.

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    Older versions of BS 7671 used to specify a general rule for ring circuits that the conductors had to have a current carrying capacity of at least 0.67x the circuit rating. (It was only later fudged to 20A for a 32A circuit to take account of 2.5mm2 T&E in thermally insulated walls and the move from 30A to 32A protective devices).

    But (as above) some consideration of your specific circumstances would be very sensible.

        - Andy.

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