Ring circuits - Are they a complaint method?

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JamieP
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Ring circuits - Are they a complaint method?

Post by JamieP »

I saw a question the other day that I didn't know the answer too and that was "are ring circuits legal in NZ"?

Now I don't know much about ring circuits, other than being big in UK and can have higher overcurrent protection levels and that also UK has fuses in there plug tops (feel like there was some relation between this).

I know in NZ we commonly use a radial system

Other than causing confusion to those not familiar with such circuits, can they be a complaint solution in NZ?
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gregmcc
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Re: Ring circuits - Are they a complaint method?

Post by gregmcc »

I'm not sure of the legality of ring circuits, but as they are generally not the way things are done in NZ and almost every electrician in NZ could easily be caught out if they came across one.

I came across one many years ago, a fellow employee done a sub board change in a commercial installation not realising that one of them was a ring circuit, the 2 wires in the fuse were split to 2 different new circuit breakers on different phases, could not figure out why one or both circuit breakers tripped when the other was turned on. Even if they were on the same phase there would have been 2 x 16 MCB's in parallel feeding a 2.5mm ring circuit, this would have made it non compliant.
Solution, re-instate the ring circuit on 1 MCB, label the tails in the board, label the outside of the board so the next electrician knew what to expect.
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Re: Ring circuits - Are they a complaint method?

Post by pluto »

They need the two final subcircuit tails at the switchboard position for active to be in the same MCB terminal and the same terminal on the neutral AND earth bus bars for the neutral and earth connections.

I would not recommend the provision inn the United Kingdom Wring Rules BS 7671 of using a higher protective MCB rating for use in NZ.

However the ring circuit will reduce voltdrop and reduce the EFLI of the final subcircuit.
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