What Size Main Circuit Breaker For 10Mm Incoming Supply Cables?

[GavinK]

10mm cables supply the distribution board. The board has 8 circuits : 2x32A and 6x16A breakers which are sized correctly. Should the main incoming breaker on the board (and the RCD) be rated 63A or 45A ? Thanks for any help..

[electau]

For cables installed unenclosed in air 63A. for cables enclosed in air 50A.

[GavinK]

Thanks... the cable is in conduit, although 50% of the run is enclosed in a floor/wall and the other 50% surrounded by air.

[canopy]

How long is the run?

[Crossy]

Electau's ratings are at the conservative (safe) end, Bangkok Cables 10mm THW which is commonly used as the overhead feed from meter to house is rated at 70A in air although at an actual 70A it's getting pretty warm.

Things to consider are the actual rating of your meter (15/45?) and the length of the run, as over 50m or so volt drop becomes more important than the actual rating of your cable.

Most of the places I've looked at that have a 15/45 meter have 10mm THW and a 63A incomer.

[GavinK]

15/40 meter. The 10mm cables run from the first board to a second board. The run is c 20 metres. The 1st board is supplied from the meter on 16mm cable. The 10mm cables do not pass through the 1st board - they are spurred off the 16mm cables. Hope this is clear... Its the main breaker on the 2nd board I want to check the size of. Thanks.