Sub Main

[ricicle]

If the 3 core SWA is being used for single phase then you use 2 core single phase rating as only 2 cores will be carrying current

 

[RobFurn]

Thanks ricicle. Shame no tables actually state that, they should seeing as though its very normal to use 3 core as 2 core and earth single phase. Even the draft 17th edition has no recomendation.

 

[Pensdown]

16.0mm² 3 core SWA will allow you a load of 68A (all your circuits at full load), over a distance of 50m.

I have not applied diversity.

16mm² is only suitable for 68amps if you ignore the volt drop in the rest of the system and allow the full 4% to be dropped in the new cable.

As this is a sub main I would normally only work on 2% (3% maximum) to allow for the VD in the mains supply cabling & final sub circuits.

For a design current of 63amps @ 3%VD a 25mm² just conforms but if the OP wants to use 16mm² cable the maximum design current would be 54amps max working on 3% VD in the sub main cable.

IMO before a 16mm² was selected to carry any more than 45amps a full end to end design would need to be done to ensure that it conforms.