whats going to be connected to it? if you're putting 2 lighting circuits on it, i'd run a 1.5mm cable on a 16 amp breaker.
If you're putting a sauna, 5 ring mains, 2 ovens, an 8 burner lectric hob, 800 watts of halogen lights and 2000 watts of security lighting, then i'd run 25mm cable.
Please be clear about what you want on this new CU.
Are you notifying this to your lcoal countil's building control, as you legally have to?
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