Surely you mean Kva? How large is large. 6, 8, 18, 24, 60 bedrooms ??
100A 3 phase, as toasty says is 69kVA spread equally across the 3 phases.
If it's a 60amp supply then it's 230 x 60 / 1000 = 13.8KVA
If it's a 80amp supply then it's 230 x 60 / 1000 = 18.4KVA
If it's a 100amp supply then it's 230 x 60 / 1000 = 23KVA
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