When we should use three phase supply to the house? All Questions › Category: Electrical Estimating And Costing › When we should use three phase supply to the house? 0 Vote Up Vote Down chetan shidling asked 5 years ago I need short information. 1 Answers 0 Vote Up Vote Down chetan shidling answered 5 years ago If your house load exceeds more than 8000 watts then you need to take three-phase supply. If your house load is less than 8000 watts then a single-phase supply is ok.