“Poly” simply means more than one “Polyphase” refers to two or more than two voltages (phase/s) having same magnitude and frequency but displaced from each other by an equal electrical angle. “Polygamy” more than one wife. Low voltage connctions available in the UK with more than one phase are Two phase 230V (phase to neutral) Split phase 230V (phase to neutral) Three phase 400V (phase to phase) Split phase 460V (phase to phase) Single phase 230V (phase to neutral) is different to two phase and split phase 230V (phase to neutral). Three phase supplies have their phases 120 degrees out of phase with each other (balanced) and are supplied with an optional neutral conductor, forming a Three Phase and Neutral (TPN) supply. TPN is common in low voltage supply’s, so each phase can be used for single phase circuits, that require a neutral. To hazard a guess, you were upgraded to a TPN supply to be more precise?
Yup, I called it 3-phase and you said it was polyphase, i had not heard it called by that name.
It kinda explains the different flavours of domestic supply.