I have just purchased a sunvic unishare 3 port heating control system to fit to my domestic hot water system. I was unaware however that it does not come with wiring. Whilst i feel confident in following the wiring diagram i was thrown slightly when i went to purchase the wiring as it appears to come in various amperage ratings. (The system currently has an old dial type timer fitted which switches both radiators and hot water on at same time so there is already a mains connection present.)How do i find out what wiring i should use?