Apologies in advance for such a long write-up, but context is required for any replies to be worthwhile ... I have had a house in France for the last 30 years, which has been heated with the same oil boiler since I renovated the house 30 years ago. The boiler has finally packed up, and I can't get the spares needed to repair it. France will ban the installation of new oil boilers in 2021, so I'm looking into an air-to-water heat pump. The house is already heated with underfloor heating, which means that it should be a simple change of oil boiler to heat pump as the source of heat. Apparently the electricity supply in single phase is insufficient for the heat pump's requirements, so the heating engineer has suggested taking out a 3 phase contract. The electricity supplier will bring 3 phases to their meter box for me for free, and I am responsible for the rest on my side of their meter. The heating engineer got a quote for me for the conversion on my side of the meter and it comes to 2000 euros. I am shocked at the price, as I thought all that would be needed is to leave the house itself on it's current single phase and just have the motor of the heat pump on 3-phase. Am I wrong in thinking that I should need little more than a 3 phase RCD and a 3 phase MCB of the correct current ratings? MCBs in France switch both line and neutral so there should be no need for an additional 3 phase isolation switch between the 3 phase MCB and the 3 phase motor. I don't know if 3 phase RCBOs are that easy to come by nor whether they switch both line and neutral of each phase, so would appreciate any pointers if anyone is familiar with them. So... Breakers £100 for a 3 phase RCD + £100 for a 3 phase MCB OR £235 for a 3 phase RCBO (e.g. https://uk.rs-online.com/web/p/rcbo...V02DmCh0VBwk1EAQYAyABEgK5nPD_BwE&gclsrc=aw.ds) £100 for 10m of 3 phase cable £100 for an enclosure and a few accessories £250 for a day's work My rough calc shows roughly £650 to £700 for the job, but the price is 3 times that. Any clues why my calcs are so different from the quote?