Sebastian was born in Liverpool, England on 9 April 1864 . His birth was registered as Pietro Sebastiano Inocenzo Adhlmar Ferranti.
In 1871, the family were living in Liverpool, Lancashire, and showed:
Casar Farranti Head M 40 Paris, France
Julie Farranti Wife F 44 Leicester, Leicestershire
Vanda Szczepanowska Stepdaughter F 21 London, Middlesex
Ladislos Szczepanowska Stepson M 23 London, Middlesex
Sebastian Ferranti Son M 6 Liverpool, Lancashire 
Sebastian married Gertrude Ruth Ince on 24 April 1888, in St Pancras London. 
At the time of the 1901 England and Wales Census, Sebastian Z, Gertrude, Zoe Ziani, Basil, Vincent, and Vera De Ferranti were listed as living in Hampstead, London, along with Sebastian's mother Julianna De Ferranti, his cousin William H Donner, and five servants.
The 1911 census taken in Nether Padly, Grindleford, Derbyshire, England shows the family, which is comprised of Sebastian age 46, an electrical, civil and mechanical engineer, his wife Gertrude, age 41 and children Basil, Vera, Yolande and Denis 
↑ "England and Wales Census, 1901," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:X983-5NH : 29 August 2015), Vincent De Ferranti in household of Sebastian Z De Ferranti, Hampstead, London, Middlesex, England; from "1901 England, Scotland and Wales census," database and images, findmypast (http://www.findmypast.com : n.d.); citing Hampstead subdistrict, PRO RG 13, The National Archives, Kew, Surrey.