He was active in the social Protestant movement, believing that employers had responsibility for the welfare of workers, and should not just delegate this to the state.

[4] He was made a consulting engineer with De Dietrich, undertaking missions in Germany, Austrie, Russia, Spain and Algeria.

[5] In 1889 Gruner was named secretary general of the Comité central des houillères, a newly formed interest group of coal mining companies.

This group promoted regulation of accident insurance at an industry level and included Oscar Linder (1829–1917), Maurice Bellom (1865–1919), Léon Say (1826–96) and Jules Simon (1814–96).

[7] Gruner was active in the social Protestant movement, as were other Musée members such as Jules Siegfried (1837–1922), Charles Gide (1847–1932), Henri Monod (1843–1911) and Pierre-Paul Guieysse (1841–1914).

In Nïmes in 1891 he lectured on "The Responsibility for Accidents from a Christian Point of View", speaking as a president of the Fédération protestante and of the Société des missions évangéliques.

He argued that to letting the state organize accident insurance was to shirk a sacred social duty.

[6] In 1905 Gruner was appointed general administrator of the Kryvyi Rih iron ore company in Russia.

[4] At the start of World War I (1914–18) Gruner returned to the army and organized the batteries of Vincennes, directed an ammunition service then inspected in Russia (1914–16).