MI 79

The MI 79, also called the Class Z 8100, is a dual-voltage electric multiple unit built for line B of the Paris RER, which joins the RATP Ligne de Sceaux, electrified at 1.5 kilovolts direct current, to the SNCF northern lines at 25 kilovolts alternating current. A pneumatic exterior step lets one train serve both the high platforms of one side and the low platforms of the other. SNCF and RATP ordered it jointly, and the contract was awarded in 1979 to Alsthom and the Societe Franco-Belge, which Alsthom acquired in 1982 before the order was finished. The first sets reached testing in 1980 and all 110 units of the MI 79A and MI 79B orders were delivered by 1985, as four-car sets with aluminium bodies and a top speed of 140 kilometres per hour. Frost damage to insulation in 1985 and 1986 sidelined some sets, and a 2010 to 2015 refurbishment costing about 275 million euros renewed the interiors.