Eurostar chief executive Richard Brown said the trains failed as they left the cold air in northern France and entered the warmer air inside the tunnel.

The Class 373 (UK designation)

When built, all train sets were tri-voltage being able to operate on 25 kV, 50 Hz AC (LGVs, Eurotunnel, High Speed 1, UK overhead electrified lines) and 3 kV DC (Belgian classic lines) using pantographs and 750 V DC (UK third rail network) using third-rail pickup shoes. The shoes were retracted when operating from overhead power, and prototypes were used for testing.[25] After the opening of High Speed 1, overhead electricity is available throughout the core network between London and Paris / Brussels and the third rail shoes became redundant and were removed. The railway links to the new London-based depot facilities at Temple Mills and to the East Coast Main Line and West-Coast Main Line are 25 kV overhead. Five of the SNCF-owned sets are quadri-voltage, being able to operate from 1500 V DC (French lignes classiques) in the south of France; these sets are used for London–Avignon and ski services.

British-designed asynchronous traction motors are used. There are four powered axles in each power car and one additional bogie in the adjacent passenger carriage. This layout was also used on the original SNCF TGV Sud-Est (PSE) sets. The six powered bogies therefore contain a total of twelve powered axles to haul the rake of eighteen carriages. Drawing up to 12 MW of power, the train has the lowest power-to-weight ratio of any train in the TGV family—a SNCF TGV Réseau set has eight powered axles, but is only required to haul eight passenger carriages.

The train design is able to cope with five different standards of overhead catenary: domestic catenary in each of Belgium, France and the United Kingdom; fixed-height catenary for the LGV lines and the taller catenary used within the Channel Tunnel. The Eurotunnel catenary is much higher as the tunnel is designed to accommodate the double-deck car-carrying trains and roll-on roll-off heavy goods vehicle trains. The train driver is required to lower and then raise the pantograph during the change from each catenary system.[...]