DC systems (especially third-rail systems) are limited to relatively low voltages and this can limit the size and speed of trains and cannot use low-level platform and also limit the amount of air-conditioning that the trains can provide. This may be a factor favouring overhead wires and high-voltage AC, even for urban usage. In practice, the top speed of trains on third-rail systems is limited to 100 mph (160 km/h) because above that speed reliable contact between the shoe and the rail cannot be maintained. COUNT 5
QSN1 Why DC system can effect the speed of trains? ANS1 low voltages QSN2 Can DC systems use low-level platform? ANS2 cannot QSN3 Besides speed and size what else the low voltage of DC system can effect? ANS3 air-conditioning QSN4 What is the speed limit for third rail system trains? ANS4 160 km/h QSN5 What can become unreliable if the speed exceeds the limit of 100 mph for DC system trains? ANS5 contact between the shoe and the rail