Roof-line Earthing Switch in WAG9 Locomotive:Before undertaking any maintenance in the loco,the roof busbar must be earthed after lowering both the pantos.The two small yellow keys can only be released after the roof-line is properly earthed.These yellow keys in turn are used for unlocking a key multiplier in the machine room.The key multiplier has a series of keys to unlock various equipments in the machine room.