2009GB/T 17215.421-2008 AC measurements - Tariff and load control - Part 21: Particular requirements for time switches
1998GB/T 9092-1998 Time switch for tariff and load control
GB/T 17215.421-2008 AC measurements - Tariff and load control - Part 21: Particular requirements for time switches has been changed from GB/T 9092-1998 Time switch for tariff and load control.