1, primary load. The load that will cause great political and economic losses or casualties due to power supply interruption is called Class I load. Such as important railway hubs, communication hubs, important international venues, important hotels, operating rooms in hospitals, and important biological laboratories. In addition to two independent grid power supplies, the power supply mode of primary load should also be equipped with standby power supply. The standby power supply is generally a diesel generator set or a DC battery set.

2. Secondary load. The load that power supply interruption will cause great political and economic losses or cause disorder in public places is called secondary load. For example, office buildings of local municipal governments, three-star hotels, first-class cinemas, libraries, museums, cultural relics and treasures at the prefecture level. Except for two independent lines, the secondary load should provide standby power supply according to the actual situation.

3. Except the primary load and the secondary load, all the others belong to the tertiary load. The third-class load has no special requirements for power supply mode, and generally adopts single-loop power supply.