When we choose the dual-power automatic switch, we often encounter the "two-station" and "three-station" methods, and this method is wrong. According to the latest dual power national standard GB14048.11-2005, the dual power supply is divided into PC-level dual power supply and CB-class dual power supply according to the electrical level. Generally speaking, the two-station dual power supply means that the replacement contacts only contain common power contacts and backup power contacts. The three-station dual power supply, in addition to the position of the two office power contacts, contains a said "intermediate zero position". Many producers and distributors have exaggerated the utility of “intermediate zero position”, and whether the intermediate zero can be used safely for fire reset isolation inspection and repair lines.

The dual power automatic switch is different according to the application place, and is mainly divided into a normal dual power supply and a fire rescue dedicated dual power supply. The fire-fighting dual power supply is mostly used in fire-fighting pumps, emergency lighting, fire-fighting elevators, smoke-proof exhaust fans, etc. Once an electrical fire occurs, the dual power supply first needs to ensure the normal operation of the power-using facilities, if the fire-reset is started. It will have a major impact on the safe and continuous power supply of fire-fighting power sources in fire zones. For the normal type of dual power supply, the half-middle waist zero can break the non-fire-fighting power supply and play the role of fire safety. However, because the dual-power self-switching switch is usually used at the end of the circuit, once the fire breaks, the upper power supply is directly broken, and the fire-reset reset misses the actual meaning. The utility of the intermediate zero is not used to isolate the power supply during load inspection and repair. In order to ensure the safety of the person and facility that is responsible for the maintenance, the isolation switch must be used as the isolated power supply.

In addition, the dual-power automatic switch is provided to instantaneously change the backup power supply when the common power supply is abnormal, so that the line is continuously powered. Due to the relative complexity of the mechanism, the dual power supply with the intermediate zero is worse than the two stations in terms of changing the speed and the performance. In some industrialized countries, the dual-supply automatic switching switch without “intermediate zero position” is selected in the dual-supply tight power supply system to increase the reliability and stability of the power supply.