Introduction to ATS

Automatic Transfer Switching Equipment (ATSE) is mainly used in emergency power supply systems with rated voltage not exceeding 1000V AC or 1500V DC, and interrupts power supply to loads during power supply conversion.


1.1 Transfer Switching Equipment

An appliance that converts one or several load circuits from one power source to another.

1.2 Automatic Transfer Switching Equipment

It consists of one (or several) transfer switch appliances and other necessary appliances, and is used to monitor the power circuit and automatically transfer one or several load circuits from one power source to another. In the electrical industry, it is referred to as ” dual power automatic transfer switch ” or ” dual power switch ” .


ATSE can be divided into two levels: PC level and CB level.

PC-level ATSE: It only completes the function of automatic dual power conversion and does not have the function of short-circuit current disconnection (it can only connect and carry);

CB-level ATSE: It not only completes the function of automatic dual power conversion, but also has the function of short-circuit current protection (can be connected and disconnected).

Use Category

3.1 Communication:

AC-31A/B resistive load;

AC-33A/B motor load or mixed load including motor, resistance load and 30% incandescent lamp load;

AC-35A/B discharge lamp load;

AC-36A/B Incandescent lamp load.

3.2 DC:

DC-31A/B resistive load;

DC-33A/B Motor load or mixed load containing motor;

DC-36A/B Incandescent lamp load.

Note: A represents frequent operation and B represents infrequent operation.

Environmental conditions

4.1 Ambient air temperature: +40℃ ~ -5℃ (UL has provisions in other standards).

4.2 Altitude not exceeding 2,000m.

4.3 Atmospheric conditions:

① Humidity. When the maximum temperature is +40℃, the relative humidity of the air shall not exceed 50%. At lower temperatures, higher relative humidity is allowed, for example, 90% at 20℃ (daily environment).

② Pollution level: Pollution level 2 (for household and similar use);

Pollution degree 3 (industrial level).

Industrial electrical appliances are generally suitable for pollution level 3 environments.

4.4 Overvoltage category (installation category): IV – power supply level (incoming line end), III – distribution level, II – load level (control electrical appliances).

4.5 Electromagnetic environment: Environment A (non-public power grid, with high interference sources), Environment B (public power grid, without high interference sources).

Basic principles of selection

5.1 The indicators that require special attention when selecting are: the rated short-circuit making and breaking capacity of CB-level ATSE.

5.2 In principle, ATS automatic transfer switch is not used as a short-circuit protection device, but only as a power automatic transfer switch.

5.3 The rated current of ATSE should be greater than or equal to the setting current of its upstream air circuit breaker.

5.4 Determine the switching mode according to the nature of each power supply and its different uses:automatic switching with automatic recovery , or automatic switching without automatic recovery.

5.5 According to the nature of each power supply, the priority power supply is designated or not designated; and related functions such us -voltage and under-voltage detection, frequency detection, phase loss detection, communication interface, electrical and mechanical interlocking, continuously adjustable delay conversion, etc. are determined to realize automatic, remote, emergency manual control, etc.