1. What Is an ATS? (Automatic Transfer Switch)
ATS = Automatic Transfer Switch,switches automatically to the backup source when the main source fails, and switches back automatically (or manually) once power is restored. Mandatory for Class 1 loads such as fire protection, hospitals and data centers.
2. Transfer Methods (3 Types)
| Method | Transfer Time | Application |
|---|---|---|
| Auto-Transfer, Auto-Return | 3–30s | Standard dual-source |
| Auto-Transfer, No Auto-Return | 3–30s | Requires manual confirmation |
| Fire Alarm Interlock | < 3s | Fire pumps and other emergency loads |
3. Time Delay Settings (Why It Can't Switch Instantly)
Transfer delay 3–30s, which prevents false transfers caused by momentary grid fluctuations. For emergency loads such as fire pumps, a fast transfer of 0–3s can be set.A time delay is mandatory, otherwise a momentary lightning-related outage would cause frequent transfers.
4. ATS Selection (by Current Rating + Number of Poles)
| Current | Switch Type | Number of poles |
|---|---|---|
| ≤ 100A | MCB contactor type | 3P/4P |
| 100–630A | MCCB + contactor | 4P |
| 630–2000A | PC-class integrated | 4P |
5. How to choose between 3P and 4P? (whether the N line is switched)
4P switches the N line(to avoid parallel N-line interference); 3P does not switch the N line. For TN-S systems such as fire protection and hospitals, 4P is recommended; for general industrial use, 3P is acceptable. Zhejiang Golden Unicorn builds to order.
FAQ FAQ
What is the ATS transfer time?
Typically 3–30s; under 3s for fire emergency.
What is the difference between ATS and STS?
ATS = mechanical transfer (seconds); STS = static transfer (milliseconds), more expensive and used in precision applications.
Does an ATS have to be 4P?
Not necessarily. In TN-S systems where the N line must be switched, use 4P; for general industrial use, 3P is acceptable.
How soon does the ATS transfer after a power outage?
A delay of 3–30s is set to prevent false transfers from momentary fluctuations.
Related pages:Technical notes · Products · Industries · Resource center · FAQ · Get a quote