Índice
Quick Answer
An automatic transfer switch, or ATS, switches a load between two power sources.
When the main power fails, the ATS moves the load to backup power.
The backup source can be a generator, inverter, solar backup system, or another AC source.
When the main power comes back and becomes stable, the ATS switches the load back.
For LEEYEE ATS-63, the transfer switching time is less than 50 ms.
This is the ATS switching time only. A generator may still need extra time to start and stabilize.
Key Takeaways
- An ATS switches a load between normal power and backup power.
- A 2P ATS is commonly used for single-phase systems.
- A 4P ATS is commonly used for three-phase systems.
- Choose the ATS by current, voltage, pole number, and backup source.
- An ATS is not a UPS. It does not store energy.
- An ATS does not replace breakers, fuses, SPDs, or grounding.
- LEEYEE ATS-63 is available in 2P / 4P and 6A–63A options.
What Is an Automatic Transfer Switch?
An automatic transfer switch is a device for backup power systems.
It connects the load to one power source at a time. Usually, one source is normal power. The other source is backup power.
Normal power can be utility grid power. Backup power can be a generator, inverter, solar backup system, or another AC source.
The ATS watches the power sources. If normal power fails, the ATS switches the load to backup power when the backup source is ready.
The key idea is simple: an ATS is not just an on/off switch. It is a source transfer device.
What Does an ATS Do?
An ATS keeps the load connected to the available power source.
In a simple backup system, the ATS does this:
- It monitors normal power.
- It detects a power failure or unstable voltage.
- It checks the backup source.
- It transfers the load to backup power.
- It transfers the load back when normal power returns.
This reduces manual switching. It also helps keep important loads powered during an outage.
How Does an Automatic Transfer Switch Work?
An ATS monitors two power sources.
One source is the normal source. The other source is the backup source.
When normal power is available, the load stays on normal power.
When normal power fails, the ATS checks the backup source.
If the backup source is ready, the ATS transfers the load.
A typical ATS process looks like this:
- Utility power supplies the load.
- Utility power fails or becomes unstable.
- The ATS detects the problem.
- The backup source becomes available.
- The ATS transfers the load to backup power.
- Utility power returns.
- The ATS transfers the load back to utility power.
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LEEYEE ATS-63 has a transfer switching time of less than 50 ms.
This does not mean the whole backup system recovers in 50 ms.
If the backup source is a generator, the generator still needs time to start and stabilize.
If the load cannot accept even a short power break, use a UPS or another power design.
Automatic Transfer Switch Example
Think about a small building with utility power and a backup generator.
Under normal conditions, the building runs on utility power.
When utility power fails, the backup generator starts. When the backup source is ready, the ATS transfers the load.
When utility power returns and becomes stable, the ATS transfers the load back.
The same idea can also be used with solar inverter backup systems, distribution boards, pump panels, and small control cabinets.
Manual Transfer Switch vs Automatic Transfer Switch
A manual transfer switch needs a person to operate it.
An automatic transfer switch does the switching by itself.
| Tipo | How It Works | Typical Use |
|---|---|---|
| Manual transfer switch | Switched by hand | Simple systems where manual switching is acceptable |
| Non-automatic transfer switch | Electrically operated, but manually controlled | Systems that need powered operation but not full automation |
| Automatic transfer switch | Switches automatically based on source status | Backup systems that need automatic power transfer |
Main ATS Application Types
An ATS can be used in different source arrangements. The right choice depends on the power system.
Utility to Generator
This is one of the most common ATS uses.
Normal power is utility power. Backup power is a generator.
When utility power fails, the ATS transfers the load to generator power. When utility power returns, it transfers the load back.
Utility to Utility
In this setup, both sources are utility supplies.
If one source fails, the ATS transfers the load to the second source.
Utility to Inverter or Solar Backup
Some solar or battery backup systems use an ATS to switch between grid power and inverter output.
Check the inverter voltage, frequency, grounding method, neutral wiring, and local code before selection.
Open Transition vs Closed Transition ATS
Transfer switches are often described as open transition or closed transition.
Open Transition ATS
Open transition means break-before-make.
The ATS disconnects from one source before it connects to the other source.
This is common in general backup power systems. A short interruption may happen during transfer.
Closed Transition ATS
Closed transition means make-before-break.
It briefly connects two synchronized sources before disconnecting from the first source.
This is a more complex system. It is usually used in larger engineered power systems.
Important Note for Compact ATS Products
Do not assume every ATS supports closed transition.
Compact DIN-rail ATS products are mainly used for general backup source switching.
If your project needs zero interruption or source synchronization, use a different engineered power solution.
2P vs 4P Automatic Transfer Switch
Pole number is one of the most important ATS selection points.
Do not choose only by current rating. A 63A ATS may still be wrong if the pole number does not match the wiring.
What Is a 2P ATS?
A 2P ATS has two switching poles.
It is commonly used for single-phase systems where Line and Neutral need to be switched.
Typical 2P ATS applications include:
- Home backup systems
- Small shops
- Small offices
- Single-phase generator backup
- Single-phase inverter backup
- Cuadros de distribución residenciales
What Is a 4P ATS?
A 4P ATS has four switching poles.
It is commonly used for three-phase systems where L1, L2, L3, and Neutral need to be switched.
Typical 4P ATS applications include:
- Three-phase commercial systems
- Small factories
- Armarios de control
- Three-phase generator backup
- Pump control panels
- Distribution boards that require neutral switching
2P vs 4P ATS Selection Table
| Tipo de sistema | Common ATS Choice | Notes |
|---|---|---|
| Single-phase AC system | 2P ATS | Common for homes, shops, and small offices |
| Single-phase generator backup | 2P ATS | Used for L + N switching |
| Three-phase AC system | 4P ATS | Used for L1 + L2 + L3 + N switching |
| Three-phase generator backup | 4P ATS | Common in control cabinets and distribution systems |
| Inverter backup system | 2P or 4P | Depends on inverter output and wiring design |
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Simple rule: use 2P for many single-phase systems. Use 4P for many three-phase systems.
Final selection should always follow the actual wiring design.
How to Choose the Right Automatic Transfer Switch
Start with the power system. Then choose the ATS.
1. Confirm the Phase Type
Is the system single-phase or three-phase?
Many single-phase systems use 2P. Many three-phase systems use 4P.
2. Confirm the Load Current
The ATS current rating must match or exceed the load current.
LEEYEE ATS-63 is available in 6A, 10A, 16A, 20A, 25A, 32A, 40A, 50A, and 63A.
For motors, pumps, and compressors, also check starting current.
3. Confirm the System Voltage
The ATS voltage rating must match the system voltage.
LEEYEE ATS-63 supports AC110V, AC220V, AC400V, and 50/60Hz configurations.
4. Confirm the Backup Source
The backup source may be a generator, inverter, solar backup system, utility backup, or another AC source.
For inverter and solar systems, check neutral wiring, grounding, and local code.
5. Confirm the Transfer Switching Time
Transfer switching time tells you how fast the ATS changes from one source to another.
LEEYEE ATS-63 transfer switching time is less than 50 ms.
This is not the same as total backup recovery time. A generator may need extra time to start.
6. Confirm Manual and Automatic Operation
Compact ATS products often support both manual and automatic operation.
Manual operation is useful for testing and maintenance. Automatic operation is used for normal backup switching.
7. Confirm Installation Conditions
Check DIN-rail space, wiring space, terminal access, heat dissipation, cabinet layout, and installation environment.
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Key Specifications to Check Before Buying an ATS
| Especificación | What to Confirm |
|---|---|
| Tensión nominal | Must match the system voltage |
| Corriente nominal | Must match or exceed the load current |
| Pole configuration | Choose 2P or 4P by phase type and wiring method |
| Frequency | Check 50Hz or 60Hz |
| Transfer switching time | LEEYEE ATS-63 transfer switching time is <50 ms |
| Backup source | Generator, inverter, solar backup, utility backup, or other AC source |
| Protection design | Use proper breakers, fuses, SPDs, grounding, and cable sizing |
| Wiring diagram | Must match the actual system design |
A reliable supplier should provide technical data, dimensions, wiring diagrams, and selection support.
Standards and Compliance
Buyers often ask for CE and RoHS documentation for compact ATS products.
CE relates to applicable European conformity requirements for the declared product category.
RoHS relates to restricted hazardous substances in electrical and electronic equipment.
LEEYEE automatic transfer switches can be supplied with CE and RoHS documentation.
Project requirements can vary by country. For regulated installations, confirm local standards before ordering.
ATS vs MTS vs UPS
ATS, MTS, and UPS devices do different jobs.
| Device | Full Name | Main Function |
|---|---|---|
| ATS | Automatic Transfer Switch | Automatically switches the load between two power sources |
| MTS | Manual Transfer Switch | Switches the load by manual operation |
| UPS | Uninterruptible Power Supply | Provides temporary battery power during an interruption |
An ATS does not store energy. It only transfers the load.
A UPS stores energy in batteries. Some systems use an ATS and a UPS together.
Does an ATS Provide Overload or Short-Circuit Protection?
No.
An ATS transfers the load between power sources. It does not replace circuit protection devices.
A complete system should include the right breakers, fuses, surge protection, grounding, and cable sizing.
Common Automatic Transfer Switch Applications
Home Backup Power
An ATS can switch selected home circuits from utility power to generator or inverter backup.
Typical loads include lighting, refrigerators, routers, water pumps, and security systems.
Small Shops and Offices
Small commercial users may need backup power for lighting, cash registers, communication devices, refrigeration, or security systems.
Generator Backup Systems
The ATS transfers the load to generator power when utility power fails.
It transfers the load back when utility power returns.
Solar and Inverter Backup Systems
Some solar or battery backup systems use an ATS to switch between grid power and inverter output.
Always check inverter output, neutral wiring, grounding, load type, and local code.
Pump Control Systems
Pumps may need backup power in irrigation, drainage, and control cabinet systems.
For pump loads, check running current and starting current.
Telecom Cabinets
Compact ATS products can be used in telecom cabinets and remote equipment rooms.
Control Cabinets and Distribution Boards
An ATS can support auxiliary circuits, monitoring systems, fans, small motors, and backup circuits.
LEEYEE ATS-63 Automatic Transfer Switch
LEEYEE provides the ATS-63 series for compact backup power systems.
It is suitable for generator backup, solar inverter backup, small distribution systems, and control cabinets.
ATS-63 is a compact DIN-rail automatic transfer switch. It switches between power A and power B in AC systems.
It is available in 2P and 4P versions for single-phase and three-phase applications.
For full technical data, wiring details, and dimensions, view the ATS-63 product page or contact LEEYEE for selection support.
When ATS-63 Is a Good Fit
ATS-63 is a good fit for compact AC backup systems.
Typical uses include home backup, generator backup, and solar inverter backup.
It can also be used in small shops, light commercial distribution, control panels, and telecom cabinets.
Use it only when the current, voltage, pole number, wiring method, and transfer requirements match the system.
When ATS-63 May Not Be the Right Fit
ATS-63 is not a large power transfer system.
ATS-63 is not suitable for every system.
It is not intended for systems above 63A, data centers, hospitals, zero-interruption loads, or closed transition systems.
It also does not provide overload protection by itself.
For those projects, use a larger engineered transfer solution.
Common Mistakes When Choosing an ATS
Choosing Only by Current Rating
“I need a 63A ATS” is not enough.
You also need voltage, phase type, pole number, backup source, wiring method, and transfer time.
Using 2P ATS in a Three-Phase System
A 2P ATS is not suitable for a standard three-phase system that needs four-pole switching.
Ignoring Neutral Switching
Neutral switching depends on the grounding system, generator design, inverter wiring, and local code.
Undersizing the ATS
The ATS should not operate above its rated current.
For motors and pumps, also check starting current.
Treating ATS as a UPS
An ATS does not provide battery backup.
If the load cannot accept a short power break, use a UPS.
Forgetting Protection Devices
An ATS does not replace breakers, fuses, or surge protection.
When Should You Use an Automatic Transfer Switch?
Use an ATS when a load needs to switch automatically to backup power after the main supply fails.
An ATS is suitable when two AC power sources are available and manual switching is too slow or inconvenient.
It may not be enough for zero-interruption loads, unstable backup sources, unclear wiring systems, or oversized loads.
For sensitive electronics, use an ATS together with a UPS if needed.
Frequently Asked Questions About Automatic Transfer Switches
What is the purpose of an automatic transfer switch?
It transfers the load from normal power to backup power when normal power fails.
What is an automatic transfer switch used for?
It is used for backup power switching in homes, small buildings, generator systems, and solar inverter backup systems.
It can also be used in control panels, distribution boards, and telecom cabinets.
How does an automatic transfer switch work?
It monitors the normal source and backup source.
When normal power fails and backup power is ready, the ATS transfers the load.
What happens when utility power comes back?
The ATS transfers the load back to utility power after the source becomes stable.
Can an ATS work without a generator?
Yes. It can switch between grid power and inverter power, solar backup, two utility sources, or other AC sources.
Is an ATS required for a generator?
Not always.
But an ATS is useful when automatic generator backup transfer is needed.
Can an ATS switch between grid and solar inverter?
Yes, in some systems.
Check inverter output, voltage, frequency, neutral wiring, grounding, and local code first.
How fast does an ATS switch?
Switching time depends on the ATS design and source condition.
LEEYEE ATS-63 transfer switching time is less than 50 ms.
What is the transfer switching time of LEEYEE ATS-63?
It is less than 50 ms according to the product manual.
This is the ATS switching time only. Generator start-up time is separate.
What is the difference between ATS and UPS?
An ATS transfers the load between two power sources.
A UPS provides battery power during an interruption.
What is the difference between 2P and 4P ATS?
A 2P ATS is commonly used for single-phase systems.
A 4P ATS is commonly used for three-phase systems that switch L1, L2, L3, and Neutral.
Can a 2P ATS be used for a three-phase system?
No.
A standard three-phase system needs three-phase or four-pole switching.
What size automatic transfer switch do I need?
Choose by load current, voltage, pole number, source type, wiring method, and transfer requirement.
Can ATS-63 be used for home backup power?
Yes, when the voltage, current, pole number, and wiring method match the home backup system.
Can ATS-63 be used for generator backup?
Yes, if the system parameters and wiring design match the ATS rating.
Can ATS-63 be used for solar backup systems?
Yes, in some solar or inverter backup systems.
Check inverter output, voltage, frequency, neutral switching, and wiring method before selection.
What certifications are available for LEEYEE ATS?
LEEYEE automatic transfer switches can be supplied with CE and RoHS documentation.
Does an ATS provide surge protection?
No. Surge protection requires a separate surge protective device.
Does an ATS provide overload or short-circuit protection?
No. Use suitable circuit breakers, fuses, and other protection devices.
What should I confirm before buying an ATS?
Confirm voltage, current, pole number, and frequency.
Also check the source type, wiring method, transfer time, installation space, and certification needs.
Need Help Choosing an ATS?
Tell us your voltage, current, phase type, backup source, transfer requirement, and wiring details.
LEEYEE can help you select a suitable ATS-63 option.
Common uses include generator backup, solar inverter backup, distribution boards, and compact control cabinets.
Conclusión
An automatic transfer switch moves a load between normal power and backup power.
It is widely used in generator backup, solar inverter backup, and home backup.
It can also be used in small commercial systems, telecom cabinets, control panels, and distribution boards.
Before choosing an ATS, confirm the voltage, current, phase type, and pole number.
Then check the backup source, wiring method, transfer time, and installation conditions.
For compact backup systems, LEEYEE ATS-63 provides 2P and 4P DIN-rail options from 6A to 63A.
Its transfer switching time is less than 50 ms.
A well-selected ATS makes backup power switching easier, safer, and more reliable.
