In modern facilities, outages can halt operations, damage sensitive equipment and put lives at risk. That’s why robust standby power systems are a must.

Two components often mentioned in the same breath are the automatic transfer switch (ATS) and switchgear. They work together to ensure power from the utility or a generator reaches your equipment safely and reliably. However, they serve very different functions.

This article explains what each device does, how they differ, the types of ATS available, and when you might need one or both.

What Is an Automatic Transfer Switch?

An automatic transfer switch (ATS) is a self‑acting, power‑switching device governed by microprocessor‑based control logic. Its job is to ensure continuous delivery of electricity from one of two sources to a connected load.

When the primary power source (usually a utility connection) fails or falls outside acceptable voltage and frequency limits, the ATS automatically commands a standby generator to start. Once the generator output is stable, the switch disconnects the load from the utility and connects it to the generator, providing power with minimal interruption. When utility power is restored, the ATS switches the load back and shuts down the generator.

ATS: Automatic Transfer Switches

Large industrial systems use separate ATS units rated for higher currents. Transfer switches also come in manual and non‑automatic versions; these require human intervention to initiate a transfer, whereas an automatic transfer switch senses the outage and acts on its own.

Why Automatic Switching Matters

Automatic operation eliminates the need for an operator to manually throw a breaker in the middle of a blackout. In hospitals, data centers and manufacturing plants, even a few seconds of power loss can damage equipment or compromise safety. An ATS keeps power flowing without delay, protecting sensitive loads and preventing downtime.

How an ATS Works: Step by Step

Monitoring: The ATS controller continuously monitors voltage and frequency on the utility and generator sources.
Detection & decision: If the utility supply drops below preset limits, the controller signals the generator to start.
Generator startup: The generator cranks and reaches operating speed and voltage. In the meantime, the ATS remains connected to the utility supply.
Transfer: When the generator output is within tolerance, the ATS disconnects the load from the utility and connects it to the generator, restoring power to the facility.
Retransfer: Once the utility supply returns to normal, the ATS switches the load back to the utility and shuts down the generator.

Many ATS controllers also include test modes that allow facilities staff to simulate an outage and verify that the transfer mechanism works correctly without disrupting power.

Types of Automatic Transfer Switches

Automatic transfer switches come in several types, each designed to meet specific needs and power priorities. Understanding these options helps you choose the best ATS for your facility. By comparing ATS types, you can focus on reliability, speed, and suitability, making sure your equipment and operations get the protection they need.

Table: Automatic Transfer Switch Types, How It Works, Applications

ATS Type	How It Works	Typical Applications
Open Transition	Disconnects the load from the utility power source before connecting it to the generator. This “break-before-make” approach results in a short, momentary power interruption ranging from milliseconds to a few seconds.	Non-critical commercial and light industrial settings where a brief outage will not cause harm or disrupt operations. Examples include office buildings and warehouses.
Closed Transition	Momentarily overlaps utility and generator power (“make-before-break”), ensuring seamless transfer and eliminating any power interruption during the switch.	Critical facilities such as hospitals, data centers, and process industries where even a split-second loss of power could compromise safety, equipment, or data integrity.
Static Transfer Switch (STS)	Uses solid-state electronics for ultra-fast switching between power sources, providing virtually instantaneous transfer without mechanical movement.	Applications with highly sensitive electronic loads, such as server rooms, telecom equipment, and mission-critical computing environments always requiring uninterrupted power.
Bypass‑isolation	Includes a manual bypass that lets you isolate the ATS for maintenance without interrupting power.	Emergency command centers and hospitals where maintenance must not disrupt critical power.

What Is Switchgear?

Switchgear refers to a collection of disconnect switches, fuses, relays, circuit breakers, and isolators used to control, protect and isolate electrical equipment. Switchgear is connected to electric supply systems and may operate at low, medium or high voltage.

Its primary purpose is to deenergize sections of a circuit for maintenance and to isolate faulty parts during a fault so that the rest of the system can continue operating. Examples of switchgear include industrial switchgear lineups and utility substation assemblies.

How Switchgear Works

In an automated protective scheme, a relay senses fault conditions such as short circuits or overloads. The relay then triggers a circuit breaker to open, isolating the faulty section and protecting the rest of the system. This quick isolation prevents equipment damage and maintains service continuity. Switchgear can also be operated manually, allowing maintenance personnel to isolate equipment safely.

Types of Switchgear

Switchgear is generally categorized by voltage:

Low‑voltage (LV) switchgear: Rated up to about 1 kV. LV switchgear includes breakers, isolators, earth leakage devices and fuses. It is commonly used in buildings and small industrial plants.
Medium‑voltage (MV) switchgear: Operates from 3 kV to 36 kV and may be metal‑enclosed indoor or outdoor types. MV switchgear uses air, oil or vacuum interrupters to break high fault currents.
High‑voltage (HV) switchgear: Rated above 36 kV, HV switchgear controls the transmission and distribution of large blocks of power at utilities. Gas‑insulated and hybrid designs allow for compact footprints and high reliability.

Benefits of Switchgear

Switchgear boosts system reliability by isolating faults and preventing cascaded outages. It responds quickly to abnormal conditions, provides manual control when necessary, and enables maintenance without shutting down entire systems. Because it separates functioning and non‑functioning parts, it ensures that critical loads remain energized during a fault.

ATS vs. Switchgear: A Detailed Comparison

The table below summarizes the key differences between an automatic transfer switch and switchgear. Understanding these distinctions will help you decide which device you need, or whether both are required.

Table: Automatic Transfer Switch Compared to Switchgear

Parameter	Automatic Transfer Switch (ATS)	Switchgear
Primary function	Automatically switches electrical load from the primary source to a backup generator during an outage and returns it when power is restored.	Controls, protects and isolates electrical circuits; manages power distribution and safeguards equipment from faults.
Operation	Uses microprocessor control to sense voltage/frequency and initiate generator startup; transfers load without human intervention.	Can be manual or automatic; includes breakers, fuses and relays that handle high voltages and fault currents.
Applications	Ensures uninterrupted power for critical facilities like hospitals, data centers and manufacturing plants. Also used in homes for backup power.	Distributes and protects circuits in commercial buildings, industrial plants and utility systems.
Components	Controller, sensing circuitry, switching mechanism (contactor, molded case or power frame), sometimes a bypass for maintenance.	Circuit breakers, fuses, relays, disconnects, protective relays, bus bars and insulation; may include meters and control logic.
Voltage & power handling	Typically handles low‑ to medium‑voltage loads and is designed for smooth transitions.	Manages low, medium and high voltages; capable of handling large fault currents.
Response time	Very fast, milliseconds to seconds; static transfer switches offer the quickest transfer.	Varies depending on relay and breaker settings; generally slower than static ATS devices.
Complexity	Generally simpler, focused on switching between sources.	More complex components that control, protect, isolate multiple circuits.
Maintenance	Requires regular testing but is often easier to maintain.	Requires more extensive maintenance and testing due to its critical protective function.

When Do You Need an ATS, Switchgear or Both?

In larger facilities with multiple feeders, high currents or critical operations, switchgear is indispensable. It distributes power to different circuits, provides short‑circuit and overload protection, and allows isolation for maintenance.

At the same time, an ATS ensures that power automatically transitions to a generator during an outage. In essence, the ATS handles source selection, while switchgear manages power distribution and protection. Modern standby systems integrate both components so that when the ATS switches sources, the switchgear seamlessly distributes power and protects equipment.

Integrating ATS and Switchgear

Proper integration between the ATS, switchgear and control systems enhances reliability and safety. Communication protocols (e.g., Modbus, Profibus or IoT standards) enable the ATS to coordinate with switchgear controllers. Electrical connections and cable runs must be designed to minimize voltage drop and allow clear signal paths.

System tests, including simulated outages and manual transfer tests, ensure that the ATS and switchgear interact correctly under various conditions. When retrofitting older equipment, compatibility and system complexity can pose challenges, so consult experienced engineers and consider modular or backwards‑compatible components.

Selecting the Right Equipment

When choosing an ATS or switchgear, consider:

Power requirements and load sensitivity: Determine whether your loads can tolerate brief interruptions (open transition) or require continuous power (closed or static transfer). Evaluate the total kVA/kW capacity and oversize the ATS and generator accordingly.
Number of generators and redundancy: Single‑generator systems are simpler, but multiple‑generator or parallel systems improve reliability. In multi‑building sites, each building may require its own ATS.
Voltage level and fault currents: Switchgear must be rated for the system voltage and short‑circuit current; choose low‑, medium‑ or high‑voltage gear as appropriate.
Environmental conditions: Consider indoor vs outdoor installation, temperature extremes, dust, humidity and corrosive environments. Choose switchgear with suitable insulation (air, gas or hybrid).
Budget and maintenance: Higher‑performance ATS (e.g., closed transition, static) and high‑voltage switchgear cost more upfront but reduce downtime and may lower long‑term costs. Factor in maintenance requirements for both devices.

For complex projects, consult with our specialists who can evaluate your facility’s needs and recommend the right combination of ATS and switchgear.

Next Steps

Automatic transfer switches and switchgear are both vital components of reliable standby power systems, but they perform very different roles. The ATS senses outages and commands a generator to restore power automatically; switchgear manages the safe distribution and protection of that power. Understanding the differences helps you choose the right equipment and design a system that meets your facility’s needs. If you’re planning a backup power project or upgrading an existing system, consult the experts at Depco Power Systems for personalized guidance.