Power cannot wait for someone to arrive and switch manually
Hospitals, shopping centers, hotels, data centers and unmanned facilities need the system to take over under predefined conditions.
Power-System Component / Critical-Load Takeover
Automatic Transfer Switch Systems
A standby generator starting does not mean critical loads have recovered. The ATS senses the utility source, issues the generator start command, verifies a stable alternate source, transfers the load and returns it after utility recovery. It determines whether power actually reaches the circuits that need it.
100A–3200AAutomatic / Manual TransferMechanical and Electrical InterlockingCritical-Load Segmentation
Why an ATS Is Needed
When critical loads must transfer without waiting for personnel, the transfer sequence belongs in the complete standby-power design
The value is not merely an automatic cabinet. It turns outage detection, generator start, load transfer, fault lockout and utility return into a testable and repeatable operating process.
Critical loads must enter standby power by priority
Fire systems, security, pumps, UPS and controls require a clear plan for what returns first, what is delayed and what should remain disconnected.
A generator exists, but no clear low-voltage single-line diagram is available
Without defined utility incomer, busbar, critical circuits and protection boundaries, even a large ATS may transfer the wrong load.
The mechanism's transfer time is mistaken for the total outage duration
Actual interruption also includes source-failure detection, generator starting and stabilization delays. Sensitive loads generally require a UPS across this window.
Complete Path from Outage to Recovery
The ATS works with generator controls, low-voltage distribution and the load-restoration sequence
Every step needs a state, delay and failure response. Timing should follow site risk rather than applying one fixed delay set to every project.
Utility failure, undervoltage or abnormal source
Monitor three-phase voltage and phase loss, then use a delay to distinguish an outage from a momentary disturbance.
Issue the generator start signal
The generator controller executes the start cycle while monitoring fail-to-start, battery, oil pressure and set alarms.
Verify generator voltage and frequency
The ATS only permits transfer after the source reaches acceptable conditions and any warm-up delay has elapsed.
Disconnect utility and connect generator
Mechanical and electrical interlocks prevent unintended source paralleling, while position feedback confirms the actual state.
Confirm utility has recovered and remains stable
After a return delay, the load transfers back to utility without repeated operation during a brief recovery.
Cool down, stop and return to standby
The generator runs unloaded for cooldown before stopping, while events, alarms and transfer records remain available for review.
Configuration Range
From a standalone source-transfer cabinet to generator-integrated controls, choose the arrangement around current and installation boundaries
An ATS may be a standalone cabinet, part of the generator control package or integrated into a low-voltage switchboard lineup. Define the connection point before selecting the enclosure format.
Automatic Dual-Source Transfer Cabinet
Utility, generator and load enter separately, allowing flexible combination with existing sets and low-voltage boards and more freedom for cable entry.
Integrated Automatic ATS Cabinet
Combines generator start/stop control, source transfer and status indication for straightforward single-set projects.
Enclosure- or Generator-Side Integration
Places the ATS near the set where space is limited, while cable routes, service access, protection and load-side interfaces still require review.
Transfer Unit Coordinated with Low-Voltage Switchgear
For large-current or multi-zone projects, coordinating incomers, bus couplers, critical busbars, selective protection and future expansion.
If maintenance without interruption or special operating modes are required, bypass, temporary-source or multi-source transfer arrangements must be defined separately. These functions should not be assumed in a standard two-source ATS.
Rated Current and Critical Parameters
100A–3200A defines a current range; six electrical conditions determine whether the system can transfer reliably
ATS selection follows current and system fault conditions, not a simple conversion from generator kW to a switch model. Protection, cables and neutral treatment must be reviewed together.
100–400ASmaller critical-load zones or individual systems, with starting current and upstream protection checked.
400–1000AMedium commercial critical busbars where cable quantity, entry space and heat dissipation require review.
1000–2000ALarger load zones requiring project-specific busbar, enclosure, short-circuit withstand and protection coordination.
2000–3200ALarge-current switchboard lineups requiring dedicated transport, installation, bus connection, temperature-rise and service-space review.
3-Pole / 4-PoleSelected around neutral switching, grounding arrangement and local requirements
Automatic / Manual ModesManual operation requires clear authorization, interlocking and position indication
Transfer TimeReference data may show 0.6s, 1.2s or 2.4s; final timing follows the mechanism
Open-Transition LogicBreak before make; sources must not connect together without synchronization
Short-Circuit Withstand and ProtectionCoordinated with upstream breakers, downstream cables and available fault current
Controls and CommunicationsStatus, alarms, remote signals and BMS/monitoring interfaces confirmed by project
Cabinet Design and Customer Value
Long-term reliability depends on whether the transfer mechanism, interlocks, busbars and control wiring can be verified
Customers do not need to design the ATS, but they should see the main electrical areas, service clearances and test method before delivery.
Dual-Source Transfer Mechanism
Current rating, pole count and operating life must suit load current and expected transfer frequency.
Mechanical and Electrical Interlocks
Two independent constraints prevent utility and generator from connecting together without synchronization.
Busbars, Terminals and Phase Sequence
Busbar section, connection torque, insulation clearances and phase identification affect temperature rise and correct cabling.
Controller and Source Sensing
Monitors both sources and executes delays, start, transfer, return and fault-lockout logic.
Automatic and Manual Operation
Mode selection, permissions and emergency procedures should be clear to prevent unintended operation during maintenance.
Position and Alarm Indication
Local and remote signals should distinguish utility position, generator position, fault and incomplete transfer.
Cable Entry and Service Space
Allow room for cable bending, termination, thermography, tightening and transfer-mechanism replacement.
Testing and Event Records
No-load, load, source-failure, return and fault tests should create traceable records.
Six Project Inputs
Define sources, loads and allowable interruption before quotation so the ATS becomes an executable takeover plan
Utility and generator capacity
Provide voltage, frequency, phases, rated current, grounding arrangement and available capacity for both sources.
Critical circuits and restoration priority
List fire systems, security, pumps, elevators, UPS, controls and general loads, and identify what must transfer.
Allowable interruption and UPS ride-through
Separate millisecond, second-level and delayable loads, and confirm whether the UPS covers generator start and transfer.
Single-line diagram, switchboard and cables
Provide the existing low-voltage single-line, cable-entry direction, fault level, protection, cabinet location and service space.
Starting, return and system interlocks
Confirm delays, auto/manual modes, fire-system signals, load shedding, remote signals and fail-safe position.
Test frequency and record ownership
Define who performs simulated outage, loaded transfer, return, alarm and maintenance tests, and how records are retained.
Typical Transfer Tasks
The same ATS serves very different loads and time windows in different facilities
Use the UPS across the start window and the ATS for sustained source takeover
Hospital IT, medical equipment and data-center IT require UPS continuity; the ATS delivers stable generator power to the UPS and cooling auxiliaries.
Restore fire, security, emergency lighting and essential pumps first
Shopping centers, hotels and schools divide critical circuits by regulation and operational risk so general loads do not consume standby capacity.
Stage large motor recovery to avoid overloading the generator again
Factories and large facilities can delay loads by priority, starting method and process sequence to reduce a second shutdown after transfer.
Review the ATS configuration around critical loads and allowable interruption
Share utility and generator capacity, critical-load list, allowable interruption, UPS ride-through, single-line diagram, cabinet location and interlock requirements. HOHANK engineers will define current rating, pole count, controls and distribution boundary.