An automatic transfer switch may remain in the same operating position for long periods of time, yet it is expected to respond correctly when normal power becomes unavailable. That makes inspection, testing and preventative maintenance an important part of maintaining a reliable backup-power system.
Automatic transfer switch maintenance should evaluate more than whether the ATS can move from one source to another. Electrical connections, contacts, controls, sensing, mechanical operation, environmental conditions and the overall condition of the equipment can all affect performance.
For facilities maintaining existing transfer equipment, CI Group provides Automatic Transfer Switch Service & Maintenance for commercial, industrial and critical-power applications.
Why Automatic Transfer Switch Maintenance Matters
An automatic transfer switch connects the protected load to the appropriate available power source. When normal power is interrupted or falls outside acceptable conditions, the ATS works with the alternate power system to transfer the designated load.
Because the transfer switch sits directly in that critical power path, a functioning generator alone does not guarantee that the protected load will successfully receive backup power.
ATS reliability can be affected by conditions such as:
- Loose or deteriorated electrical connections
- Contact wear or erosion
- Evidence of overheating
- Dust, dirt or contamination
- Mechanical wear or binding
- Controller or sensing issues
- Incorrect or outdated settings
- Moisture, corrosion or environmental exposure
- Changes to the facility’s electrical system
- Equipment age and parts availability
Routine inspection and functional testing can help identify developing problems before the transfer switch is required during an actual power interruption.
What Should Automatic Transfer Switch Maintenance Evaluate?
The exact maintenance procedure depends on the ATS manufacturer, model, configuration, application and facility requirements. Manufacturer instructions and applicable electrical-safety procedures should always be followed.
As part of a broader maintenance program, the following areas commonly deserve evaluation.
1. General Equipment Condition
A visual inspection can identify conditions that may indicate deterioration or a developing electrical or mechanical problem.
Items that may warrant attention include:
- Condition of the enclosure
- Signs of moisture entry
- Dust or contamination
- Corrosion
- Discoloration
- Signs of overheating
- Damaged wiring or insulation
- Loose or damaged components
- Evidence of arcing or carbon tracking
- Unusual odors or visible heat damage
The installation environment should also be considered. Transfer switches installed outdoors, in industrial spaces or in areas exposed to dust, moisture or temperature extremes may require different maintenance attention than equipment installed in a clean, conditioned electrical room.
2. Electrical Connections
Connections on the normal source, alternate source and load side are important parts of ATS reliability.
Loose or deteriorated connections can contribute to resistance, excessive heat and equipment damage. Control wiring and other accessible terminations should also be evaluated according to the manufacturer’s service procedures.
Signs of overheating should be investigated rather than treated only as a cosmetic issue because the underlying cause may involve a connection, contact, loading or other electrical problem.
3. Transfer-Switch Contacts
The main switching contacts carry the facility load and are subject to mechanical and electrical wear.
Depending on the equipment design, maintenance may include evaluating accessible contacts for:
- Excessive erosion
- Pitting
- Overheating
- Contamination
- Abnormal wear
- Mechanical damage
Contact condition should be evaluated against the manufacturer’s criteria. Visible wear does not automatically mean the complete transfer switch needs to be replaced, but significant deterioration may require service or component replacement.
4. Mechanical Operation
The mechanical transfer mechanism needs to operate freely and correctly when the ATS changes sources.
Inspection may include the condition and operation of:
- Mechanical linkages
- Operating mechanisms
- Interlocks
- Position indicators
- Moving components
- Bypass or isolation mechanisms, where equipped
Binding, abnormal resistance, inconsistent operation or unusual mechanical noise should be investigated before the equipment is relied upon during an outage.
5. ATS Controller and Source Sensing
Modern automatic transfer switches rely on controllers to monitor the normal and alternate sources and determine when transfer and retransfer should occur.
Depending on the equipment, maintenance and testing may include reviewing:
- Active alarms
- Event or fault history
- Normal-source sensing
- Alternate-source sensing
- Voltage and frequency parameters
- Transfer delays
- Retransfer delays
- Engine-start signals
- Exercise settings
- Control power
- Communication or monitoring functions
An ATS can be mechanically sound but still fail to perform correctly if the sensing, controller or operating settings do not respond as intended.
Functional Testing Is Different From a Visual Inspection
A visual inspection can identify many physical problems, but it cannot confirm that the entire transfer sequence will work correctly.
Functional testing evaluates whether the ATS responds appropriately when normal and alternate source conditions change.
Depending on the facility and system design, a transfer test may evaluate whether the system can:
- Recognize loss or unacceptable normal power
- Send the required generator-start signal
- Recognize when the alternate source is acceptable
- Transfer the load to the alternate source
- Maintain the required load on the alternate source
- Recognize restoration of normal power
- Retransfer the load correctly
- Complete the appropriate generator cooldown sequence
Testing should be planned around the specific facility and connected load. Critical facilities may need additional coordination before a live transfer test is performed.
For a focused discussion of inspection and testing schedules, see How Often Should an Automatic Transfer Switch Be Inspected and Tested?
How Often Should an ATS Be Inspected and Tested?
There is not one maintenance interval that should be applied to every ATS without considering the equipment and application.
The appropriate inspection, maintenance and testing program can depend on:
- Manufacturer recommendations
- Facility type
- Applicable codes and standards
- Load criticality
- Operating environment
- Equipment age
- Previous maintenance findings
- Transfer frequency
- Facility operating procedures
Rather than treating one generic schedule as appropriate for every installation, facilities should establish a documented maintenance and testing program based on their actual equipment and operating requirements.
Read How Often Should an Automatic Transfer Switch Be Inspected and Tested? for additional guidance on this specific question.
Common Signs an ATS May Need Service
Not every transfer-switch problem means the ATS needs to be replaced.
Some conditions can be addressed through testing, adjustment, repair or replacement of serviceable components.
Conditions that should be investigated may include:
- Failure during an operational transfer test
- Intermittent or inconsistent transfer operation
- Unexpected alarms
- Controller faults
- Source-sensing problems
- Incorrect transfer or retransfer timing
- Mechanical binding
- Loose electrical connections
- Evidence of overheating
- Deteriorated contacts
- Failure to initiate the alternate power source
- Incorrect switch-position indication
- Communication or monitoring failures
The underlying cause should be identified before deciding whether the appropriate response is adjustment, maintenance, repair or replacement.
For facilities experiencing ATS problems, CI Group’s Automatic Transfer Switch Service & Maintenance page outlines available service support.
When Should Automatic Transfer Switch Replacement Be Considered?
There is no universal age at which every automatic transfer switch must be replaced.
Replacement planning should consider the actual condition of the equipment, its reliability, whether parts and technical support remain available, and whether the ATS still meets the facility’s electrical and operational requirements.
Replacement may warrant evaluation when:
- The ATS repeatedly fails testing
- Mechanical operation has become unreliable
- Contacts or major switching components show significant deterioration
- Critical replacement parts are unavailable
- The controller has become obsolete or unsupported
- Repairs are becoming frequent
- The facility’s load has increased beyond the existing equipment requirements
- Voltage or electrical configuration has changed
- A different pole or neutral arrangement is required
- The facility requires a different transfer type
- Service-entrance requirements have changed
- Bypass-isolation capability is now needed
- Expansion has changed the overall critical-power architecture
If replacement is being considered, the new ATS should be evaluated against the facility’s current requirements rather than automatically duplicating the specifications of the existing equipment.
Use the Automatic Transfer Switch Sizing Guide: Amperage, Voltage, Poles & Application Requirements to review the primary selection factors before sourcing replacement equipment.
Maintenance, Repair or Replacement?
The appropriate path depends on both equipment condition and the requirements of the electrical system.
Maintenance May Be Appropriate When:
- The ATS operates correctly during testing
- Routine service items can be addressed
- Electrical ratings still match the application
- The controller and major components remain supported
- Parts remain available
- No significant reliability problems have developed
Repair May Be Appropriate When:
- A specific serviceable component has failed
- The underlying switching equipment remains in usable condition
- Replacement components remain available
- The repair can restore reliable operation
- The existing electrical configuration still meets facility requirements
Replacement May Be Appropriate When:
- Reliability problems are recurring
- Major components are deteriorated or obsolete
- Parts or technical support are no longer readily available
- The ATS no longer matches the facility load or electrical configuration
- The facility requires capabilities the existing equipment does not provide
The decision should consider the complete system rather than the age of the ATS alone.
Bypass-Isolation Can Change the Maintenance Strategy
One challenge with maintaining an automatic transfer switch is that the equipment may be carrying an important facility load.
For applications where taking the primary ATS completely out of service would create unacceptable operational risk, a bypass-isolation transfer switch may provide additional maintenance flexibility.
A bypass-isolation configuration provides an alternate path that can allow the transfer mechanism to be isolated for certain service activities while the load remains supported through the bypass arrangement.
This configuration is particularly relevant where maintainability and continuity are major design considerations.
Learn more in What Is a Bypass-Isolation Automatic Transfer Switch and When Is It Used?
Service-Entrance ATS Replacement Requires Additional Planning
If the transfer switch is located at the electrical service entrance, replacement planning needs to account for the ATS’s role as service equipment.
Project requirements can include:
- Service-entrance rating
- Disconnecting requirements
- Overcurrent protection
- Grounding and bonding
- Available fault current
- Required amperage
- System voltage
- Applicable electrical requirements
See What Is a Service-Entrance-Rated Automatic Transfer Switch? for a more focused explanation.
Consider the Existing Manufacturer and ATS Family
When replacement equipment is being evaluated, the existing manufacturer and product family can provide useful information, but the series name alone should not determine the replacement.
Document the existing:
- Manufacturer
- Series and model
- Amperage
- Voltage
- Phase
- Number of poles
- Transfer type
- Controller
- Enclosure
- Service-entrance configuration
- Bypass-isolation configuration, if applicable
For facilities evaluating ASCO equipment, see ASCO 7000 Series vs. ASCO 300 Series Automatic Transfer Switches for a comparison of the two product families.
ATS Maintenance in Data Center and Critical-Power Environments
In a data center or other critical-power facility, the transfer switch should be considered as part of the complete power path rather than as an isolated piece of equipment.
Maintenance planning may need to coordinate the ATS with:
- UPS systems
- Backup generators
- Electrical distribution
- Switchgear
- Redundant power paths
- Temporary power requirements
- Facility maintenance windows
CI Group’s Data Center Power Infrastructure & Critical Equipment page provides additional information about coordinating these systems in larger critical-power environments.
Replacing an ATS? Browse Equipment by Amperage
When maintenance findings indicate that replacement should be considered, amperage is one of the first specifications used to narrow available equipment.
CI Group organizes automatic transfer switch inventory into five capacity ranges:
- 0–260A Automatic Transfer Switches
- 261–800A Automatic Transfer Switches
- 801–1600A Automatic Transfer Switches
- 1601–3000A Automatic Transfer Switches
- 3001+A Automatic Transfer Switches
After identifying the required amperage range, replacement equipment should still be evaluated for voltage, phase, number of poles, transfer type, service-entrance requirements, enclosure, fault-current requirements and other application-specific specifications.
For a full review of those factors, see the Automatic Transfer Switch Sizing Guide.
Automatic Transfer Switch Maintenance Checklist
A documented ATS maintenance program can help facilities track equipment condition and identify changes over time.
Equipment Information
- Manufacturer
- Series and model
- Amperage
- Voltage and phase
- Number of poles
- Transfer type
- Controller
- Service-entrance or bypass-isolation configuration
Inspection Considerations
- Enclosure and environmental condition
- Electrical connections
- Evidence of overheating
- Contact condition
- Dust or contamination
- Mechanical condition
- Wiring condition
- Controller alarms and event history
Functional Testing Considerations
- Normal-source sensing
- Alternate-source sensing
- Generator-start signal
- Transfer operation
- Retransfer operation
- Time-delay operation
- Position indication
- Generator cooldown sequence
Follow-Up
- Document identified deficiencies
- Determine whether adjustment or repair is required
- Confirm parts availability
- Track recurring problems
- Evaluate whether replacement planning is appropriate
Related Automatic Transfer Switch Resources
Automatic Transfer Switch Sizing Guide: Amperage, Voltage, Poles & Application Requirements
Review amperage, voltage, poles, fault-current requirements and application factors before selecting ATS equipment.
ASCO 7000 Series vs. ASCO 300 Series Automatic Transfer Switches
Compare two major ASCO ATS families and the applications and configurations each is designed to support.
How Often Should an Automatic Transfer Switch Be Inspected and Tested?
Learn what can affect the appropriate inspection and testing schedule for ATS equipment.
What Is a Bypass-Isolation Automatic Transfer Switch and When Is It Used?
Learn how bypass-isolation equipment can provide additional maintenance flexibility in critical-power applications.
What Is a Service-Entrance-Rated Automatic Transfer Switch?
Understand how ATS location at the electrical service affects equipment requirements.
Need Automatic Transfer Switch Service or Replacement Support?
Automatic transfer switch maintenance should help determine whether the equipment remains mechanically, electrically and operationally capable of supporting the facility’s power requirements.
If inspection or testing identifies a problem, the appropriate next step may involve adjustment, repair, component replacement or planning for a replacement ATS depending on the condition and supportability of the existing equipment.
Request Automatic Transfer Switch Service & Maintenance
If replacement equipment is being considered, browse CI Group’s Automatic Transfer Switch inventory and use the appropriate amperage category to narrow available equipment.