An automatic transfer switch should be inspected and tested on a regular, documented schedule, but there is not one maintenance interval that applies to every ATS installation.
The appropriate frequency depends on the equipment manufacturer, facility type, applicable codes and standards, operating environment, load criticality and previous maintenance findings.
For emergency and standby power systems governed by NFPA 110, operational status inspections can be required weekly and transfer equipment is exercised as part of the monthly emergency-power-system testing program. Other commercial or industrial installations may follow different requirements based on the equipment and facility.
The safest approach is to establish a maintenance and testing program using the ATS manufacturer’s instructions, applicable facility requirements and the criticality of the connected load.
What Determines How Often an ATS Should Be Tested?
Automatic transfer switches do not all operate under the same conditions. A switch supporting a continuously operated critical facility may need a different maintenance program than equipment serving a less critical commercial load.
Manufacturer Recommendations
The ATS manufacturer’s inspection and maintenance instructions should be one of the primary references when developing a schedule.
Manufacturer procedures may address:
- Visual inspection
- Cleaning
- Electrical connections
- Contact condition
- Mechanical operation
- Controller operation
- Functional transfer testing
- Recommended service intervals
Some manufacturers also recommend more frequent inspection when equipment operates in dusty, dirty, humid or otherwise demanding environments.
Facility and Regulatory Requirements
Certain facilities are subject to specific emergency-power inspection and testing requirements.
For example, where NFPA 110 applies, the emergency power supply system and its associated components are inspected regularly and exercised under load on a defined schedule. Transfer switches are included within that emergency-power system.
For facilities governed by NFPA 110, this can include:
- Weekly operational-status inspections of the emergency power system and associated components
- Monthly exercise of the emergency power system under load
- Operation of transfer switches as part of the required testing program
- A documented maintenance and operational-testing schedule
These requirements should not be automatically applied to every ATS installation. The applicable code, adopted edition and facility requirements should be confirmed for the specific site.
Load Criticality
The consequences of ATS failure should also influence the maintenance program.
More frequent inspection or testing may be appropriate when the switch supports:
- Data center infrastructure
- Healthcare operations
- Emergency systems
- Industrial processes
- Communications equipment
- Other loads where an extended outage would create significant operational risk
In these environments, the ATS should be considered as part of the entire critical-power path rather than as an isolated component.
Operating Environment
Environmental conditions can affect inspection frequency.
Equipment exposed to conditions such as the following may warrant closer attention:
- Dust or airborne contamination
- Moisture
- Temperature extremes
- Corrosive environments
- Industrial contaminants
- Outdoor exposure
A clean, conditioned electrical room may present very different maintenance conditions from an industrial or outdoor installation.
Equipment Age and Condition
An older ATS or equipment with a history of problems may warrant more frequent inspection than a newer switch with consistent maintenance records and successful testing history.
Maintenance frequency may also need to increase when previous inspections identify:
- Contact deterioration
- Loose electrical connections
- Evidence of overheating
- Controller faults
- Mechanical wear
- Recurring alarms
- Inconsistent transfer operation
What Should Be Checked During ATS Inspection and Testing?
Inspection and functional testing serve different purposes and both can be important parts of an ATS maintenance program.
Routine Visual Inspection
A visual inspection can identify conditions that may require further investigation.
Items commonly reviewed include:
- Alarms and indicator status
- Controller display information
- Enclosure condition
- Dust or contamination
- Evidence of moisture
- Loose or damaged components
- Discoloration or signs of overheating
- Visible wiring condition
- Unusual equipment conditions
Preventative Maintenance
More detailed maintenance can include evaluating electrical and mechanical components according to the manufacturer’s procedures.
This may include:
- Checking electrical connections
- Inspecting for evidence of overheating
- Evaluating contact erosion or wear
- Removing accumulated dust and dirt
- Inspecting mechanical operation
- Reviewing controller settings and alarms
- Replacing serviceable components when required
For a more complete discussion, see Automatic Transfer Switch Maintenance: Inspection, Testing & Replacement Considerations.
Functional Transfer Testing
A visual inspection cannot confirm that the ATS will successfully perform its complete transfer sequence.
A functional test may verify whether the system can:
- Detect unacceptable normal-source conditions
- Initiate the alternate power source when required
- Recognize acceptable alternate-source power
- Transfer the connected load
- Maintain the load on the alternate source
- Recognize restoration of normal power
- Retransfer the load correctly
- Complete the required cooldown or shutdown sequence
The test procedure should be coordinated with the facility before initiating a transfer, especially when critical loads are involved.
When Should an ATS Be Tested Outside the Normal Schedule?
Additional inspection or testing may be appropriate when something has changed or a potential problem has been identified.
Examples include:
- After ATS maintenance or repair
- After replacement of major components
- Following a failed or incomplete transfer
- After an unexpected alarm or controller fault
- Following electrical-system modifications
- After generator or source changes
- When facility load requirements change significantly
- When overheating or abnormal equipment conditions are discovered
Testing after maintenance or repair can help confirm that the transfer equipment and associated emergency-power components operate as intended before the system is returned to normal service.
What If the ATS Does Not Pass Testing?
A failed test does not automatically mean the complete automatic transfer switch needs to be replaced.
The cause should first be identified. Depending on the problem, corrective work may involve:
- Controller adjustments
- Electrical connection repairs
- Mechanical service
- Contact or component replacement
- Source-sensing corrections
- Generator-start circuit troubleshooting
- Repair of other associated electrical equipment
If problems are recurring, critical parts are obsolete, or the ATS no longer meets the facility’s electrical requirements, replacement may need to be evaluated.
Use the Automatic Transfer Switch Sizing Guide when evaluating replacement equipment.
Does a Bypass-Isolation ATS Make Maintenance Easier?
It can.
A bypass-isolation automatic transfer switch provides an alternate switching path that can allow the primary ATS mechanism to be isolated for certain inspection, testing or maintenance activities while maintaining a power path to the protected load.
This capability can be particularly useful in facilities where taking the ATS completely out of service is difficult.
Learn more in What Is a Bypass-Isolation Automatic Transfer Switch and When Is It Used?
Do Service-Entrance Transfer Switches Need Different Planning?
Service-entrance-rated ATS equipment still requires inspection and testing, but its position within the electrical service can affect how maintenance and outages are planned.
Service disconnecting, grounding, bonding, available fault current and other electrical-system requirements should be considered before maintenance or replacement work is performed.
See What Is a Service-Entrance-Rated Automatic Transfer Switch? for additional information.
Need ATS Inspection, Testing or Maintenance?
A documented ATS inspection and testing program can help identify developing problems before the equipment is required during an actual utility outage.
CI Group provides Automatic Transfer Switch Service & Maintenance for existing commercial, industrial and critical-power equipment.
If testing determines that replacement should be considered, browse CI Group’s Automatic Transfer Switch inventory and use the appropriate electrical and amperage requirements to narrow available equipment.