Identity
Nameplate, model, serial, rating, poles, voltage/frequency, controller and asset ID.
Automatic transfer switch maintenance control
27-Point ATS Maintenance Checklist (With Torque & Test Specs)
A model-aware, recordable program for qualified electrical maintenance teams—covering identity, de-energized inspection, source logic, approved functional testing, deficiencies and the final as-left state.
“With specs” means traceable specification fields—not universal numbers. Enter torque, test stimulus, thresholds, timing and acceptance criteria only from the exact ATS documentation and approved site plan.
27 traceable checkpointsFive controlled phases from identity to as-left verification.
Six specification recordsAsset, documents, torque, function, electrical test and final state.
Four honest statusesPass, Fail, N.A. and Deferred—blank never means pass.
Zero generic valuesNo guessed torque, test voltage, thresholds, timing or intervals.
Controlled relay testing illustrates documentation and test discipline; it is not an ATS procedure or live-work authorization. Photo: MTA Capital Construction Mega Projects / Wikimedia Commons, CC BY 2.0. Cropped and darkened.
Direct answer
Use the checklist as a controlled record system—not a generic service recipe
Start by identifying the exact automatic transfer switch, its controller, transition type, sources and approved documents. Separate work that requires an established de-energized condition from a planned functional transfer test. For every torque or electrical test point, record the authoritative source, required method, tool or instrument, acceptance criterion and result.
Do not copy a value from another frame, another terminal, an internet chart or a previous project. If the exact criterion is missing, stop that task and record Deferred. The checklist can still document safe progress without pretending an unverified item passed.
The maintenance record must answer three questions.
What exact asset and revision were inspected? What approved evidence defined pass or fail? What source, controller, generator and bypass/isolation state was left for operations?
Planning and documentation only. This page is not a switching sequence, wiring guide, energized-work justification, LOTO procedure, bypass/isolation operating instruction or permission to open an ATS.
Authority
Current applicable OEM documents, one-line, wiring, settings, site procedure and verifier.
Evidence
Exact point, method, tool/instrument, calibration, criterion, reading, photographs and timestamps.
Handoff
Defects, owner, risk, due date, retest, as-left state, independent check and acceptance.
Multiple-source safety boundary
An ATS can remain hazardous after one source is opened
Utility, generator, control power, remote start circuits, stored-energy mechanisms, batteries and bypass/isolation paths can cross the work boundary. Controller selectors, test switches, interlocks and displayed status are not substitutes for energy-isolating devices and verified absence of voltage.
For U.S. general-industry work, the facility should evaluate electrical exposure under OSHA Subpart S, including 29 CFR 1910.333. The broader hazardous-energy program in 29 CFR 1910.147 may also apply to unexpected start-up, stored energy and related scope, but it is not the sole electrical-work reference.
- Identify qualified roles, operating authority, communication and stop-work ownership before the job.
- Control every relevant source under the site procedure and exact equipment arrangement.
- Use correctly rated test equipment and the employer's approved verification method.
- Re-establish controls after any approved test or positioning step before intrusive work resumes.
- Keep critical-load stakeholders and generator operators inside the functional-test plan.
Do not rely on an LED, HMI icon or selector position to prove de-energization. Use the site electrical-safety program, the exact one-line and a qualified person's verification.
Why values are model-specific
There is no universal ATS torque or test value
A valid number belongs to an exact point, construction, conductor or hardware condition, document revision, test method and acceptance rule. A correct value in the wrong context is still wrong.
Identify before acting
Source/load/neutral/ground lug, bus joint, terminal block and mechanism fastener can have different instructions.
Record location, hardware, conductor, value, units, preparation, document page and calibrated tool.Do not disturb by habit
A maintenance torque check is not automatically the same as the installation torque procedure.
Do not re-torque unless the exact OEM maintenance procedure requires it.Protect connected electronics
Test voltage, isolation, disconnected components, instrument rating and pass criterion depend on the installed design.
Do not apply an unsanctioned dielectric or insulation-resistance test.Use the approved program
Source thresholds, delays, transition behavior and maintenance frequency vary by controller, system duty and governing program.
Use OEM, site, legal/insurance, risk, environment and duty history—not a generic calendar.Before-work control sheet
Capture six records before a wrench, probe or transfer test
Each card has a before-work input and an after-work evidence package. Treat missing inputs as a hold point.
Exact asset configuration
Before: manufacturer, model/MPN, serial, amperes, poles, voltage/frequency, transition type, controller and firmware if shown.
After: nameplate photo/reference, drawing reference and work-order asset ID.Applicable controlled information
Before: OEM O&M/installation/service manual, rating label, one-line, wiring, approved settings and site procedure.
After: title, number, revision/date, page/figure/table and verifier.Connection-specific authority
Before: exact location plus hardware and conductor identity; confirm whether the approved maintenance method calls for torque action.
After: published value/units, preparation, tool ID/calibration, technician and date.Scenario and abort criteria
Before: approved scenario, source/load state, outage constraints, expected sequence, programmed delays and stop conditions.
After: start/end, sequence, required timing, alarms, load impact and pass/fail.Method and acceptance
Before: approved method, isolation, stimulus/test voltage if specified, instrument category/rating/calibration and criterion.
After: test points, readings, relevant ambient condition, result and reviewer.Operations handoff
Before: required source, controller mode, bypass/isolation position, generator mode, alarms, covers and labels.
After: independent verification, open defects, owner acceptance and next due date.The complete recordable program
The 27-point ATS maintenance checklist
Five groups preserve the work sequence without turning the page into a switching procedure. For each line, attach objective evidence and choose Pass, Fail, N.A. or Deferred.
5A. Pre-job controlIdentity, documents, scope, roles and baseline.
8B. Physical conditionEnclosure, conductors, mechanism, torque control and controller record.
5C. Sources and logicSensing, control power, interfaces and approved settings.
6D. Functional testReadiness, transfer, return, bypass, alarms and source behavior.
3E. Close-outElectrical-test traceability, defects and as-left state.
A
Pre-job control and equipment identity
Resolve scope, authority and baseline discrepancies before maintenance or testing begins.
Points 01–05
Confirm the exact ATS asset from the nameplate and work order.
Capture: manufacturer, model, serial, rating, pole count, voltage/frequency and controller. Resolve every mismatch before work.
StatusPass / Fail / N.A. / Deferred
Collect the applicable OEM documents, rating data, one-line, wiring and approved settings record.
Evidence: document number, revision/date and relevant page, table or figure entered in the control sheet.
StatusPass / Fail / N.A. / Deferred
Review the approved scope, outage/load plan, generator readiness, bypass implications and critical constraints.
Evidence: responsible operator, authority to proceed, hold points and abort criteria are named.
StatusPass / Fail / N.A. / Deferred
Confirm qualified people, roles, communication, task risk assessment, PPE and energy-control procedure.
Evidence: team briefing and authorization are documented under the site program.
StatusPass / Fail / N.A. / Deferred
Capture the as-found controller, alarms, events, sources, load position, communications and indications.
Evidence: baseline log, export or photographs attached; unexplained alarms escalated before testing.
StatusPass / Fail / N.A. / Deferred
Evidence before action
A label, wire and setting must remain tied to the same asset revision
Photographs and exports are useful only when they can be traced to the exact ATS, work order and document revision. Record discrepancies rather than normalizing them in the field.
- Photograph the nameplate and asset identifier before covers or labels are moved.
- Use wire and terminal designations from the approved drawing, not an assumed color code.
- Preserve the as-found controller settings and event log before authorized changes.
- Pair every torque entry with the exact connection and tool calibration record.
- Make the evidence understandable to a second qualified reviewer.
Good evidence is reproducible.
Another reviewer should be able to identify what was inspected, which requirement applied and why the status was assigned.
B
Physical condition and controlled controller review
Intrusive visual/mechanical work is de-energized under the approved procedure. Controller data is reviewed only in the OEM- and site-permitted condition.
Points 06–13
Inspect enclosure, access, ventilation, labels, doors, gaskets, contamination, moisture, pests and modifications.
Accept when: safe access, cooling, identification and environmental suitability are not compromised.
StatusPass / Fail / N.A. / Deferred
Look for heat damage, discoloration, arcing evidence, odor, corrosion, tracking, debris, insulation damage or abnormal wear.
Evidence: suspected thermal or arcing conditions are photographed and evaluated before return to service.
StatusPass / Fail / N.A. / Deferred
Inspect mechanism, linkages, interlocks, shutters and maintenance-handle storage only as the OEM procedure permits.
Accept when: no binding, damage, obstruction or missing part exists; no manual operation occurs outside the approved condition.
StatusPass / Fail / N.A. / Deferred
Inspect source, load, neutral and grounding conductors for routing, strain, engagement, insulation, identification and heat signs.
Accept when: condition agrees with drawings and labels and shows no damage or abnormal heating evidence.
StatusPass / Fail / N.A. / Deferred
Create a connection-by-connection torque control record before any approved torque action.
Record: point, source document, value/units, preparation and calibrated tool. Never use memory or a generic chart; do not re-torque an in-service connection unless the exact OEM maintenance procedure requires it.
StatusPass / Fail / N.A. / Deferred
Confirm bonding/grounding and switched- or solid-neutral arrangement against the one-line and OEM drawings.
Accept when: configuration matches the approved design. Escalate discrepancies; do not field-correct by guesswork.
StatusPass / Fail / N.A. / Deferred
Inspect control wiring, terminal blocks, fuses, relays, harnesses, connectors and shielding.
Accept when: labeling, condition, separation and retention agree with approved drawings and no part is loose, damaged or heat affected.
StatusPass / Fail / N.A. / Deferred
Review controller/display, time/date, communications, event memory and retention arrangement in the permitted condition.
Evidence: data is readable and backed up where available; configuration changes remain prohibited unless formally authorized.
StatusPass / Fail / N.A. / Deferred
C
Sources, controls and programmed logic
Verify what the installed system reports, then compare it with the approved cause-and-effect and settings record.
Points 14–18
Verify normal-source sensing, indication and associated protection with the approved method.
Accept when: displayed status agrees with the actual source condition and approved settings record.
StatusPass / Fail / N.A. / Deferred
Verify emergency-source sensing, indication, generator-start interface and associated protection.
Accept when: displayed status agrees with the actual source condition and approved settings record.
StatusPass / Fail / N.A. / Deferred
Inspect control power, charger, battery/start circuit and controller retention where installed and inside the assigned asset boundary.
Accept when: condition, alarms and readings meet the responsible equipment/system manufacturer's criteria.
StatusPass / Fail / N.A. / Deferred
Verify auxiliary contacts, permissives, inhibit inputs, remote controls and protective interlocks.
Evidence: actual I/O agrees with approved wiring and cause-and-effect; no defeated interlock or unexplained state remains.
StatusPass / Fail / N.A. / Deferred
Compare delays, cooldown, source windows, transition mode, in-phase/closed-transition options and load-shed logic.
Evidence: actual settings and their source document are recorded. Any change requires authorization, backup and a re-test plan.
StatusPass / Fail / N.A. / Deferred
Configuration control
The installed ATS—not the article title—defines the test
Two products sold as automatic transfer switches can use different mechanisms, transition modes, controller logic, neutral arrangements, bypass/isolation features, sensing architecture and maintenance access. Even a manual from the same brand can be wrong for another frame or revision.
- Match the complete catalog or model number, serial and controller—not only the ampere rating.
- Confirm whether the document is current for that asset; a legacy manual can be correct for legacy equipment but not a current family.
- Record transition type and any closed-transition or in-phase function before planning source simulation.
- Define which charger, battery, generator-start and remote-monitoring components belong to the ATS work scope.
- Escalate missing pages, illegible labels, field modifications and undocumented firmware before testing.
Controller settings are operational protection data. Routine maintenance compares them with the approved record; it does not authorize “tuning” thresholds, delays or source windows.
Approved functional testing
Five gates before the first test event
A functional test intentionally changes system state. It needs operational ownership, expected behavior and stop conditions—not an improvised “simulate failure” instruction.
GATE 01Define the starting stateSources, ATS position, controller mode, generator and bypass/isolation.
GATE 02Approve load impactCritical-load owner, outage window, downstream effects and communications.
GATE 03Name the directorOne person controls test progression, observations and abort authority.
GATE 04Freeze criteriaOEM method, approved settings, expected sequence, timings and alarms.
GATE 05Prepare restorationRequired as-left state, independent check, notifications and defect path.
No universal transfer threshold applies here. Pickup/dropout values, delays, synchronization windows, overlap limits, test stimuli and acceptable interruptions remain traceable to the installed controller and approved system criteria.
Field execution boundary
Qualified work still needs site-specific authority
A photograph can illustrate professional field work, but it cannot prove the pictured method, PPE, isolation, equipment rating or sequence is suitable for another ATS. The approved procedure and exact equipment documentation remain controlling.
- Before: confirm source and load states, people, communications, generator readiness and stop conditions.
- During: record events without bypassing an interlock, defeating protection or probing an unapproved point.
- After: verify source, controller, generator and bypass/isolation state independently.
- If unexpected: use the pre-agreed abort path, preserve evidence and classify the item Fail or Deferred.
Appearance is not authorization. This checklist deliberately omits remote switching instructions and invasive live-test steps.
D
Functional testing under an approved site plan
Observe only the authorized sequence and exact equipment criteria; preserve load safety and a controlled abort path.
Points 19–24
Hold the pre-test readiness check.
Record: source/load starting state, personnel locations, critical-load approval, communications, generator readiness, abort criteria, named test director, ATS position and controller mode.
StatusPass / Fail / N.A. / Deferred
Perform the approved normal-to-emergency functional sequence with the installed controller/OEM method.
Evidence: indications, source availability, transfer position, alarms, load behavior and required delay measurement meet the approved equipment-specific criterion.
StatusPass / Fail / N.A. / Deferred
Perform the approved retransfer and return sequence.
Evidence: restore delay, final position, generator cooldown/run-on and indications are recorded against approved criteria with no unexplained alarm.
StatusPass / Fail / N.A. / Deferred
Verify bypass/isolation status and function only when explicitly permitted.
Evidence: OEM procedure, site plan and competent authority permit the test; record state, key/interlock behavior and as-left position. Otherwise choose Deferred.
StatusPass / Fail / N.A. / Deferred
Verify alarm annunciation, remote indication, building monitoring and event logging for in-scope events.
Accept when: signals reach the intended endpoint and timestamps correlate with the test record.
StatusPass / Fail / N.A. / Deferred
Verify voltage, frequency, phase and source-availability behavior only by the OEM-approved method.
Evidence: criteria trace to the installed controller/system; no generic pickup, dropout or synchronization value is substituted.
StatusPass / Fail / N.A. / Deferred
E
Electrical test control, defects and close-out
Make every reading traceable, every unresolved condition owned and the final operating state explicit.
Points 25–27
Control every electrical condition test in scope.
Record: approved method, isolation boundary, instrument category/rating/calibration, points, specified stimulus/test voltage, criterion and reading. Do not perform unsanctioned dielectric or insulation tests.
StatusPass / Fail / N.A. / Deferred
Document defects, thermal findings, abnormal readings, alarms, wiring discrepancies and damage.
Evidence: location, photographs/data, risk, compensating measure, owner, due date, operational impact and required retest.
StatusPass / Fail / N.A. / Deferred
Complete the as-left verification and operations handoff.
Record: source, controller, bypass/isolation, generator, covers/labels, cleared tools, restored energy-control status, notifications, next due date and independent/owner sign-off. Keep Fail and Deferred visible.
StatusPass / Fail / N.A. / Deferred
Work-order evidence package
Attach six records that make the checklist auditable
A check mark without identity, authority, measurement context or an as-left state cannot support troubleshooting, review or the next maintenance cycle.
Status discipline
Blank is not pass—and Deferred is not failure
Use one explicit status for every checkpoint. The status describes today's evidence, not optimism about the equipment.
Criterion met
The approved requirement is known, the in-scope work is complete and objective evidence supports acceptance.
Criterion not met
An observed condition, result or final state fails the applicable requirement. Record risk, controls, owner and retest.
Not applicable
The feature or task is outside this exact ATS configuration or approved scope. Document the reason—do not leave it blank.
Not completed yet
Authority, document, outage, instrument, access or criterion is unavailable. Preserve the open item and next action.
Close-out rule: Pass items can close. Fail and Deferred items stay visible with ownership. N.A. requires a reason. Blank rows remain incomplete.
Maintenance program questions
Frequently asked questions
How often should an ATS be maintained?
Set the interval from the equipment OEM, the installation's legal/insurance requirements, critical-load risk, operating environment, generator program, duty history, and site maintenance standard. A calendar-only interval is incomplete; abnormal operation, heat evidence, alarms, contamination, or modifications can justify earlier review.
Can I use a standard torque chart for ATS lugs?
No. Use the torque value specified for the exact ATS terminal, conductor/lug arrangement, and hardware. If the rating label, OEM manual, or approved project documentation does not provide it, obtain an authoritative specification before torqueing that point.
What tests belong in ATS preventive maintenance?
The exact scope is site- and model-specific, but commonly includes documented visual/mechanical inspection, controller/settings verification, approved functional transfer and retransfer observation, alarm/remote-monitoring verification, and any OEM/site-approved electrical condition tests. Each test needs a defined method and acceptance criterion.
Should a technician change ATS controller settings during maintenance?
Not as a routine maintenance action. Compare the installed settings against the approved settings record, preserve a backup where available, and use formal authorization plus re-testing for any change. Transfer and source-acceptability settings can affect critical loads and generator operation.
What does “as-left” mean for an ATS?
It records the final operational state: the source supplying the load, controller mode, generator mode, bypass/isolation state, alarm condition, covers/labels, unresolved defects, and the person who accepted the return to service. It is the handoff point between maintenance and operations.
Further project control
Related resources and primary technical sources
Related SENTOP resources
Automatic transfer switch product rangeTransfer switch selection guideHow to safely plan ATS installationATS terminology and system contextOEM and ODM project supportStandards and certificatesPrimary technical sources
- OSHA 29 CFR 1910.333 — selection and use of work practices for electrical safety.
- OSHA 29 CFR 1910.147 — control of hazardous energy.
- OSHA interpretation, 12 December 2012 — electrical de-energization verification and indicator limitations.
- NFPA 70B, 2026 edition — electrical equipment maintenance program framework; apply only where governing and with exact equipment data.
- NFPA 110, 2025 edition — emergency and standby power systems where applicable.
- IEC 60947-6-1:2026 — transfer switching equipment product standard.
- ASCO 7000 Series G/Q/S/U Frame manual 381333-414 — one current family-specific example, not a universal ATS manual.
- ASCO Series 185 functional-test guidance — exact-series procedure example.
- Eaton IB140042EN, April 2025 — current manual example; always confirm applicability to the installed product.
Send the asset record—not a generic torque chart
For ATS project support, share the exact model and nameplate, one-line, controller, source arrangement, transition type, approved settings, work scope, applicable manuals, fault/maintenance history, critical-load constraints and requested evidence package.
