Free checklist
Dry-type transformer annual maintenance checklist
The annual dry-type transformer service is the deep pass: the measurements, cleanings and tests a quarterly round doesn't reach. This checklist keeps the full service on record with the photos that make it defensible later. Work is commonly verified against NFPA 70B, NETA maintenance testing standards. Confirm the edition your authority having jurisdiction has adopted.
The checklist
Every item, and the photo evidence it needs
The photo count on each row is what RTI would require before the item can be submitted. Work the list here and watch the gate hold, or load it into RTI and let it enforce the real thing.
Outage planning
Shutdown and downstream loads agreed with the owner
Outage window, the panels and loads this unit feeds, any temporary power and the re-energizing order agreed with the owner, and affected occupants told beforehand.
No photoBackfeed and auxiliary supplies listed on the switching plan
Any secondary tie, generator or solar backfeed and any fan or controller supply named on the plan so each gets its own lock, not only the primary disconnect.
No photo
Isolation and cleaning
Transformer locked out and verified dead
Primary and secondary isolation confirmed, absence of voltage tested, lockout applied before any cover comes off.
Windings and enclosure cleaned of dust and debris
Coils and cooling ducts vacuumed and wiped, dust and any tracking film removed from the coil faces and insulators rather than blown around.
Connections and coils
Bolted connections checked to torque
Primary, secondary and tap connections torque-verified or resistance-measured per the manufacturer, re-torqued only where found loose, any that moved noted for re-scan.
Coils, insulators and taps inspected
No cracked or chipped insulators, no discoloration or heat-glazing on the coils, tap links seated and matched to the intended setting.
Core clamps and coil blocking checked for tightness
Core clamping bolts and coil blocks checked against the manufacturer's value, no shifted spacers, and no rust bloom on the core laminations.
Vibration isolation pads and shipping brackets inspected
Pads under the core and coil assembly intact and not crushed, and no shipping bolt or bracket left in place that carries vibration into the enclosure.
Core ground strap and any system bonding jumper inspected
Core ground strap intact and tight, and the neutral bonding jumper, where the system is bonded here, landed with torque verified and no heat marks.
Testing observed and recorded
NETA electrical tests witnessed and logged
Insulation-resistance and any turns-ratio results from the testing tech recorded against the unit, out-of-range values flagged before re-energizing.
Test report with prior-year trend sent to the owner
Firm's written results set against prior outages and the factory test sheet, delivered to the owner, open deficiencies listed for the owner or engineer's acceptance.
No photo
Return to service
Coils cleared and every panel refastened before energizing
No tools, rags, test leads or temporary grounds left on the coils, all panels and vent screens back, and each lock removed by the person who hung it.
Unit re-energized and secondary voltage read per phase
Primary closed in the agreed order, secondary voltage on each phase read under the energized-work procedure within the nameplate range at the set tap, loads returned and the owner told.
Fan and alarm controls tested after energizing where fitted
Where fans or a temperature controller are fitted, its test function run with the panels on, fans starting and the alarm reaching the building system.
No photoRemade connections rescanned once load returns
After the unit has carried load for a while, connections scanned through the vents or any viewing window and the hum compared with the pre-outage baseline.
What usually sends this back
The failures are almost always the evidence, not the work
- Coils blown out with compressed air that just packs conductive dust deeper into the winding slots instead of vacuuming it out.
- Bolted connections re-tightened by feel with no torque wrench, so half are over-crushed and half never reached spec.
- The unit closed up and returned to service before the testing tech's insulation-resistance readings are back and recorded.
Verified against
Common questions
6 answers
- What does this dry-type transformer annual checklist cover?
- 15 items across 5 sections, covering outage planning, isolation and cleaning, connections and coils, testing observed and recorded, and more. Each item spells out what the person walking the job is actually looking for, not just a box to tick.
- Who should run this inspection?
- The facility electrician recording the inspection during a planned outage, working the connections while the testing firm performs the electrical tests on the same unit.
- When in the schedule should this walk happen?
- Once a year during a scheduled shutdown, coordinated with the NETA technician so the transformer is locked out, cleaned and torqued while it's cold, then tested before it's re-energized.
- Why do these items ask for a photo?
- 11 of the 15 items call for photo evidence, 15 photos in all. A checklist answer without the photo is a claim; the photo is what makes the record worth something in a dispute and lets a reviewer approve work without re-walking the job.
- What most often fails a dry-type transformer annual inspection?
- Coils blown out with compressed air that just packs conductive dust deeper into the winding slots instead of vacuuming it out. Bolted connections re-tightened by feel with no torque wrench, so half are over-crushed and half never reached spec. The unit closed up and returned to service before the testing tech's insulation-resistance readings are back and recorded.
- Can I use this checklist in RTI?
- Yes. Start a free RTI workspace, build this list as a checklist, and the Photo Gate holds the submit button until every mandatory item is answered and its photos are attached. Approved inspections roll into a branded turnover package with a tamper evident audit trail.
Run it with the Photo Gate
A checklist nobody can submit half-finished
Load this list into RTI, stick a QR tag on the area it covers, and the submit button stays locked until every mandatory item is answered and the 15 required photos exist. Approved walks roll into a branded turnover package with a tamper evident record behind every line.
See all 508 checklists · 6741 items and 5984 photo requirements in total.