How to Read a Transformer Nameplate
Step-by-step guide to reading kVA, primary/secondary voltage, impedance, winding material, and serial data from a transformer nameplate before you sell.
The nameplate is the transformer's birth certificate — one clear photo of it tells us nearly everything needed for a firm offer. This guide decodes each field so you know exactly what you own and what drives its value.
Find the nameplate on the tank front or side (padmounts: inside the front hood, on the divider panel). It's a metal plate, usually aluminum, stamped or engraved. Photograph it straight-on with the whole plate in frame.
Nameplate Fields Decoded
| kVA | Capacity rating — the single biggest value driver |
|---|---|
| HV / Primary volts | e.g., 12470GrdY/7200 — the incoming utility voltage |
| LV / Secondary volts | e.g., 480Y/277 — what the building uses; common = valuable |
| %Z (Impedance) | Matters for paralleling; 5.75% is the common standard |
| Winding material | CU (copper) or AL (aluminum) — CU adds 15-30% |
| Serial & year | Age and factory traceability; post-1979 = presumed non-PCB |
| Oil type & gallons | Mineral or FR3; volume matters for transport planning |
| Weight | Total and untanking weights — sets rigging and freight |
The three photos that get you a same-day offer
One: the full nameplate, straight-on and legible. Two: the whole unit from the front showing bushings or terminals. Three: the surroundings showing loading access. With those three frames we can usually quote common configurations within one business day.
What if the nameplate is missing or unreadable?
We can still work with it: measurements, bushing count and style, tank dimensions, and any stenciled utility numbers narrow the identification. Expect conservative pricing until physical inspection — missing nameplates force worst-case assumptions on winding material and PCB status.
Ready to sell? Get your offer today.
Send photos and nameplate details — we respond with a firm offer, typically within 24 hours. Freight and rigging arranged nationwide, payment before pickup.
Frequently Asked Questions
- Where is the nameplate on a padmount transformer?
- Open the front hood (it may be pentabolt-secured): the plate is on the divider panel between the HV and LV compartments.
- What does 'No PCB' on the nameplate mean?
- The unit shipped with non-PCB oil — a meaningful value protector for pre-1990s units. Photograph that label too.
- The plate lists two kVA ratings — which counts?
- Both: the base (OA/ONAN) rating and the fan-cooled rating. Quote conversations use the base rating by convention.
Authoritative References
- NEMA — Transformer product standards — the manufacturer association whose standards govern nameplate marking conventions on North American transformers.
- EPA — PCB marking and labeling requirements — background on the 'No PCB' labeling and why post-1979 units are presumed non-PCB.
- IEEE C57.12.00 — General requirements for transformers — the standard that defines the rating data (kVA, voltage, impedance) stamped on every nameplate.