Nameplate · Serial number · Date code
Transformer Serial Number & Date Code Decoder
Enter the code from the nameplate. The tool reads the manufacture date for brands that publish their format and says so plainly for the ones that do not.
By Allen Tan · Updated · How results are sourced
1Nameplate
Rule published by the manufacturer.
Spaces and dashes are ignored. The value shown is the manufacturer’s own example. Replace it with the code from your nameplate.
Manufactured
August 9, 2017
Eaton / Cooper Power — dry-type
How it was read
- Format
- Current: J-YY-M-DD-nnnnn
- Year
- 2017 (from “17”)
- Month
- August (letter H)
- Day
- 9
- Sequence
- 12358
Share this result
https://kvcalc.com/tools/transformer-serial-number-decoder/
The link carries the full calculation, so anyone opening it lands on the same inputs and the same result.
Formats this tool can read
The first three rows were published by the manufacturer. The last two are reported rules from a state-hosted PCB guideline. They are marked as such in the result.
| Brand and product | Format | Example | Source |
|---|---|---|---|
| Eaton / Cooper Power, dry-type | J-YY-M-DD-nnnnn | J17H0912358 = Aug 9, 2017 | Eaton Knowledge Hub |
| Eaton / Cooper Power, dry-type (older) | J-YY-M-nnnnn | J17H12345 = Aug 2017 | Eaton Knowledge Hub |
| Schneider Electric / Square D, low-voltage | YYWW | 1042 = week 42, 2010 | Schneider Electric Canada FAQ |
| GE distribution, 1965–1981 (reported) | L-nnnnnn-PMYW | L714041TJMA = Sep 1976 | PCB-status guideline |
| Westinghouse distribution, pre-1980 (reported) | YY… first two digits | 69A03964 = 1969 | PCB-status guideline |
Eaton’s month letters run A to M and skip I: A to H are January to August, J to M are September to December.
Serial number lookup by brand
Westinghouse transformer serial number lookup
For older Westinghouse distribution transformers the first two digits are the year, so69A03964 is a 1969 unit made in Athens, GA. We found no Westinghouse document that states this rule, so treat the result as a reported date. Newer or non-distribution units may not follow it.
GE transformer serial number lookup
GE distribution units from 1965 to 1981 end in four letters: plant, month, year, winding.L714041TJMA reads as Shreveport, September 1976, aluminum. GE used no date code before 1965, and a unit built after 1981 will not decode here.
Square D transformer date code
Schneider Electric’s FAQ for low-voltage transformers reads the date code as year then work week. 1042 is week 42 of 2010. The FAQ is published for Canada, so confirm with Schneider for US units.
Eaton transformer serial number lookup
Eaton dry-type serials start with J, then the year, a month letter (A to M, skipping I) and the day. J17H0912358 is August 9, 2017. This does not apply to Eaton or Cooper liquid-filled units.
The same PCB-status guideline lists rules for a few other older makers: Central-Moloney (second and third digits are the year), A. B. Chance (first two digits are the year, then a month letter), Kuhlman (last two digits are the year since 1979) and McGraw-Edison (first two digits are the year since 1969). The tool does not decode these yet.
Brands with no published rule
We looked for a manufacturer document for each of these and did not find one. That is a finding about what we checked, not proof that no rule exists. Some pages were unreachable (access blocked or script-rendered) and are not counted as checked.
| Brand | What we found |
|---|---|
| Siemens | The Siemens transformer installation, operation and maintenance manual we checked (A6X30122222_J) contains no serial number or date code explanation. Siemens transformer installation, operation and maintenance manual |
| ABB / Hitachi Energy | We found no published serial or date code rule for ABB or Hitachi Energy distribution transformers. |
| Hammond Power Solutions | The Hammond user manual and general product information we checked contain no decoding rule. They mention the date of manufacture only in the warranty terms. |
| Howard Industries | We found no published serial or date code rule for Howard Industries transformers. |
| Acme Electric | We found no published serial or date code rule for Acme Electric transformers. |
| Jefferson Electric | We found no manufacturer-published serial or date code rule for Jefferson Electric transformers. |
| Hevi-Duty / SolaHD | The SolaHD transformer specification guide mentions the date of manufacture only in the warranty terms and gives no decoding rule. SolaHD transformer specification guide |
If you hold a manufacturer document that explains one of these formats, send it through thecorrections contact and we will add the brand with your source.
Disclaimer. A decoded date comes from the serial number format only. It is not a warranty record, a compliance record or engineering advice. A result marked as a reported rule comes from a third-party document and has not been confirmed by the manufacturer. Do not rely on a decoded date alone to decide how to handle, label, test or dispose of a transformer. Check with the owner, the manufacturer or the regulator that applies. Sources listed above were opened and checked on 2026-10-08.
Questions people actually ask
How do I find the manufacture date of a transformer from its serial number?
It depends on whether the maker publishes how the serial number is built. Eaton does for dry-type transformers (J-YY-M-DD-nnnnn) and Schneider Electric does for its low-voltage date code (YYWW). For older GE and Westinghouse distribution units the tool uses rules from a PCB-status guideline and labels the result as reported. For other brands we found nothing, so the tool says so instead of guessing.
How do I read an Eaton dry-type transformer serial number?
The first character is always J. Characters 2 and 3 are the last two digits of the year. Character 4 is the month letter, A for January through M for December, skipping I. Characters 5 and 6 are the day, and characters 7 to 11 are a sequence number. Eaton’s own example: J17H0912358 was made on August 9, 2017. Older serials follow J-YY-M-nnnnn and carry no day.
Does the Eaton rule work for pad-mount or liquid-filled transformers?
No. The Eaton article we cite covers dry-type transformers only. We found no published serial number rule for Eaton or Cooper Power liquid-filled units, so the tool does not apply this one to them.
How do I read the date code on a Square D or Schneider Electric transformer?
Schneider Electric’s FAQ for low-voltage transformers says the first two digits are the year and the next two are the work week. Its example: 1042 means the 42nd working week of 2010. That FAQ is published for Schneider Electric Canada. We found no equivalent US page, so confirm with Schneider for units sold in the US.
Can I decode a GE or Westinghouse transformer serial number?
For older distribution transformers, yes, with a caveat. A PCB-status guideline hosted by the Delaware River Basin Commission lists GE serials from 1965 to 1981 and Westinghouse serials from before 1980, with worked examples. Neither GE nor Westinghouse published these rules for the public, so the tool marks the result as reported. For a newer unit, ask the manufacturer’s service department and give them the serial number and catalog number.
Why does the tool read two digits as 20YY?
Eaton’s article describes the year characters as the last two digits of the year and gives 17 for 2017. A two-digit code cannot tell 2017 from 1917, so the tool reads it as 20YY and rejects any result that falls in the future. A unit that is older than 2000 will not decode correctly.
Does the tool store the serial number I enter?
No. The decoding runs in your browser. The brand and serial number are written into the page address so you can bookmark or send the result. Nothing is sent to a server by the tool.