Standing in front of a Square D transformer trying to figure out how old it is, or what the model number means? This guide gives you the complete Square D transformer date code decoder, model number format breakdown, and nameplate reading guide — sourced directly from official Schneider Electric documentation.
⚡ Quick Answer
Do Square D dry-type transformers have serial numbers? No. Per Schneider Electric official FAQ, LV dry-type transformers (<600V) are not serialized. They use a date code instead.
Modern date code (post-Aug 1996): YYWW — first 2 digits = year, last 2 = work week.
Example: 1042 = manufactured in week 42 of 2010.
📋 Table of Contents
1. Why Square D Dry-Type Transformers Have No Serial Number
This surprises many electricians and maintenance technicians: Square D (Schneider Electric) does not put serial numbers on dry-type low voltage distribution transformers under 600V.
This is documented in official Schneider Electric FAQ FA97652:
“No, SquareD/Schneider Electric does not serialize Dry Type Low Voltage Transformers (<600V). However, Medium Voltage Transformers (>600V) are identified by serial numbers on the nameplate, as they are most often built to order per individual specifications.”
— Schneider Electric FAQ FA97652, Published 6/3/2002
What this means in practice:
- If you need to identify a dry-type Square D transformer (<600V), use the date code and catalog/model number on the nameplate.
- If you have a Square D medium voltage transformer (>600V) or a padmount, it will have a serial number — use that to contact Schneider Electric for full records.
- For warranty claims or parts on LV units, Schneider Electric uses the catalog number + date code.
2. Modern Date Code System (Post-August 1996)
From August 1, 1996 onward, Square D / Schneider Electric switched to a simple 4-digit numeric date code. This is the system you will find on the vast majority of Square D transformers in service today.
YY WW
Year (2 digits) Work Week (2 digits)
Decoding Examples
| Date Code | Year | Work Week | Approximate Date |
|---|---|---|---|
| 0101 | 2001 | Week 1 | Early January 2001 |
| 1042 | 2010 | Week 42 | Mid-October 2010 |
| 1535 | 2015 | Week 35 | Late August 2015 |
| 2015 | 2020 | Week 15 | Early April 2020 |
| 2315 | 2023 | Week 15 | Mid-April 2023 |
Week 1 = first full week of January • Week 26 = late June/early July • Week 52 = late December.
Most years have 52 work weeks; some have 53. Use a week number calendar to pinpoint the exact dates.
This is also confirmed in Schneider Electric FAQ FAQ000236185: “The first two digits of the date code indicates the YEAR the transformer was manufactured. The next two digits indicates the work WEEK of that year it was manufactured.”
3. Legacy Date Code System (1956–1995)
For older Square D transformers manufactured before August 1996, the company used an alphanumeric date code system documented in Data Bulletin 0110PD9201. This system is more complex — here is how to decode it.
Year Code (Letter-Based, Rotating 21-Year Cycle)
The year is encoded as a single letter that repeats on a 21-year cycle. The letters I, O, Q, Y, and Z were not used after September 30, 1965.
| Year Letter | Possible Years | Year Letter | Possible Years |
|---|---|---|---|
| A | 1950, 1971, 1992 | N | 1962, 1983, 2004 |
| B | 1951, 1972, 1993 | P | 1963, 1984, 2005 |
| C | 1952, 1973, 1994 | R | 1964, 1985, 2006 |
| D | 1953, 1974, 1995 | S | 1965, 1986, 2007 |
| E | 1954, 1975, 1996* | T | 1966, 1987, 2008 |
| F | 1955, 1976, 1997 | U | 1967, 1988, 2009 |
| G | 1956, 1977, 1998 | V | 1968, 1989, 2010 |
| H | 1957, 1978, 1999 | W | 1969, 1990, 2011 |
| J | 1958, 1979, 2000 | X | 1970, 1991, 2012 |
| K | 1959, 1980, 2001 | L | 1960, 1981, 2002 |
| M | 1961, 1982, 2003 | *System changed Aug 1, 1996 | |
Month Code (Letter-Based)
| Letter | Month | Letter | Month | Letter | Month |
|---|---|---|---|---|---|
| A | January | E | May | H | August |
| B | February | F | June | J | September |
| C | March | G | July | K | October |
| D | April | L | November / December* | ||
*Note: During 1951–Sept 1965, September through December used I, J, K, L respectively. After Oct 1965, only A–H and J–L were used (I, O, Q, Y, Z dropped).
Legacy Date Code Examples
| Date Code | Format | Meaning |
|---|---|---|
| BA | Month + Year | February, 1951 / 1972 / 1993 |
| B20A | Month + Day + Year | February 20, 1950 / 1971 / 1992 |
| B20A2 | Month + Day + Year + Shift | February 20, 1950/1971/1992, Shift 2 |
For transformers with the legacy date code, the most reliable way to narrow the year is to use the equipment appearance plus the years in service together. For example, a code of “CA” could be March 1950, 1971, or 1992 — but a 1950 unit would look dramatically different from a 1992 unit. If the unit may predate 1979, also check for PCB-containing oil — EPA regulations require special handling and disposal for pre-1979 oil-filled transformers.
4. Where to Find the Date Code & Nameplate on Square D Transformers
The date code is stamped on the nameplate, not on the transformer body itself. Nameplate location varies by transformer type:
| Transformer Type | Nameplate Location | What to Look For |
|---|---|---|
| Dry-Type Enclosed (Most Common) | Attached to enclosure frame or front door | Look for “Date Code” or “Mfg. Date” field |
| Open/Ventilated Dry-Type | Attached to core/coil assembly | May require removing cover panels |
| Padmount (Liquid-Filled) | Inside cabinet door, left or right panel | Serial number present on these units |
| Substation / Network Transformer | External tank wall, near control cabinet | Serial number always present on MV units |
🔧 Step-by-Step: Finding Your Date Code
- Open the enclosure door or locate the nameplate on the transformer body.
- Look for a metal or polymer label with text including kVA, voltage, and catalog number.
- Find the field labeled “Date Code,” “Mfg. Date,” or “Date.”
- If it’s 4 digits (e.g., “2315”) — use the modern YYWW system.
- If it contains letters (e.g., “B20A”) — use the legacy system table above.
5. How to Read a Square D Transformer Model Number
Square D dry-type distribution transformer catalog numbers encode the key electrical specifications directly in the part number. Here is how to decode them.
Dry-Type Distribution Transformer Format
EE 75 T 3 H
■ kVA Rating
■ Separator
■ Voltage Code
■ Suffix (taps/encl)
| Model Number | kVA | Primary V | Secondary V | Phase | Notes |
|---|---|---|---|---|---|
| 3S1F | 3 | 240x480V | 120/240V | 1Φ | NEMA 3R |
| 7S1F | 7.5 | 240/480V | 120/240V | 1Φ | NEMA 3R, Epoxy |
| 10S1F | 10 | 240x480V | 120/240V | 1Φ | NEMA 3R, 180°C |
| 75T3H | 75 | 480V | 208Y/120V | 3Φ | Standard |
| 150T3H | 150 | 480V | 208Y/120V | 3Φ | 6 taps |
| EE167S3H | 167 | 240/480V | 120/240V | 1Φ | Energy Efficient, Al winding |
| 75T112H | 75 | 480Y/277V | 240V | 3Φ | Sorgel series |
The voltage configuration digits (e.g., the “1840” in 150T1840H) are not publicly documented for every combination. Per SE FAQ FA101941, the “1840” encodes “480 delta primary to 600 delta secondary with no taps.” For any catalog number you cannot decode, contact Schneider Electric Product Marketing/Support directly.
6. Square D Transformer Nameplate Reading Guide
Understanding all fields on a Square D transformer nameplate lets you quickly verify specifications without referencing a catalog. Here is what each field means:
| Nameplate Field | What It Means | Typical Value |
|---|---|---|
| kVA | Apparent power rating — the transformer’s size | 15, 30, 45, 75, 112.5, 150, 225… |
| HV / Primary | Input voltage (High Voltage side) | 480V, 480Y/277V, 240/480V |
| LV / Secondary | Output voltage (Low Voltage side) | 208Y/120V, 120/240V, 240V |
| Hz | Frequency rating | 60 Hz (all US units) |
| Temp Rise | Max winding temp rise above 40°C ambient at full load | 115°C or 150°C (dry type) |
| Insulation Class | Max rated temperature of winding insulation | 180°C (Class H), 220°C (Class R) |
| %Z (Impedance) | Impedance as % of rated voltage; affects fault current | 2–5% for distribution transformers |
| Wt (Weight) | Unit weight for installation planning | Listed in lbs |
| Cat No. | Catalog / model number (use for ordering) | 75T3H, EE167S3H, etc. |
| Date Code | Manufacturing date (YYWW or legacy alpha) | 1042, B20A, etc. |
7. Common Square D Transformer Models & Specifications
| Cat. No. | kVA | Phase | Primary V | Secondary V | Enclosure | Temp Rise |
|---|---|---|---|---|---|---|
| 3S1F | 3 | 1Φ | 240×480 | 120/240 | NEMA 3R | 115°C |
| 7S1F | 7.5 | 1Φ | 240/480 | 120/240 | NEMA 3R | 115°C |
| 10S1F | 10 | 1Φ | 240×480 | 120/240 | NEMA 3R | 115°C |
| 75T3H | 75 | 3Φ | 480 | 208Y/120 | NEMA 2 | 115°C |
| 75T112H | 75 | 3Φ | 480Y/277 | 240 | Type 2 | 150°C |
| EE167S3H | 167 | 1Φ | 240/480 | 120/240 | NEMA 2 | 115°C |
8. Frequently Asked Questions
Does Square D put serial numbers on dry type transformers?
No. Per official Schneider Electric FAQ FA97652, Square D does NOT serialize dry type low voltage transformers under 600V. They use a date code instead. Medium voltage transformers (>600V) do carry serial numbers.
How do I decode a Square D transformer date code?
For modern units (post-August 1996): YYWW format — first 2 digits = year, last 2 = work week. Example: 1042 = week 42 of 2010 = mid-October 2010. For pre-1996 units, use the legacy alpha-numeric system documented in Data Bulletin 0110PD9201.
What does the model number on my Square D transformer mean?
The number before “T” is the kVA rating. The digits after “T” encode the voltage configuration. Prefix “EE” indicates an Energy Efficient (DOE compliant) model. Suffix letters indicate enclosure type and tap configuration. For unknown voltage codes, contact Schneider Electric support.
Where is the nameplate on a Square D transformer?
On dry-type enclosed units, the nameplate is on the enclosure frame or front door. On padmount units, inside the cabinet door. On substation transformers, on the exterior tank wall. See Section 4 for the full location guide.
What year was my Square D transformer made?
Find the date code on the nameplate. If it is 4 digits (e.g., “2315”), first 2 = year (2023), last 2 = work week (15) = mid-April 2023. If it contains letters, use the legacy table in Section 3 above.
How do I find Square D transformer specifications by model number?
Visit the Schneider Electric official Square D transformer page and search by catalog number. For older units no longer in the catalog, the nameplate data is usually sufficient for replacement sizing.
Need a Square D Replacement Transformer?
Once you know the kVA, voltage, and phase from the nameplate, we can help you find a compatible unit — including Schneider Electric replacements and custom alternatives.
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