The thickness of electrical steel laminations is the single most adjustable lever for controlling eddy-current losses — and its effect is dramatic. Cutting lamination thickness in half reduces eddy-current losses to one-quarter. But thinner material is harder to punch, more expensive to produce, and increases stacking time. This guide covers the full thickness range from 0.05 mm ultra-thin to 0.65 mm standard, helping you match gauge to application without overspending or underperforming.
Core Key Points
- Eddy-current losses scale with the square of thickness: halving gauge reduces eddy losses by 75%.
- At 50 Hz, 0.27–0.35 mm is the optimal range for most transformer and motor applications — thinner offers diminishing returns.
- Above 400 Hz (EV motors, high-frequency transformers), ultra-thin grades of 0.10–0.20 mm become essential for loss control.
- CRGO is available in 0.10–0.35 mm; CRNGO covers 0.05–0.65 mm (standard) with ultra-thin down to 0.05 mm for high-speed EV drivetrains.
- Stacking factor decreases with thinner gauges: 0.35 mm achieves ~0.97, while 0.10 mm may achieve only 0.88–0.92, which must be accounted for in core design.
The Physics: Why Thickness Matters
When a changing magnetic flux passes through a conductive lamination, it induces circulating currents — eddy currents — that dissipate energy as heat. The power lost to eddy currents is proportional to:
P_eddy ∝ d² × f² × B²
Where d = lamination thickness, f = frequency, B = flux density. Because thickness appears squared in this relationship, gauge selection has a disproportionately large effect on eddy-current losses at high frequencies.
Practical example: At 400 Hz (EV motor operating frequency), moving from 0.35 mm to 0.20 mm reduces eddy-current losses by approximately 67% — a transformation that cannot be achieved by any other single material or design change.
Hysteresis losses, by contrast, are largely independent of thickness and depend on material grade and operating flux density. This means at low frequencies (50/60 Hz), hysteresis dominates and the benefit of going thinner is smaller than intuition suggests.
Standard Thickness Ranges and Their Applications
0.65 mm — Economy Motors and Low-Frequency Transformers
The thickest standard electrical steel gauge, 0.65 mm CRNGO is the most economical option. Eddy-current losses are high relative to thinner gauges, but for 50 Hz economy motors (IE1 class) and small auxiliary transformers where first cost is paramount, 0.65 mm remains widely used.
Stacking factor: ~0.97–0.98
Core loss range (1.5 T, 50 Hz): 4.0–6.0 W/kg
Applications: Small induction motors, auxiliary transformers, ballasts
0.50 mm — Standard Industrial Motors
The workhorse of industrial motor manufacturing. At 50 Hz, 0.50 mm CRNGO achieves a reasonable balance between eddy-current performance and punching efficiency. Used extensively in IE2 and IE3 induction motors for industrial pumps, fans, and compressors.
Stacking factor: ~0.97
Core loss range (1.5 T, 50 Hz): 2.5–4.5 W/kg
Applications: General-purpose induction motors (IE2/IE3), generators up to ~1 MVA
0.35 mm — High-Efficiency Motors and Standard Transformers
The transition gauge between “standard” and “high-performance.” At 0.35 mm, both transformers and motors see meaningful efficiency gains over 0.50 mm. This is the standard gauge for IE3 and IE4 motors and for distribution transformer CRGO (economy class).
CRGO 0.35 mm core loss (1.7 T, 50 Hz): 1.30–1.55 W/kg
CRNGO 0.35 mm core loss (1.5 T, 50 Hz): 2.5–3.5 W/kg
Applications: Distribution transformers (economy class), IE3/IE4 induction motors
0.30 mm — Premium Transformers and Efficient Motors
The most widely specified CRGO thickness for distribution transformers meeting IEC A and A0 efficiency classes. Also used for premium CRNGO in high-efficiency motor applications.
CRGO 0.30 mm core loss (1.7 T, 50 Hz): 1.10–1.20 W/kg
Applications: 50 Hz distribution transformers (A and A0 class), large induction motors (IE4+)
0.27 mm — High-Efficiency Transformer CRGO
Specified for IEC A0 and AA0 class transformers and for designs where size constraints demand the highest flux density. The 0.27 mm gauge (B27Gxxx) reduces eddy-current losses by approximately 10% compared to 0.30 mm — worth the additional cost for premium transformer designs.
CRGO 0.27 mm core loss (1.7 T, 50 Hz): 1.00–1.20 W/kg
Applications: AA0/A0 class transformers, large power transformers
0.23 mm — Maximum Efficiency at 50/60 Hz
The thinnest conventionally practical CRGO for 50/60 Hz power transformers. At 60 Hz (North America, Japan), eddy-current losses are 44% higher than at 50 Hz, making 0.23 mm frequently necessary to meet efficiency standards. In the EU at 50 Hz, 0.23 mm is reserved for the most demanding AA0 class or very large power transformers (≥ 100 MVA).
CRGO 0.23 mm core loss (1.7 T, 50 Hz): 0.85–0.95 W/kg
Applications: 60 Hz high-efficiency transformers, large power transformers (≥ 100 MVA)
Ultra-Thin Silicon Steel (≤ 0.20 mm)
Ultra-thin electrical steel — below 0.20 mm — is a specialized category with unique manufacturing requirements and a rapidly growing market driven by EV adoption and high-frequency power electronics.
0.15–0.20 mm
Used in medium-frequency applications (200–1,000 Hz) and premium EV motor designs. Both CRGO (for high-frequency transformers) and CRNGO (for EV stator laminations) are available at these gauges.
Core loss range (0.20 mm CRNGO, 1.0 T, 400 Hz): ~12–18 W/kg
Core loss range (0.20 mm CRGO, 1.7 T, 400 Hz): ~6–10 W/kg
Applications: EV traction motors (400 Hz range), medium-frequency inductors, traction transformers
0.10 mm and Below
At 0.10 mm and thinner (available down to 0.05 mm from Zhongxin Steel in CRNGO), eddy-current losses are dramatically reduced for high-frequency EV motor applications. These ultra-thin gauges require specialized slitting equipment with tight thickness tolerances (±0.005 mm at Zhongxin Steel).
Key challenge: Stacking factor decreases to 0.88–0.92, and punching dies wear faster. Laser cutting is often required for prototyping.
Applications: High-speed EV motors (800–2,000 Hz), aerospace motors, medical device actuators
Thickness Selection Matrix
| Application | Frequency | Recommended CRGO | Recommended CRNGO |
|---|---|---|---|
| Distribution transformer (AA0/A0 EU) | 50 Hz | 0.27 mm | N/A |
| Distribution transformer (A class EU) | 50 Hz | 0.30 mm | N/A |
| Power transformer (DOE TP-2, 60 Hz) | 60 Hz | 0.23 mm | N/A |
| General induction motor (IE2) | 50 Hz | N/A | 0.50 mm |
| High-efficiency motor (IE3/IE4) | 50 Hz | N/A | 0.35 mm |
| EV traction motor (permanent magnet) | 400 Hz | N/A | 0.20 mm |
| High-speed EV motor | 800–2,000 Hz | N/A | 0.10–0.15 mm |
| High-frequency power supply transformer | 200–1,000 Hz | 0.15–0.20 mm | N/A |
| Reactor / inductor (50 Hz) | 50 Hz | 0.30–0.35 mm | 0.35–0.50 mm |
Cost and Processing Considerations by Thickness
Thinner electrical steel is more expensive per kilogram for three reasons:
- More rolling passes — Each cold-rolling pass reduces thickness by 20–40%; reaching 0.10 mm requires 5+ passes vs. 2–3 for 0.35 mm.
- Higher rejection rate — Dimensional tolerances are tighter; scrap rates increase.
- Slower production speed — Thinner gauges require slower mill speeds to maintain surface quality.
Approximate price premium over 0.35 mm base grade (indicative, 2026):
| Thickness | Premium vs. 0.35 mm |
|---|---|
| 0.30 mm | +5–8% |
| 0.27 mm | +10–15% |
| 0.23 mm | +18–25% |
| 0.20 mm | +35–50% |
| 0.15 mm | +60–90% |
| 0.10 mm | +120–180% |
The break-even analysis must consider: material premium vs. operating loss reduction over service life × energy cost × transformer or motor capacity.
FAQ
Why doesn’t everyone use 0.10 mm electrical steel for maximum efficiency?
At 50 Hz, the eddy-current reduction from 0.35 mm to 0.10 mm is significant but the hysteresis loss — which is frequency-independent — remains constant. At 50 Hz, 60–70% of total core loss in a typical transformer is hysteresis-related, meaning ultra-thin laminations provide diminishing returns. Additionally, stacking difficulty, die wear, and material cost all increase sharply below 0.20 mm. Ultra-thin gauges are justified starting at ~200 Hz and above.
What is the stacking factor for 0.27 mm CRGO?
Typical stacking factor for 0.27 mm CRGO is 0.96–0.97, meaning approximately 3–4% of the core volume is occupied by insulation coatings rather than steel. At 0.10 mm, the stacking factor drops to 0.88–0.92 due to the proportionally thicker coating layer.
Can I use 0.35 mm CRGO instead of 0.30 mm to reduce core weight?
Thicker CRGO does not reduce core weight — it is used for the same core design. However, it does reduce cost and is acceptable when the efficiency class requirement allows it. For IEC B class transformers, 0.35 mm is often the right choice. For A class and above, 0.30 mm or better is recommended.
What is the thinnest CRGO commercially available?
Commercially available CRGO is produced as thin as 0.10 mm (e.g., Zhongxin Steel ultra-thin CRGO). Research-grade CRGO down to 0.05 mm exists but is not commercially produced in volume. CRNGO is available in 0.05 mm gauge from specialized producers including Zhongxin Steel for EV motor applications.
References
- Cullity, B. D. & Graham, C. D. (2009). Introduction to Magnetic Materials (2nd ed.). Wiley-IEEE Press.
- IEC 60404-8-7:2023 — Cold-rolled grain-oriented electrical steel strip and sheet. Geneva: IEC.
- IEC 60404-8-4:2022 — Cold-rolled non-oriented electrical steel strip and sheet. Geneva: IEC.
- Pluta, W. A. (2018). “Core Loss Models in Electrical Steel Sheets and Their Validation.” IEEE Transactions on Magnetics, 54(7), 1–5.
- International Energy Agency (2024). Global EV Outlook 2024 — Motor Materials and Efficiency. Paris: IEA.