A winding manufacturer that exports will sooner or later meet this situation: the customer specification says "NEMA MW 1000", whereas the supplier's catalogue is prepared in the language of IEC 60317. The two standards describe the same product but use different grammars.
The Structure of the Standards
IEC 60317 consists of many parts under the heading "specifications for particular types of winding wires". Each part defines a specific product type; for example, general requirements and enamelled round copper wire are covered in 60317-0-1, enamelled flat copper wire in 60317-0-2, and enamelled round aluminium wire in 60317-0-3. The part number is itself the address that describes the product.
NEMA MW 1000, on the other hand, holds separately numbered specifications for each film type and conductor form within a single document. If you see a specification number starting with "MW" in an order, that number points directly to the product type.
Key Differences
| Topic | IEC 60317 | NEMA MW 1000 |
|---|---|---|
| Publisher | IEC (international) | NEMA (North America) |
| Document structure | Multi-part series (60317-0-1, 0-2, 0-3 …) | Single document, with MW specifications inside |
| Measurement system | Metric (mm) | AWG-based, with metric equivalents |
| Build class | Grade 1 / Grade 2 / Grade 3 | Single build / Heavy build / Triple build |
| Thermal notation | IEC 60085 class (155, 180, 200, 220) | Temperature degree (°C) within the specification |
| Test methods | In a separate standard: IEC 60851 series | Within the same document, referencing ASTM methods |
Measurement System: The Most Common Trap
AWG steps and metric diameter steps do not overlap exactly. The millimetre equivalent of an AWG number usually corresponds to a value with decimals; rounding to the nearest metric step creates a percentage deviation in the section area. Though it looks like a small deviation, it has a measurable effect on resistance and copper loss in a winding of thousands of turns. When switching between standards it is therefore safer to match over the section area, not the diameter.
Build Class and Tolerances
Grade 1/2/3 and single/heavy/triple build overlap conceptually: both express increasing film thickness. But the allowed minimum and maximum dimension increases and the minimum breakdown-voltage values are not exactly the same in the two standards. The shortcut assumption "heavy build equals Grade 2" must therefore be verified against the dimension tables in critical applications.
Test Approach
On the IEC side the test methods are separated from the product standard: elongation, springback, flexibility-adhesion and abrasion fall under IEC 60851-3; dielectric breakdown and insulation continuity under IEC 60851-5; thermal shock and cut-through under IEC 60851-6. On the NEMA side the test methods are defined within the same document framework, referencing ASTM standards. The measured quantities are largely the same; the difference is in the detail of sample preparation and acceptance criteria.
The Certification Side
The most concrete place the standard difference shows is in the documents. In the IEC world the product is defined by a declaration of conformity to the relevant 60317 part; the shipped batch by an EN 10204 3.1 inspection certificate. These two are different things: the first shows the conformity of the product type to the standard, the second the values actually measured on that batch. Specifications often ask for both.
Customers working on the NEMA side usually request a declaration of conformity referencing the relevant MW specification number and a test report. It is possible to provide both references for the same product; but this must be stated at the order stage, because the documents rest on the inspection records made during production.
Another practical detail: because the dimension tables of the two standards differ, when issuing a document with two different references for the same batch, the dimension values must fall within the tolerance range of both tables. This is a point to check in advance, especially at boundary dimensions.
Practical Recommendations
- Do not write only "IEC compliant" in the order text; state the part number and the build class.
- In AWG–metric transitions, take the section area as the reference, not the diameter.
- Write the thermal class with both the class number and the temperature value; it removes the chance of misunderstanding.
- If conformity to both standards is wanted, state it at the order stage; issuing a document afterwards is often not possible.
Summary
Both standards serve the same purpose: to define the winding wire's dimension, insulation thickness, electrical strength and thermal behaviour. The difference lies in how this definition is organised and in which measurement system it is expressed. IEC 60317, as a multi-part series, handles product types separately and leaves the test methods to the IEC 60851 series; NEMA MW 1000 holds both product and test definitions under a single document framework.
What matters in practice is to leave no ambiguity in the order and specification text: when the product standard and part number, build class, thermal class and requested document types are written clearly, the transition between the two standards is managed smoothly.