Aramid Paper (Nomex®) Insulated Wires
Aramid paper insulated wires for dry-type transformers and high-temperature machines; classes 200–220.
Unlike cellulose, aramid paper is produced from synthetic aromatic polyamide fibre and can largely retain its dielectric properties when it takes up moisture. Because it can operate continuously up to class 220, withstand short-term overloads without charring and not support flame propagation, it has become the standard insulation for dry-type transformers.
Nomex and Metastar type aramid papers are assessed to the requirements for non-cellulosic electrical paper under IEC 60819. They are wound onto the conductor with overlap; on request, impregnating resin is applied over the paper to obtain a compact insulation block that becomes a single piece within the winding.
Aramid Paper (Nomex®) Insulated Wires Products
Technical Information
- Thermal class: 180 (H) – 220 (R), 240 (C) depending on structure
- Paper thickness: 0.05 – 0.25 mm (per layer)
- Overlap: 50% (half-overlap) standard
- Preservation of dielectric properties in humid environments
- Reference: IEC 60819 (non-cellulosic papers), IEC 60085 (thermal class)
In dry-type transformers the insulation class directly determines the overload capacity. A winding with Class 220 aramid insulation allows a higher temperature rise than a Class 155 winding of the same section; this means higher rated power or a wider overload window in the same physical size.
Aramid insulation is the technical justification for choosing dry-type over oil-type in enclosed spaces where the fire load and smoke toxicity must be limited — hospitals, metros, shopping malls, high-rise buildings.