TIW vs. FIW vs. Enamelled Wire with Tape: Choosing the Right Winding Insulation for Your Transformer

When you design an isolating transformer, there are three mainstream ways to achieve reinforced insulation between the primary and secondary sides: conventional enamelled wire plus insulating tape, triple insulated wire (TIW), and fully insulated wire (FIW).All three can pass safety certification;the differences lie in size, process steps, cost structure and design freedom.This article compares them from a neutral, specification-driven perspective to help you choose according to your product's conditions.

How the Three Approaches Work

Conventional enamelled wire + insulating tape: The winding itself carries only an enamel film (basic insulation). Isolation between primary and secondary is achieved through interlayer insulating tape plus creepage distance margins reserved on both sides of the bobbin. The process is mature and the wire itself is the cheapest of the three — but the tape and edge margins consume winding-window space, making it hard to shrink the transformer, and the workflow involves more steps: winding, taping, and lead dressing.

Triple insulated wire (TIW): three insulation layers are extruded over the conductor; taking DAH JIN's TLW-B / TLW-BB / TLW-B7S / TLW-F as an example, three extruded insulation layers, evaluated under VDE 40008834 per IEC 62368-1 Annex J as reinforced insulation (Reinforced / Extruded / 3 layers). Because the insulation is built into the wire itself, primary and secondary can be wound directly together, eliminating the need for interlayer tape and creepage distance, so the transformer can be made noticeably smaller with fewer process steps.

Fully insulated wire (FIW): a winding wire whose thickened enamel film is built up in multiple continuous coats by the enamelling process (specified per IEC 60317-56:2017, thermal class 180);since the 3rd edition of IEC 62368-1 it can be used for reinforced insulation under defined conditions.Conductor size ranges side by side: FIW (IEC 60317-56) conductor 0.090–0.900 mm; DAH JIN's certified coverage depends on the certification body — UL E236542 covers 0.11–1.5 mm for TLW-BB, while VDE 40008834 covers 0.10–1.00 mm for TLW-B / TLW-BB / TLW-F.FIW suits extremely compact high-frequency designs, but the film is a continuous layer of a single material, so its safety-qualification path and wire termination differ from TIW, and some applications still require additional insulation measures to confirm withstand voltage and creepage.

Quick Comparison

Enamelled wire + insulating tape

• How reinforced insulation is achieved: tape + creepage distance
• Winding process steps: the most (taping, edge margins)
• Wire termination: enamel stripping required
• Safety path: construction-based evaluation

Triple insulated wire (TIW)

• How reinforced insulation is achieved: three extruded insulation layers on the wire
• Winding process steps: few (primary and secondary wound directly together)
• Wire termination: DAH JIN's TLW-B / TLW-BB / TLW-B7S / TLW-F can be soldered directly without first stripping the insulation (per product data)
• Safety path: the wire path of IEC 62368-1 Annex J / 61558-1 Annex K

Fully insulated wire (FIW)

• How reinforced insulation is achieved: thickened enamel film (single material)
• Winding process steps: few
• Wire termination: solderable type (IEC 60317-56 solderable), with soldering conditions per the manufacturer's specification
• Safety path: the FIW path from IEC 62368-1 ed. 3 onward

When to Choose TIW

1. Chargers and compact SMPS transformers (IEC 62368-1 Annex J): In the power-density race for phone and laptop chargers, the volume saved by eliminating tape and edge margins translates directly into a smaller end product.
2. Solder-friendly production lines: The DAH JIN TLW series is directly solderable without stripping first, requiring fewer termination steps than either enamelled wire or FIW.
3. Medical power supplies (EN/IEC 60601-1): TLW-BB and TLW-B7S can help meet patient-isolation requirements (actual withstand voltage depends on the medical-grade verification of the end equipment).
4. High-frequency designs where skin effect matters: The stranded TLW-B7S (seven strands, concentric round-stranded) reduces AC resistance while retaining full triple insulation.