Does Your Product Need Triple Insulated Wire? One Table Shows Which Transformer Stage Should Use TIW

This article is written for power-supply, magnetics, safety-compliance and purchasing engineers: in the end product on your desk, should a given power stage or transformer inside it use triple insulated wire (TIW)? Rather than asking unit by unit, first understand one principle and three criteria, then locate your own case on a selection map in thirty seconds. The whole article gives direction and criteria only; the wire diameters, withstand voltages and all other values of DAH JIN products are always "per the Approval Document", and when a wire is adopted, the Approval Document defines the model and the wire-diameter range.

1. First, understand what problem TIW solves (the one-sentence principle)

The value of triple insulated wire is that it builds the "reinforced insulation between primary and secondary" into the wire itself. A conventional small transformer relies on margin tape and interlayer tape to create creepage distance and clearance at both ends of the bobbin in order to separate the primary side from the secondary side; once you switch to a triple insulated wire that has been type-tested under the safety standards and evaluated as reinforced insulation, the winding-to-winding creepage and clearance can be reduced to almost zero, the tape and the margins are saved, winding-window space is freed up, and the high-frequency transformer can therefore be made smaller. In other words, TIW was born for primary-to-secondary safety isolation in high-frequency switching transformers.

So the question "do I need TIW?" can be reduced to one sentence: is my component a high-frequency isolation transformer that has to cross the primary-to-secondary safety barrier with reinforced insulation? If yes, TIW is usually a viable solution; if not, its strengths simply do not apply. Below, that sentence is broken down into three actionable criteria.

2. Locate your case in thirty seconds: three criteria decide whether to use it

Take any wound magnetic component, ask three questions in order, and you can sort it into "use / it depends / do not use":

• Criterion 1: Is there a primary-to-secondary safety barrier? What TIW solves is "reinforced insulation across the barrier". If the component is a single winding sitting in one potential domain—for example a PFC inductor, a filter choke, or the work coil of an induction heater—there is no primary and secondary to separate, and the reinforced-insulation value of TIW has nowhere to apply. This class runs on enamelled wire or litz wire; it is not TIW territory.
• Criterion 2: Is it a high-frequency switching transformer? TIW was designed for the miniaturization of high-frequency (switch-mode) transformers. Mains-frequency (50/60 Hz) distribution or isolation transformers belong to a different construction domain and are generally not a TIW application.
• Criterion 3: Is it the main power winding? The main power stage has to keep copper loss down at high frequency and high current density, and the industry mainstream there is litz wire (many strands sharing the current) and planar transformers (windings formed from multilayer PCB or copper foil). A single-strand, relatively fine TIW has limited current-carrying capacity and cannot carry the main winding of the main power stage; its place is low-to-medium-power isolation transformers.

Pass all three (barrier present, high frequency, not main power) = usually usable; fail either of the first two = usually not; the third is a matter of degree (not for main power, usable for small-power auxiliary / bias stages). Finally there is one threshold common to all cases: even when all three criteria are met, the transformer's actual working voltage, peak voltage and frequency, and the wire diameter you intend to use, must all fall within the rated ranges stated in the Approval Document; if any one of them falls outside, a separate evaluation is needed (this is one source of the "it depends" entries in the table below).

3. Selection map: end product → which stage → use / do not use / it depends

Lay out the common end products and look at which power stage or transformer inside them is the real question—in the same product, different stages can have opposite answers. All table values are defined per the Approval Document or by consulting sales:

• Medical equipment (patient-connected circuits) — Which internal power stage / transformer：Internal isolation transformer (high frequency, 2×MOPP path)；Use / do not use / it depends：Use；Per the Approval Document / further reading：Tied to TLW-BB / TLW-B7S, per the Approval Document; see Medical power supplies 2×MOPP
• Industrial / ITE equipment power supplies (SMPS) — Which internal power stage / transformer：Primary-to-secondary isolation transformer (flyback, LLC isolation stage, auxiliary stage)；Use / do not use / it depends：Use；Per the Approval Document / further reading：Annex J conditions per the Approval Document; see Selection guide
• Consumer electronics power supplies (AC adapters / power bricks) — Which internal power stage / transformer：Flyback isolation transformer；Use / do not use / it depends：Use；Per the Approval Document / further reading：Per the Approval Document
• Fast chargers (USB-PD / GaN adapters) — Which internal power stage / transformer：High-frequency flyback isolation transformer (miniaturized)；Use / do not use / it depends：Use；Per the Approval Document / further reading：Per the Approval Document; for the stranded type see TIW vs FIW vs enamelled wire
• LED drivers (isolated) — Which internal power stage / transformer：Isolation transformer；Use / do not use / it depends：Use；Per the Approval Document / further reading：Per the Approval Document (non-isolated types have no barrier; see Criterion 1)
• Gate drive (SiC / GaN power stages) — Which internal power stage / transformer：Wound gate-drive isolation transformer；Use / do not use / it depends：Use；Per the Approval Document / further reading：Per the Approval Document; see Data centers / AI servers
• Data-center / AI-server PSU — Which internal power stage / transformer：Small isolation transformers for auxiliary / standby / bias supplies；Use / do not use / it depends：Use；Per the Approval Document / further reading：Per the Approval Document; see Data centers / AI servers
• Data-center / AI-server PSU — Which internal power stage / transformer：Main power (PFC, main LLC, resonant inductor)；Use / do not use / it depends：Do not use；Per the Approval Document / further reading：Planar / litz; not a single-strand TIW category
• Automotive OBC / DC-DC — Which internal power stage / transformer：Main transformer；Use / do not use / it depends：Do not use；Per the Approval Document / further reading：Main power is litz / planar, and automotive qualification is a separate system; see Automotive OBC main transformer
• Automotive OBC / DC-DC — Which internal power stage / transformer：Tier-2 auxiliary / bias / gate-drive small transformers；Use / do not use / it depends：It depends；Per the Approval Document / further reading：The winding can use TIW, but the finished part must still pass automotive qualification; see Automotive OBC main transformer
• Mains-frequency distribution / isolation equipment (50/60 Hz) — Which internal power stage / transformer：Mains-frequency isolation / distribution transformer；Use / do not use / it depends：Do not use；Per the Approval Document / further reading：Not the high-frequency switching domain; different construction (Criterion 2)
• Induction heating equipment — Which internal power stage / transformer：Work coil；Use / do not use / it depends：Do not use；Per the Approval Document / further reading：No primary-to-secondary barrier; litz (Criterion 1)
• Power supplies of all kinds — Which internal power stage / transformer：Component-level inductors / chokes (PFC inductors, filter chokes)；Use / do not use / it depends：Do not use；Per the Approval Document / further reading：Single winding, one potential domain, no isolation barrier (Criterion 1)
• Any application — Which internal power stage / transformer：When working voltage / peak / frequency or wire diameter exceeds the rated range；Use / do not use / it depends：It depends；Per the Approval Document / further reading：Separate evaluation required, per the Approval Document

For any "use" cell in the table, the specific selectable models, wire diameters and withstand voltages are governed by the Approval Document; to confirm whether your own operating point falls within the conditions, consult the sales contact and have it defined per the Approval Document.

4. How to read the three verdicts: use, it depends, do not use

"Use"—primary-to-secondary reinforced insulation in high-frequency isolation transformers. This is TIW's home ground: medical, industrial / ITE, consumer power supplies, fast chargers, isolated LED drivers, gate drive, and server auxiliary / standby supplies—what they all share is a small isolation transformer that is "low-to-medium power, high frequency, and needs reinforced (or double) insulation across primary-to-secondary". In the DAH JIN product line, the four external models are TLW-B, TLW-BB, TLW-B7S and TLW-F: all four are listed within the IEC 62368-1 Annex J evaluation scope of VDE 40008834 Anlage 200 (specific conditions per the Approval Document); thermal class 130(B), with TLW-F being Class F (155 °C). The medical IEC 60601-1 path (2 MOOP / 2 MOPP, evaluated under Annex L) is tied only to TLW-BB and TLW-B7S, both of which are components of the DJ-130 (UL E318181) insulation system; adopting that system requires an Authorization Letter. For the mapping of each model and the certification chain, see TIW certification chain and Annex J / K crosswalk.

"It depends"—the barrier is there, but there is another threshold. The most typical case is automotive: in the Tier-2 auxiliary supply, bias and gate-drive small transformers of an OBC / DC-DC, the winding itself may well use TIW, but the finished magnetic component still has to pass automotive qualification (AEC-Q200 / ISO 16750 / LV124)—what the wire's Approval Document covers is the material (model and wire-diameter range), which does not mean the finished part has passed automotive qualification. The other "it depends" is an operating-point issue: even when the application is right, as soon as the working voltage / peak / frequency or the wire diameter exceeds the rated range in the Approval Document, a separate evaluation is required. In both cases, please consult sales and have it defined per the Approval Document rather than applying a blanket rule.

"Do not use"—TIW's strengths do not apply. Three situations: first, main power windings (automotive OBC main transformers, server main LLC and resonant inductors)—high current and high-frequency copper loss call for litz and planar; single-strand TIW is not the construction for this stage; second, the mains-frequency domain (50/60 Hz distribution / isolation transformers)—not the construction of a high-frequency switching transformer; third, no primary-to-secondary isolation barrier (component-level inductors, chokes, induction-heating work coils)—within a single potential domain there is no barrier to cross, so reinforced insulation does not come into play. The wire's thermal class and the system / finished-product thermal class are separate registrations and cannot substitute for each other; see Wire thermal class vs insulation-system thermal class.

DAH JIN is a wire manufacturer (not a trading company), producing at its own factory in Guiren, Tainan, Taiwan—made in Taiwan—and the manufacturing site stated in the UL file is this plant. For definitions of terms see the TIW glossary; for verifying UL 2353 see verify UL 2353.