LED Drivers: Where an Isolated Flyback Still Justifies Triple Insulated Wire (TIW)

This article is written for power-supply and magnetics design engineers, and for buyers, working on LED drivers. You may be sourcing winding wire for the transformer inside an LED driver and wondering whether to use triple insulated wire (TIW). Let us be candid first: not every LED driver justifies TIW — a non-isolated design (buck / boost) has no transformer barrier at all, so there is nothing for TIW to do; and for indoor low-voltage, low-power isolated designs, conventional construction is often sufficient. Where TIW genuinely earns its premium is the isolated flyback in which "reinforced isolation is a safety prerequisite" — above all outdoor high-voltage / high-power designs and UL Class 2 designs. This article draws that line clearly: worth it / it depends / not worth it. All DAH JIN product values are "per the Approval Document".

1. First Question: Does Your LED Driver Have Electrical Isolation?

TIW only comes into play when there is a primary (mains-connected) ↔ secondary isolation barrier to be crossed. So the first step is to identify the topology:

• Isolated: typically a flyback or forward topology, using a transformer to separate the primary side from the secondary side. Among these, flyback is the isolated topology most commonly adopted for Class 2 LED drivers — simple structure, reasonable cost, capable of power factor correction (PFC), with electrical isolation between primary and secondary.
• Non-isolated: typically buck or boost, using a single inductor with the input and output directly connected electrically; there is no transformer, and even the feedback optocoupler can be omitted. Efficiency is higher (industry figures are commonly around 90–95%, versus about 85–88% for isolated designs), cost is lower, and it suits indoor luminaires with sealed, non-conductive enclosures.

The conclusion is direct: a non-isolated design has no transformer barrier, so TIW does not enter the picture. Only in isolated topologies — where primary ↔ secondary reinforced isolation must be built — does TIW come up for discussion.

2. What TIW Solves in an Isolated Flyback

In an isolated flyback, the primary side is connected to the mains, and the secondary side is usually SELV (Safety Extra Low Voltage; generally not exceeding 50 V AC or 120 V DC to earth). The SELV secondary must be separated from the high-voltage primary by double or reinforced insulation (or a protective screen).

This is precisely the reinforced isolation that TIW is designed for: it is a single, relatively fine enamelled conductor with three layers of insulation — one wire that on its own satisfies Reinforced insulation, eliminating the interlayer insulating tape and margins that a conventional transformer requires, and letting the transformer be built smaller. This is where TIW's value lies.

But "valuable" does not mean "worth it in every design". How much electrical stress this reinforced isolation sees, and whether that tape and that space need to be saved, is what decides whether TIW pays off. The next two sections cover the zones where the premium is most clearly justified.

3. Where the Premium Is Justified (1): UL Class 2 Isolated Designs

First, a term that is often conflated — "Class 2" and "Class II" are read the same way but are two different things:

• UL / NEC "Class 2" is about output power limitation (UL 1310 / NEC Article 725): output voltage ≤ 60 V DC (dry locations) or ≤ 30 V (wet locations), current < 5 A, power < 100 W. Its safety logic is to keep the output energy within a range unlikely to cause electric shock or fire.
• IEC "Class II" is about internal construction and insulation: double or reinforced insulation separates the user from live conductors, with no earth connection required (two-wire mains lead).

The whole safety premise of Class 2 is "limit the output energy to a safe range, and make sure primary ↔ secondary are genuinely separated". To convert the mains reliably into a power-limited SELV output, primary ↔ secondary reinforced isolation is the core. TIW implements this layer of Reinforced isolation cleanly with a single wire — exactly matching the crux of a Class 2 isolated design. Here, the TIW premium is justified.

4. Where the Premium Is Justified (2): Outdoor High-Voltage / High-Power

Outdoor LED drivers (street lights, high-bay fixtures, signage, etc.) are the other field where it pays. Their conditions are markedly harsher than indoor: input voltage commonly 90–305 V AC, power commonly tens to hundreds of watts (approaching a kilowatt at the top end), IP67 ingress protection, surge immunity often up to 10 kV, with an SELV output and compliance with luminaire safety standards such as EN 61347-1 / 61347-2-13.

Outdoor electrical stress is high — lightning surges, earth potential differences, humidity and temperature swings — which makes primary ↔ secondary galvanic isolation especially important. A higher input voltage and larger surge energy mean the withstand voltage and robustness of the reinforced isolation barrier carry more weight; using TIW here to build solid Reinforced isolation while keeping the transformer compact delivers clearly more value than in an indoor setting. Outdoor high-voltage / high-power is the second zone where the TIW premium is justified.

5. Where TIW Is Not Necessarily Needed (An Honest Line)

For the sake of honesty, the "not worth it" zones should also be stated clearly:

• Indoor non-isolated buck / boost: no transformer, no electrical isolation barrier — TIW simply has no use here.
• Indoor low-voltage, low-power isolated flyback: a conventional margin-wound / interlayer-tape transformer often already meets the requirement at low cost; when space is not tight, TIW is mostly a "structural convenience (miniaturization)" rather than a safety necessity — it depends.
• Designs that need only basic / functional insulation (not Reinforced): if the insulation level does not reach reinforced, TIW is not necessarily required.

• Outdoor high-voltage / high-power isolated flyback (street lights, high bay, signage) — Isolation barrier：Yes; high outdoor electrical stress, withstand voltage and robustness carry weight；Role of TIW：One wire achieves Reinforced, saving margins / tape；Worth it?：Worth it (premium justified)
• UL Class 2 isolated flyback (voltage- and current-limited SELV output) — Isolation barrier：Yes; reinforced isolation is a safety prerequisite；Role of TIW：Cleanly achieves Reinforced to the power-limited secondary；Worth it?：Worth it
• Indoor low-voltage, low-power isolated flyback — Isolation barrier：Yes, but conventional construction is often sufficient；Role of TIW：Mostly a structural convenience for miniaturization, not mandatory；Worth it?：It depends
• Indoor non-isolated buck / boost — Isolation barrier：No transformer, no electrical isolation；Role of TIW：No role to play；Worth it?：Not worth it (simply not applicable)

Note: for DAH JIN's four public models (TLW-B / TLW-BB / TLW-B7S / TLW-F), the model designation, wire diameter range and thermal class (Class B 130 °C / Class F 155 °C, etc.) are defined solely per the Approval Document; DAH JIN is the manufacturer (own plant in Guiren, Tainan, Taiwan; made in Taiwan), and externally the Approval Document prevails — please contact our sales team.

One last honest caveat concerns the standards framework: the LED driver itself falls under luminaire safety standards (e.g. IEC 61347 / UL 8750; Class 2 additionally under UL 1310), whereas the TIW Approval Document is based on UL 2353 / IEC 62368-1 Annex J (safety of ICT and audio/video equipment) and IEC 60601-1 (medical, per the Approval Document). The concept of Reinforced insulation is shared, but whether a given model's Approval Document can be applied directly to your luminaire safety design is still defined by the scope of the Approval Document and the safety baseline of that design — please confirm with our sales team. For the first step in selection (B 130 °C vs F 155 °C, etc.), see the selection guide; for the distinction between wire thermal class and system thermal class, see Wire thermal class vs insulation system thermal class.