ЛЭШО, ЛЭЛО, ЛЭПКО Wire — TU 16.К80-03-89, Markings and Equivalents

ЛЭШО is a Soviet high-frequency magnet wire (litz-wire grade, TU 16.К80-03-89). A multi-strand enamelled conductor with a single layer of fiber serving on top. Originally (1989, TU 16.К80-03-89) the serving was natural silk — hence the letter "Ш" (sh, for silk).

Today, in 2026, wire sold under the "ЛЭШО" designation has a polyester-fiber serving. No one uses natural silk anymore: it is expensive and hard to process. But the designation has stuck — too much active design documentation is tied to it.

Where it is used: windings of HF transformers, inductors and chokes. Repairs and series production under Soviet documentation. Thermal class — 105 °C. Cross-sections from fractions of a square millimeter to a few mm².

If the task is a replacement for existing design documentation, you need exactly ЛЭШО per TU 16.К80-03-89. If it is a new development, it makes sense to look at continuously transposed litz wire with 155–200 °C enamel, rectangular forming and modern coatings.

Decoding the abbreviation

The marking breaks down letter by letter:

• Л — litz wire (litzendraht). From the German Litzen (strands) and Draht (wire). A multi-strand wire in which each strand has its own insulation and all strands are twisted into a common bundle.
• Э — enamel insulation on the individual strands. Per clause 1.3.1 of the TU, ЛЭШО allows magnet wires with synthetic varnishes of class A (105 °C) or higher. The specific varnish is chosen by the plant.
• П in the middle of the designation — enamel with a polyurethane base. This raises the strand class from 105 °C to 120 °C. This is how ЛЭП (no serving, ПЭВТЛ-2), ЛЭПКО (polyurethane + nylon, ПЭВТЛ-1) and ЛЭПШД (polyurethane + double silk) are built. Without the letter "П", the enamel is conventional class A: ЛЭЛ, ЛЭШО, ЛЭШД, ЛЭЛО, ЛЭЛД.
• Ш — outer serving of silk. Per the original TU, natural silk. Today it is almost always polyester, less often nylon.
• Л as part of the serving (as in ЛЭЛО, ЛЭЛД) — lavsan (polyester).
• К — nylon (polyamide). In ЛЭПКО, a single-layer nylon serving over polyurethane enamel.
• О — single-layer serving. Д — double-layer.

As a result, the dual role of the letter "П" produces paired grades: ЛЭШД and ЛЭПШД (conventional enamel and polyurethane under a double silk serving); for single-layer nylon there is no version on conventional enamel in the TU, so ЛЭПКО is the only option. The family:

The minimum operating temperature per clause 1.1 of the TU is minus 60 °C. This covers the requirements of aviation, marine, and northern rail and ground equipment without separate approvals.

History of the standard: there is no GOST/OST for ЛЭШО

A common misconception is that ЛЭШО is governed by some OST or GOST. In fact, it is not. No GOST, active or repealed, governs the ЛЭШО grade as a separate item.

The only document is the industry specification TU 16.К80-03-89, "High-frequency magnet wires". It was approved by the USSR Ministry of the Electrical Engineering Industry in 1989. Decoding the number: "16" is the industry code of the Ministry of the Electrical Engineering Industry, "К80" is the cable-products index, "03-89" is the sequential number and year of approval.

The TU combines the whole family in one document — 10 grades: ЛЭЛ, ЛЭШО, ЛЭШД, ЛЭЛО, ЛЭЛД, ЛЭП, ЛЭПКО, ЛЭПШД, ЛЭТЛО, ЛЭНП. The current edition incorporates amendment No. 1 of Feb 1990 (К80.02-90) and amendment No. 2 of Jul 1996 (К80.07-96). ЛЭШД and ЛЭПШД are two distinct grades: with conventional class A enamel and with polyurethane class E enamel respectively, both with a double-layer silk serving.

These wires are produced by Pskovkabel, the Novomoskovsk plant Liparkabel, Rybinskkabel and a number of other plants — still to these very specifications. For defense procurement the TU is registered and undergoes certification per GOST RV 0015-002.

The OKP codes in Annex 2 are distributed unevenly: ЛЭЛ — 35 9153 0300, ЛЭП — 35 9154 0100, ЛЭТЛО — 35 9155 0700, ЛЭНП — 35 9157 0100. The rest (ЛЭЛО, ЛЭШО, ЛЭЛД, ЛЭПШД, ЛЭПКО) fall in group 35 9159.

Construction

In cross-section, ЛЭШО is simple: thin enamelled copper wire (the typical series per the TU is 0.05; 0.071; 0.10; 0.15; 0.20; 0.25 mm), many such wires twisted into a common bundle, with a fiber serving applied over it. The litz wire comes out round in cross-section, without any special forming.

An individual enamelled wire is usually ПЭВТЛ-1 or ПЭТВ-2 per GOST 26615 / GOST 7262 (polyurethane self-tinning or polyesterimide magnet wire). The fiber serving is applied with a lay that ensures dense coverage without gaps; the serving direction is usually opposite to the lay direction of the litz wire stranding.

The main constructional feature, important for understanding the limitations of ЛЭШО, is the absence of transposition. The stranding is ordinary, layered: the wires inside the bundle keep their fixed radial positions (central wires stay in the center, surface wires stay on the surface). When high-frequency alternating current flows, the individual wires interact differently with the coil's magnetic field, and proximity-effect losses are partly retained. A full continuously transposed litz wire with multi-stage interwoven stranding is a different construction, more complex to manufacture and outside the scope of TU 16.К80-03-89.

Marking: what "ЛЭШО 100×0.1" means

The standard marking has the form "ЛЭШО n×d", where n is the number of enamelled wires in the bundle and d is the diameter of each wire in millimeters. For example, "ЛЭШО 100×0.1" means 100 enamelled wires of 0.1 mm diameter, twisted into a common bundle, with a single-layer fiber serving on top.

The calculated copper cross-section follows directly: S = n · π · d² / 4. For ЛЭШО 100×0.1 this is 100 · 3.14 · 0.01 / 4 ≈ 0.785 mm². The actual overall diameter of the finished wire is always larger than the theoretical value — the thicknesses of the enamel (about 5–7 µm per wire) and the outer serving (about 30–60 µm) are added.

A few typical constructions per TU 16.К80-03-89 found on the Russian market:

The figures are taken from typical manufacturer catalogs (Pskovkabel, Liparkabel, distributors) and may vary from batch to batch within the TU tolerances. Exact values for a specific version are in the batch certificate.

Where it is used

The historical niche for ЛЭШО is windings of inductors and transformers operating at medium and high frequencies, where an ordinary single-strand wire has unacceptable losses due to the skin effect. Specific applications:

• Radio equipment. Tuned circuits of long- and medium-wave receivers and transmitters (tens to hundreds of kHz), intermediate-frequency coils, matching transformers. A huge fleet of Soviet military and civilian radio equipment — from the R-130 to consumer "Okean" receivers — is built on ЛЭШО and ЛЭПШД wire.
• Medium-frequency power electronics. High-frequency transformers and inductors in power supplies (PWM inverters, operating frequency 20–200 kHz), welding machines, ultrasonic generators, induction heating. ЛЭЛО and ЛЭШО are used in repairs and in series production under Soviet documentation.
• Laboratory and measurement equipment. Coils of reference generators, smoothing-filter chokes in measuring instruments, NMR setups.
• Military and space hardware where a reference to the TU is mandatory. Any radio-frequency winding built on domestic components, where the design documentation is tied to TU 16.К80-03-89 — it formally cannot be replaced with "litz wire of similar parameters"; exactly the wire per this TU is required, with the corresponding certificates and acceptance.

Why ЛЭШО is still in use

The main reason is documentation inertia. Over several decades, active Russian plants making radio, power and defense equipment have accumulated drawings, specifications and bills of purchased items in which ЛЭШО (or ЛЭПКО, ЛЭЛО) is explicitly written down with a specific marking per TU 16.К80-03-89. Replacing it with any other wire requires revising the design documentation, agreement with the customer, and sometimes repeat qualification testing of the product. For series products this is more expensive than continuing to buy "as before" — and this TU comes with a ready document package: batch quality certificate, QC acceptance report, certificate of conformity, and for defense applications, military acceptance. For any new TU this package has to be assembled from scratch.

The suppliers, too, are in place. Pskovkabel, Liparkabel, Rybinskkabel and a number of other plants produce the full range of ЛЭШО/ЛЭЛО/ЛЭПКО to these specifications. Production is almost always to order, with large minimum quantities and long lead times, which for series products with predictable demand is usually not a problem. For one-off repairs and single orders, a network of distributors and specialized small producers cutting from their own reels has historically served the need.

What is actually sold under the ЛЭШО designation

This is the key point rarely covered in catalogs. No one uses natural silk. Silk is expensive and hard to process: it delaminates, requires humidity conditioning during winding, and is uneven in diameter. For most tasks its properties are excessive. Plants long ago switched to multifilament polyester fiber (lavsan, PETP) with the same or better characteristics.

Legally, this point in the TU needs attention. Per clause 1.3.4 in the original 1989 edition, ЛЭШО and ЛЭПШД were allowed to use synthetic threads together with natural ones — but no more than 50 % of the quantity of natural threads. In other words, fully replacing silk with polyester is not covered by the letter of the original TU.

How it works in practice. Current batches are often fully polyester. This is either the result of later amendments to the TU (amendment No. 1 of 1990 and amendment No. 2 of 1996) or a deviation agreed with the consumer. If natural silk is strictly specified in the design documentation (biocompatibility in medical equipment, special climatic conditions), you should explicitly request a composition statement from the manufacturer. Some plants make a silk serving on a separate order, at a premium and with an extended lead time.

For most technical applications the difference between a silk and a polyester serving is negligible. Both are class A fiber insulation with close dielectric properties and comparable mechanics. The parameters of a coil wound with silk and with polyester ЛЭШО in reality differ by tenths of a percent — within the spread of the winding itself.

ЛЭЛО wire — differences from ЛЭШО

ЛЭЛО is the sibling of ЛЭШО with a factory polyester serving instead of silk. The same enamelled copper strand, the same diameters per TU 16.К80-03-89, the same thermal class A (105 °C). The only difference is the outer serving. In ЛЭШО it is natural silk (per the letter of the TU); in ЛЭЛО it is multifilament polyester fiber (lavsan, PETP). Hence the breakdown: Лitz wire + Эnamel + Лavsan + О for single-layer serving. The two-layer equivalent is ЛЭЛД.

The paradox: if modern "ЛЭШО" arrives from the plant with a polyester serving (and that is the case — see the previous section), then you are effectively buying ЛЭЛО marked as ЛЭШО. TU 16.К80-03-89 formally permits such a substitution by agreement with the customer, but legally these are different grades with different OKP codes.

When to order ЛЭЛО specifically, not ЛЭШО:

• ЛЭЛО is explicitly written in the design documentation — literal compliance with the documentation, no approvals needed.
• A guarantee of polyester fiber rather than silk is required — for coil impregnation, for better heat resistance under extreme conditions, for chemical resistance.
• Budget series products — ЛЭЛО is usually cheaper than ЛЭШО, because polyester is simpler to process than silk.
• Northern and Arctic versions — the minimum temperature of minus 60 °C per clause 1.1 of the TU is met equally, but polyester is more stable in moisture absorption.

The ЛЭЛО marking follows the same scheme as ЛЭШО: "Provod ЛЭЛО n×d ТУ 16.К80". For example: Provod ЛЭЛО 10×0,071 ТУ 16.К80 is 10 enamelled copper wires of 0.071 mm diameter, twisted into a bundle, with a single-layer polyester serving on top. The calculated cross-section is 0.0396 mm² per clause 1.2.3 of the TU.

Typical ЛЭЛО constructions per Table 1 of the TU cover cross-sections from ~0.01 mm² (3 wires of 0.063 mm) to ~5 mm² (the corresponding number of thick wires). The range of single-wire diameters is the standard series 0.050 / 0.063 / 0.071 / 0.100 / 0.180 / 0.200 / 0.224 / 0.315 / 0.500 mm. The minimum manufacturing length per clause 1.2.4 is 100 m for most cross-sections, 50 m for the large ones (2.43 and 4.25 mm²).

The ЛЭЛО equivalent in the DIADA catalog is the same as for ЛЭШО: Литц оПП1 (single-layer polypropylene serving) or Литц оА1 (single-layer Arselon aramid fiber) per TU ДСГТ.685660.019ТУ. Polypropylene is closer in properties to the lavsan of ЛЭЛО than silk is, so the transition is more "native". In addition: genuine multi-stage transposition, class F (155 °C) enamel instead of A (105 °C), lower temperature of minus 70 °C, tight tolerances. See the section "Modern equivalents" below for details.

Limitations of ЛЭШО for new designs

ЛЭШО is a wire for the technologies and tasks of 1989. It fills its niche. But for 2026 designs it has several weak spots.

Thermal class

ЛЭШО itself is class A (105 °C). This is set by both the serving and the enamel. Other grades in the family have higher classes: ЛЭП and ЛЭПКО — E (120 °C), ЛЭТЛО — B (130 °C), ЛЭНП — F (155 °C). But these are already different grades with different coatings.

Modern magnet wires outside the family — ПЭТВ-2, ПЭТ-200-2 — provide 155 and 200 °C. For power transformers at 100–200 kHz with high current density, the difference in class translates into tens of percent of winding density and into years of service life. If a coil design assumes a 90 °C regime at a 105 °C rating, the margin is only 15 °C — critical under deviations from the design regime. In most cases of replacing ЛЭШО the point is precisely to raise the class from 105 °C to at least 155 °C.

Packing geometry

ЛЭШО is produced only in a round cross-section. There is no rectangular forming for the grade itself in the TU. The family does include a separate grade with a rectangular cross-section — ЛЭНП (clause 1.2.1, Table 3 of the TU). But this is a narrow assortment: class F only, large cross-sections only, from 11.19 to 56.52 mm², ПЭТ-155 enamel with no fiber serving. For typical tasks that need a rectangular ЛЭШО equivalent at 0.5–6 mm² with a serving, ЛЭНП does not fit.

When round ЛЭШО is packed tightly into the rectangular window of a transformer bobbin, wedge-shaped voids remain between turns. The actual window fill factor is about 70–75 %. Continuously transposed litz wire with rectangular forming ("square litz wire") gives 85–90 %. A gain of up to 20 % in winding density. At the same inductance and number of turns — smaller core size, lower mass, better heat distribution.

Rectangular forming is a standard option in specialized specifications, for example TU ДСГТ.685660.019ТУ (DIADA Design Bureau). There it is available for any construction in any series with no cross-section restrictions — the "Пр" index in the grade (ЛитцПр).

The loophole in the TU: parallel laying instead of stranding is no longer litz wire

The main thing about genuine ЛЭШО is not even the absence of transposition. Clause 1.3 of TU 16.К80-03-89 contains an exception that is rarely noticed:

"By agreement with the consumer, the conductor of grades ЛЭШО, ЛЭЛО, ЛЭШД, ЛЭЛД and ЛЭПКО may be made from wire of 0.05; 0.071 and 0.10 mm diameter with up to 16 wires inclusive from enamelled wires laid in parallel."

What this means in practice. The very word "litzendraht" (German Litzendraht — interwoven wire) implies twisting individual enamelled strands into a common bundle while changing their radial position. Without stranding it is no longer litz wire, just an ordinary parallel multi-strand wire. Marking it "ЛЭШО" is a formal violation of the etymology: the letter "Л" in the marking means precisely "litz wire" = stranded. By the letter of the TU, it is permitted. By physics, it is a different product.

The skin effect and proximity effect in a bundle laid in parallel work the same as in a single solid conductor of equivalent cross-section. At tens and hundreds of kHz, such "ЛЭШО" offers no loss benefit at all — it is equivalent to a single thick wire of the same copper cross-section. No suppression of the surface effects litz wire was invented for.

This loophole exists because stranding thin wires (0.05–0.1 mm) into a proper bundle is a technologically complex and expensive operation: a special strander, low speed, risk of breakage. Parallel laying is several times simpler and cheaper, and for most tasks where HF operation is not critical, customers accepted it. And they still do — the exception is in the TU, while the order specification in most design documentation does not close it.

Coil Q factor: how catastrophic it is

Take ЛЭШО 16×0.1 on the tuned circuit of a long-wave or medium-wave receiver, operating frequency 200 kHz. The equivalent copper cross-section is about 0.126 mm², the equivalent bundle diameter as a solid is on the order of 0.4 mm. The copper skin depth at 200 kHz is δ ≈ 0.15 mm, and the ratio d/δ ≈ 2.7 — this is the zone of strong proximity effect.

In genuine continuously transposed litz wire, each wire passes through all radial positions over one stranding lay length, and F_R at this frequency stays around 1.1–1.3 with a properly chosen strand diameter. In parallel-laid "ЛЭШО" 16×0.1, the peripheral wires carry all the current while the central ones "sleep" — F_R rises to 2.5–4. Accordingly:

• Coil Q at 200 kHz with proper continuously transposed litz wire is on the order of 400–500.
• Coil Q at 200 kHz with parallel-laid "ЛЭШО" 16×0.1 is on the order of 100–150.

A drop in Q factor by 3–5 times. For a radio receiver — a loss of adjacent-channel selectivity by 1–2 orders of magnitude. For induction heating — a several-fold rise in losses and heating of the wire itself. For a transformer in an SMPS — tens of percent of excess heat that must be removed somehow. And all of this is formally within the letter of the original TU.

What to write in the order specification

If you are buying ЛЭШО / ЛЭЛО / ЛЭШД / ЛЭЛД / ЛЭПКО for an HF winding, it makes sense to state explicitly in the order specification:

"Conductor stranded, not parallel-laid. Use of the clause 1.3 exception of TU 16.К80-03-89 is not permitted."

Without this line, by the letter of the TU the manufacturer has the right to supply the parallel version if the number of wires is ≤ 16. In practice, few write this in the design documentation — and the customer gets something other than what "litz wire" implies. This is a pure loophole, known to the plants but rarely known to the winding engineer.

In DIADA equivalents per TU ДСГТ.685660.019ТУ this exception simply does not exist: any construction in any series is a genuine multi-stage transposed stranding, with no right to parallel laying. This is fixed in the TU itself as a mandatory requirement for the conductor.

In continuously transposed litz wire, each wire successively passes through all radial positions over one stranding lay length — from the center to the edge and back. This is transposition. It really reduces proximity-effect losses, especially above 50–100 kHz.

Qualitatively, the picture is as follows. At low frequencies (up to tens of kHz) the difference between ЛЭШО and continuously transposed litz wire is small. At hundreds of kHz to megahertz, losses in ordinary ЛЭШО grow due to incomplete utilization of the cross-section. In transposed wire with a properly chosen strand diameter, losses stay flat over a wide band. The optimal diameter of a single wire for a given frequency and coil geometry is calculated using the formula of Charles Sullivan of Dartmouth College. The same formula determines the frequency at which the use of ЛЭШО becomes suboptimal.

Tolerances

Here 16.К80 is inconsistent. The tolerances on electrical resistance in Tables 1–3 of the TU are tight — on the order of ±0.1–0.2 % of the calculated value. For a magnet wire this is quite a modern level.

The tolerance on the overall diameter over the fiber serving, however, is noticeably wider. Per clause 1.3.6 and Table 4 of the TU, an increase in the diameter over the insulation is allowed:

• up to 15 % for thin cross-sections (0.0196–0.1068 mm²)
• up to 10 % for medium ones (0.110–0.475 mm²)
• up to 5 % for large ones (0.550–4.25 mm²)

For precision tasks this spread may turn out to be excessively wide. For example, HF transformers for Qi-standard wireless power transfer require an inductance tolerance of ±2 %. Then you need either batch selection or a switch to stricter modern specifications.

Equivalents on the Russian market

Continuously transposed litz wire per TU ДСГТ.685660.019ТУ (TU 27.32.11-019-59596873-2025) — DIADA Design Bureau. Series 0.071/0.1/0.15/0.2/0.25 mm. Self-tinning enamel ПЭВТЛ-2 to class F (155 °C). For elevated temperatures — ПЭТ-200-2 to 200 °C.

The conductor construction is genuine transposition. Stranding with random positioning of the conductors: each wire changes its position from the center to the periphery of the bundle along the length of the wire. The resistance-increase factor relative to the theoretical value is no more than 1.03 for round wire, 1.05 for rectangular.

Outer coating, by choice: bare; polypropylene serving (1 or 2 layers — оПП1/оПП2); Arselon serving (оА1/оА2); polypropylene or Arselon braid (хПП, хА); PET, PTFE (Ф-4ЭО) or polyimide films; combined coatings. Rectangular forming is the "Пр" index. A 5-year warranty, 25-year service life, operating range from minus 70 to plus 155 °C (or 200 °C for the 200 index).

Direct grade correspondence:

The direct answer to "what to replace ЛЭШО with" is Литц оПП1. A single-layer polypropylene-fiber serving. Compared with the original ЛЭШО:

• class F (155 °C) instead of A (105 °C)
• lower temperature of minus 70 °C instead of minus 60 °C
• modern enamel ПЭВТЛ-2
• genuine transposition instead of layered stranding

Polypropylene is technologically more convenient than natural silk. It is also more resistant to oils and climate than polyester, which is used in the commercial version of ЛЭШО at other plants.

And the main thing. The new TU has a fundamentally wider range of coatings than the 16.К80 family. The old TU is limited to fiber (natural silk, polyester, nylon) and a single polyester braid in ЛЭТЛО. It has no films and no extruded insulation at all.

TU ДСГТ.685660.019ТУ adds to the fiber options:

• PET film (Литц ПЭТ, ПЭПЭТ-155-М). Breakdown voltage 1000 V. A smooth surface, low friction in the winding. In demand for precision windings.
• PTFE (fluoroplastic) film Ф-4ЭО (Литц Ф, ПЭФ-155-М and Литц 200 Ф, ПЭФ-200-М). Breakdown voltage 3000 V. Up to 200 °C. Resistant to oils and most industrial environments.
• Polyimide film (Литц ПИ, ПЭПИ-155-М and Литц 200 ПИ, ПЭПИ-200-М). Breakdown voltage 3500 V — the best in the line. For high-voltage transformers and space hardware.
• Extruded polyethylene jacket over PTFE (Литц фПЭ, ПЭКФлПЭ-А-М). Breakdown voltage 5000 V. A waterproof version. For especially critical applications.
• Extruded polyurethane jacket (made to order). More flexible than polyethylene. More resistant to oils, fuels and UV. Operating range down to minus 40 °C. For moving cable systems, cable carriers and robotic applications.
• Combined coatings (PTFE + polypropylene or Arselon). They combine the electrical properties of films with the mechanical protection of fiber.

This gives the engineer a tool that Soviet specifications lacked. With ЛЭШО you can make a functionally equivalent Литц оПП1. Or you can directly address tasks that ЛЭШО was never suited for: high-voltage windings, transformers in oil-filled enclosures, products for high humidity and aggressive environments.

A couple more options on the market:

• ЛЭТЛО per 16.К80-03-89 — increased heat resistance. ПЭТВ-2 enamel, class B (130 °C), a polyester braid. This is a version within the same original TU but with a more heat-resistant enamel. Available from Liparkabel and other manufacturers.
• Imported litz wire (Elektrisola, Pack Litz Wire, New England Wire). High thermal class, a wide choice of coatings, tight tolerances. In 2026, imports mean long lead times and difficulties with calculations and certification.

ЛЭШО → DIADA grade correspondence table

Direct correspondence by number of wires and diameter does not mean 1:1 in electrical parameters. Continuously transposed litz wire has lower AC resistance at the same frequency for an equal copper cross-section. The overall diameter is usually smaller thanks to tighter stranding. But for replacement geometry and the calculation of initial coil parameters, the table below gives an exact correspondence to the real catalog constructions of the 0.1 mm series:

The standard 0.1 mm series at DIADA Design Bureau starts at 63×0.1 and runs through 128, 190, 255, 315, 372, 440, 500, 570, 630, 700, 750 strands and on up to 2560. That is 40 standard constructions in total. For thin cross-sections (up to 50 strands), equivalents are produced as made-to-order items — in the DIADA catalog 78 made-to-order constructions have already been manufactured and listed against individual requirements.

The full series with calculated parameters is on the page /en/constructions/0-1/. For the 0.071, 0.15, 0.2, 0.25 mm series the correspondence is built on the same logic. The nearest standard construction by copper cross-section is selected. For non-standard parameters, a made-to-order version.

When ЛЭШО can and cannot be replaced

Can be replaced with continuously transposed litz wire

• New designs where the design documentation has not yet been approved — no formal ties.
• Repair and refurbishment of equipment without a mandatory reference to a specific TU in the operating documentation (consumer radio equipment, non-critical lab equipment, single items for in-house use).
• Reverse engineering of old equipment to improve parameters (upgrading a transformer by replacing round ЛЭШО with square litz wire to reduce size).
• Products for the civilian market with no certification to Soviet standards.

Cannot be replaced without customer agreement and revision of the design documentation

• Defense procurement with military acceptance, where the bill of components explicitly states ЛЭШО wire with a marking and a reference to TU 16.К80-03-89. Replacement requires a decision by the chief designer, agreement with the government quality representative, and sometimes repeat qualification testing.
• Products for the nuclear industry, aviation and space tied to industry standards — even if everything looks similar, a change of the normative reference requires a separate procedure.
• Service repair of equipment whose warranty requires the use of exclusively original materials per the factory specification.
• Any case where the wire's batch certificate is attached to the product certificate and checked at acceptance.

In borderline cases (the design documentation allows "ЛЭШО or equivalent") a written request to the product developer is needed, with a justification of equivalence — a parameter comparison table, a loss calculation, a measurement report if any were made.

How to select an equivalent for a ЛЭШО marking

To select an equivalent for a specific marking you need: the number of wires and their diameter (n×d), the required thermal class (105 °C, 130 °C, 155 °C, higher), the type of outer coating (single- or double-layer fiber, film, braid, combined), the operating frequency of the coil or transformer, the copper cross-section (if a full geometric replacement matters), the batch length, and the desired lead times. If an original batch certificate or a fragment of the original wire is available, that speeds up selection: it can be used to identify the exact construction even with an erased marking.

DIADA Design Bureau produces continuously transposed litz wire in small batches to individual requirements, including as a replacement for constructions per TU 16.К80-03-89. The minimum batch is from 30 meters and the lead time is up to 20 working days. The form for submitting a marking and selecting an equivalent is on the "ЛЭШО equivalent" page.

Frequently asked questions

Is modern ЛЭШО with a polyester serving compatible with repairs under Soviet documentation?

In most cases, yes, provided the design documentation has no explicit requirement for natural silk. TU 16.К80-03-89 permits substitution of the serving material subject to agreement with the customer, and in practice the whole market switched to polyester long ago. If the specification strictly states "natural silk serving", you either place a separate order with the manufacturer for the silk version or obtain written approval of the substitution.

What documents are supplied with ЛЭШО wire?

The standard package is a batch quality certificate (stating the marking, cross-section, diameter, resistance, length, OKPD2 code) and a certificate of conformity (a declaration for civilian use; for defense applications, military acceptance with an entry in the data sheet). Optionally, a dielectric breakdown test report and separate material certificates.

What is the minimum batch and lead time for ЛЭШО from Russian manufacturers?

Per clause 1.2.4 of the TU the minimum manufacturing length is 100 m for ЛЭЛ, ЛЭШО, ЛЭПШД, ЛЭЛО, ЛЭЛД, ЛЭП and ЛЭПКО. For the large cross-sections 2.43 and 4.25 mm² — 50 m. For ЛЭТЛО — 200 m. In other words, one spool per the TU is at least 100 m of wire. A batch smaller than a spool is not produced with a certificate at all.

Large plants (Pskovkabel, Liparkabel and similar) work to order only. Minimum quantities are tens of kilograms per item, which in running meters for thin constructions means kilometers. Lead times are usually 4–8 weeks, longer for complex and rare diameters. As a rule there is no stock of specialized items. Distributors and small producers serve the popular ЛЭШО/ЛЭЛО grades in small batches.

At DIADA Design Bureau, continuously transposed litz wire as an equivalent has a minimum batch from 30 m with no tie to the TU manufacturing length. Delivery is 2–4 weeks depending on the complexity of the construction.

How do coil losses differ between ЛЭШО and continuously transposed litz wire?

It depends on which ЛЭШО exactly. For stranded ЛЭШО at frequencies up to tens of kHz the difference is within a few percent. At hundreds of kHz it is 10–30 %, noticeable in coil heating. At megahertz the difference can be several-fold.

But if the supplier invoked the clause 1.3 exception of TU 16.К80-03-89 and assembled the conductor from enamelled wires laid in parallel (formally allowed for grades up to 16 wires), such "ЛЭШО" physically behaves like a solid wire of the same cross-section. Then the difference from genuine continuously transposed litz wire is several-fold: coil Q at 200 kHz drops by 3–5 times, and losses rise several-fold. See the section "Coil Q factor" for details.

Without an explicit clause in the order specification, parallel laying can be told from stranding only by examining a cross-section of the wire.

Can ЛЭШО be soldered without stripping the enamel?

Yes, if the magnet wire is self-tinning (grade ПЭВТЛ-1) — it is designed for tinning in a solder bath at 320–390 °C for 20–30 seconds. At this temperature the enamel breaks down and the copper wets with solder. If the enamel is not self-tinning (ПЭТВ-2 and similar), preliminary stripping is required, either mechanically with a scalpel or chemically (with solvents or special pastes). The outer fiber serving is always removed before tinning.

What is the difference between ЛЭШО and ЛЭПКО?

ЛЭШО is a single layer of natural silk serving (or polyester in practice in modern production) over a strand with conventional class A enamel (105 °C). ЛЭПКО is a single layer of nylon (polyamide) serving over a strand with polyurethane enamel ПЭВТЛ-1, class E (120 °C). The key difference is the letter "П" in the middle: it denotes polyurethane varnish. Nylon has slightly better chemical resistance; silk/polyester impregnates better with varnishes during subsequent coil impregnation.

How does ЛЭЛО differ from ЛЭШО, and what to replace it with?

ЛЭЛО is ЛЭШО with a factory polyester serving (lavsan, PETP) instead of natural silk. The enamelled copper strand, the diameters and thermal class A (105 °C) are the same as for ЛЭШО per TU 16.К80-03-89. The breakdown: Лitz wire + Эnamel + Лavsan + О for single-layer. The two-layer equivalent is ЛЭЛД. ЛЭЛО can be replaced by the same DIADA continuously transposed litz wire — Литц оПП1 (polypropylene serving) or Литц оА1 (Arselon). In addition: class F (155 °C) instead of A, lower temperature of minus 70 °C, tight tolerances and genuine multi-stage transposition. See the section "ЛЭЛО wire" above for details.

What is the difference between ЛЭШД and ЛЭПШД?

These are two distinct grades in the same TU 16.К80-03-89, both with a double-layer silk serving. ЛЭШД has conventional class A enamel, thermal class A (105 °C). ЛЭПШД has polyurethane-based enamel (the letter "П"), class E (120 °C). When replaced by a modern equivalent both map to Литц оПП2 (double-layer polypropylene serving) per TU ДСГТ.685660.019ТУ — it offers class F and genuine transposition, which covers the requirements of both original grades.