High Voltage Silicone Wire 3–60 kV, UL 3239 and UL 10475

High Voltage Silicone Wire for X-Ray, Imaging and Electrostatic Equipment

Above about 3 kV a lead wire stops being a conductor with insulation on it and becomes an insulation system with a conductor in the middle. On UL 3239 the copper barely changes across the whole range while the silicone wall grows from 0.50 mm at 3 kV to 3.11 mm at 60 kV — a 20 AWG lead goes from 1.91 mm to 7.20 mm across the finished diameter without gaining a single strand. If a 60 kV lead will not pass through your gland, that is why.

Silicone is the standard insulation here for two reasons: it holds a high dielectric strength in a wall you can still bend, and it does not carbonise. TEBAOFLEX builds UL 3239 from 28 AWG to 10 AWG, and UL 10475 — the same construction in larger conductors — from 8 AWG to 2 AWG.

• Suitable for: X-ray and medical imaging, photomultiplier and image-intensifier supplies, cathode-ray and display equipment, electrostatic precipitators and coating plant, neon and sign transformers, HV DC test and laboratory equipment.
• Confirm before ordering: kV class, AWG size, temperature grade, colour and reel length.
• Choose another construction when: the duty is engine or burner ignition rather than a DC supply lead — a jacketed ignition wire is built for that, and we make those separately.

Not sure whether you need a high-voltage lead or an ignition wire? Compare in the high temperature wire selection matrix, or see the wider range under High Temperature Cables.

Construction

Two elements and no third. A stranded annealed tinned copper conductor, and a silicone rubber wall whose thickness is set entirely by the voltage class you order. There is no jacket, no screen and no braid — the silicone is the whole insulation system, and that is deliberate.

1. Conductor: annealed tinned copper, stranded or solid. On UL 3239 the standard construction is 7 strands across the range — 7/0.127 mm at 28 AWG through 7/0.50 mm at 16 AWG. UL 10475 carries the larger conductors from 8 AWG to 2 AWG.
2. Insulation: silicone rubber, wall selected by voltage class: 0.50 mm at 3 kV, 0.70 at 6 kV, 1.00 at 10 kV, 1.30 at 20 kV, 1.70 at 30 kV, 2.12 at 40 kV, 2.51 at 50 kV and 3.11 mm at 60 kV.
3. No jacket, no shield: the standard construction is unjacketed and unscreened. If your application needs a screened HV lead, say so — that is a different build.
4. Colours: standard colour range with custom colours to order.

Why the wall grows and the copper does not

Current rating and voltage rating are independent problems. The conductor is sized by the current the circuit draws, which on an X-ray or photomultiplier supply is usually milliamps — so 22 or 20 AWG is plenty even at 60 kV. The insulation is sized by the field it has to hold off. That is why the range looks the way it does: the same 20 AWG conductor appears in every voltage class from 3 kV to 60 kV, and only the wall changes. Specifying a bigger conductor does not buy you more voltage.

What the finished diameter does to your design

Across the 20 AWG row the outside diameter runs 1.91, 2.31, 2.91, 3.51, 4.31, 5.20, 6.00 and 7.20 mm as the class climbs. A 60 kV lead is nearly four times the diameter of the 3 kV version of the same wire. Glands, grommets, bend radii, cable ties, routing channels and connector backshells all have to be chosen from the finished figure in the table below — and a bundle of six 60 kV leads is a very different object from a bundle of six 10 kV leads.

Why silicone rather than a fluoropolymer

At these wall thicknesses stiffness decides whether the wire can be installed at all, and silicone stays bendable where a 3 mm fluoropolymer wall would not. Silicone also fails gracefully: it burns to a non-conductive silica ash rather than a carbon track, which matters more at 60 kV than at 600 V because a carbon track is a ready-made flashover path.

Applications

High voltage silicone wire is a DC supply lead inside equipment. It runs from a high-voltage power supply or transformer to the thing being fed — a tube, an electrode, a plate — and it is chosen by the field it has to hold off rather than by the current it carries.

Equipment and duty this wire is built for

• X-ray and medical imaging — tube supply leads inside generators and scanners.
• Photomultiplier tubes and image intensifiers — low-current, very high-voltage feeds where insulation integrity is the whole design problem.
• Cathode-ray and display equipment — anode leads in legacy and specialist display hardware.
• Electrostatic precipitators — electrode feeds in flue gas cleaning plant, which is also a hot environment.
• Electrostatic coating and powder plant — gun and grid supply leads.
• Neon and sign transformers — secondary leads on illuminated signage.
• HV DC test and laboratory equipment — test sets, insulation testers, HV benches.
• Ignition circuits, furnaces, heaters and dryers — where the lead is a supply feed rather than a jacketed ignition wire.

High voltage lead wire is not ignition wire

These two get confused constantly and they are different products. An HV lead wire like UL 3239 is unjacketed, chosen by kV class, and spends its life inside a cabinet feeding a tube or an electrode. An ignition wire is jacketed or braided, built to survive an engine bay or a burner front, and rated for the pulse duty of a spark circuit rather than a steady DC field. If the wire fires a spark, you want an ignition construction — see our 7/10 kV silicone ignition cable, the Style 3304 and 3573 10 kV ignition wire with a fiberglass braid and jacket, or the ECS-HT VDE 1.8/3.0 kV ignition wire.

Where this wire is the wrong answer

• You need a screen or a jacket — the standard construction has neither. Screened HV leads are a separate build.
• Spark and pulse ignition duty — use a jacketed ignition construction.
• High current at high voltage — this is a lead wire for low-current supplies. Power at medium voltage is a cable problem, not a lead-wire problem.
• Continuous flexing or reeling — at a 3 mm wall the wire is stiff and is not built for repeated movement.
• Fixed building installation — AWM appliance wiring material carries no such listing.

Cross-referencing an existing lead

HV lead wire is usually marked with the style and a kV figure, but the figure on the print is sometimes a test voltage rather than the working class. Send a photograph of the marking together with the measured outside diameter and the conductor size, and we will work back to the voltage class from the wall thickness — the diameter table below makes that unambiguous.

Specifications

One construction, eight voltage classes. The conductor is chosen by current, the wall by kV, and the finished diameter falls out of the two together.

High voltage silicone wire styles at a glance

Temperature note: style 3239 is supplied at 150 °C and at 200 °C depending on the silicone compound, and both are current in the market. The style number alone does not settle it — state the temperature grade you need on the enquiry.

Insulation wall by voltage class

Dimensions and Electrical Data — UL 3239

Nominal overall diameter in mm for every size and every voltage class. Read down a column to size a gland; read across a row to see what the class costs you in space.

Sizes 14 to 10 AWG are built to order in the same classes; 8 to 2 AWG move to style 10475. Standard put-up is 610 m (2,000 ft) on the smaller sizes and classes, dropping to 305 m (1,000 ft) as the diameter climbs.

All values are nominal and subject to normal manufacturing tolerance. Nominal diameters vary slightly between producers; treat this table as a planning envelope rather than a drawing dimension, and confirm the final size before ordering.

Other properties

Standards

Standards, test methods and compliance references that apply to high voltage silicone wire in these UL AWM styles.

Working voltage, test voltage and the number on the print

Three different figures get printed on high-voltage lead wire and they are not interchangeable. The voltage class is what the wall is designed around and what you order by. The test voltage is a factory proof figure, always higher. And a peak or impulse figure, where quoted, describes transient capability, not continuous duty. If a drawing gives you a bare kV number with no qualifier, the safest reading is to treat it as the working class and confirm — specifying a class from a test-voltage figure is how a lead ends up two classes thinner than the design intended.

What the style number does not settle

UL 3239 covers a range of constructions rather than one. The style fixes the material and the general category; it does not fix the voltage class, and it does not fix the temperature grade — product is sold under this style at both 150 °C and 200 °C. An enquiry that gives only the style number cannot be quoted. Give us the style, the kV class, the AWG and the temperature grade and it can.

TEBAOFLEX certification

Jiangsu TEBAOFLEX Special Cable Co., Ltd holds UL certificate UL-US-2449012-0 and cUL certificate UL-CA-2437036-0, both dated 27 December 2024 under report E542560-20241225, and VDE certificate 40060055 dated 28 March 2025. These are company-level certifications. Send the exact style, class and size you intend to order and we will confirm the approval scope that applies to it before you commit, and issue the test documentation with the shipment.

Documentation supplied with an order

• Construction drawing and dimensional data for the agreed class and size
• Routine test records for the production batch, including the applied voltage test
• Certificate of conformity referencing the agreed standards
• Reel and packing list with marking details

For the scope of a specific standard, consult the issuing body directly — for example the International Electrotechnical Commission or UL Solutions.