Winding Tapes — Glass Fibre & PTFE

The Three Tape Types — At a Glance

Each tape type serves a distinct role in transformer and motor assembly. Understanding which tape does which job prevents the wrong material being applied at the wrong stage of winding — a mistake that can compromise dielectric performance or thermal life.

Full Technical Specifications

What Is Glass Fibre Winding Tape?

Glass fibre winding tape — also referred to as glass cloth tape, fibre glass winding tape, or glass fabric tape — is a woven tape produced from electrical-grade E-glass fibre yarns. The woven construction gives the tape a combination of properties that makes it indispensable in transformer and motor winding: high tensile strength in both the machine and cross direction, dimensional stability at elevated temperatures, and a porous open-weave structure that allows varnish or epoxy resin to penetrate and cure completely when the wound coil undergoes impregnation.

The glass fibre base material itself is rated well above 200°C, which means the thermal class of the finished tape system is determined entirely by the binder or impregnating varnish applied to it. A dry glass tape impregnated with Class F polyester varnish yields a Class F system; the same tape impregnated with Class H silicone or epoxy resin yields a Class H system. This gives winding engineers flexibility to achieve the required thermal class by choosing the appropriate varnish at the impregnation stage, without changing the tape itself.

What Is PTFE Insulation Tape?

PTFE tape used in electrical applications is not the same product as the plumber's thread-seal tape sold in hardware stores. Electrical-grade PTFE insulation tape is a precision-slit, skived (shaved) film of virgin PTFE with a controlled thickness of 0.075 mm to 0.20 mm, tested for dielectric strength (typically ≥ 60 kV/mm) and dimensional consistency across the full roll length.

PTFE is a fluoropolymer with an exceptionally low dielectric constant (approximately 2.1), near-zero moisture absorption, and a continuous service temperature of 260°C — properties that no other common tape material approaches simultaneously. It is non-adhesive: when applied with 50% overlap, successive layers of PTFE fuse to each other under the tension of winding, creating a continuous seamless wrap that will not unravel or delaminate during subsequent handling.

ACC Insulations distributes electrical-grade PTFE tape sourced from qualified manufacturers. We supply by the roll to transformer winding shops, motor winding houses, aerospace wiring harness assemblers, and high-frequency inductor manufacturers across India.

What Is Lacing Tape?

Lacing tape — also called winding lace, cable lacing tape, or binding tape — is a narrow, non-elastic flat tape used to tie, bundle, and secure winding leads, coil terminations, and cable harnesses inside transformers, motors, generators, and switchgear panels. It is not a primary insulation material — its role is mechanical: keeping winding leads routed correctly, preventing conductor movement during vibration, and maintaining the tidy lead geometry that assembly drawings require.

Lacing tapes are available in three base materials, each suited to different thermal class and oil compatibility requirements. Cotton lacing tape is the traditional choice for Class A and Class B transformers; glass fibre lacing tape is specified for Class F and H designs or for oil-filled applications where cotton would degrade; polyester lacing tape offers a balance of mechanical strength and moderate temperature resistance for Class F motor winding harness work.

Key Properties of Glass Fibre Winding Tape

How Glass Fibre Winding Tape Is Applied

In a transformer winding shop, glass fibre tape is applied at several stages of the coil assembly process. Understanding each stage helps specify the correct tape grade:

• Over bare conductor sections: Where a transformer winding lead is left bare (uninsulated copper or aluminium), glass fibre tape is hand-wound over the conductor to provide the required dielectric spacing before the lead passes through a bushing or connection terminal. A varnished grade is preferred here to maximise dielectric strength per millimetre of tape.
• Inter-layer insulation reinforcement: Between winding layers in disc windings and layer windings, glass fibre tape provides additional mechanical reinforcement on top of the kraft paper or DDP inter-layer insulation — particularly at winding ends where paper edges are exposed and vulnerable to partial discharge initiation.
• Motor end-turn binding: In random-wound stator coils, the winding end-turns projecting beyond the core stack are bound with glass fibre tape to prevent conductor movement under the centrifugal forces of motor operation, vibration, and thermal cycling. The tape holds the end-turns in a compact, structurally sound geometry before VPI or dip-and-bake impregnation locks them permanently.
• Covering the wound coil before impregnation: The full outer surface of a wound transformer coil is often covered with one or two layers of glass fibre tape before entering the varnish dipping tank or VPI vessel. This outer wrap provides structural integrity during handling, prevents the coil winding from unravelling before impregnation, and gives the varnish a textured outer surface to adhere to.
• Dry tape for VPI applications: Where the coil will undergo vacuum pressure impregnation (VPI), dry (unimpregnated) glass fibre tape is deliberately specified — it allows the VPI resin to penetrate through the tape into the underlying winding. Pre-varnished tape would block resin penetration and create a void-rich interface between the tape and the conductor.

Applications

Glass Fibre Tape vs PTFE Tape — Which to Specify?

Transformer winding engineers and motor rewinders are often asked to choose between glass fibre tape and PTFE tape for conductor insulation or winding work. The decision depends on the functional requirement:

Why Winding Shops Choose ACC Insulations

Frequently Asked Questions

What is glass fibre winding tape used for?

Glass fibre winding tape is used for hand-taping transformer coils, binding motor end-turns, providing inter-layer insulation reinforcement between winding sections, and covering winding leads where they exit the coil. It is also applied as an outer wrap over the complete wound coil before varnish dipping or vacuum pressure impregnation (VPI). It can be applied dry (for VPI applications, where the resin must penetrate through the tape) or pre-impregnated with varnish or epoxy resin for applications where additional dielectric strength is required from the tape itself.

What is the difference between glass fibre tape and PTFE tape for electrical insulation?

Glass fibre winding tape is a woven fabric tape providing both mechanical reinforcement and electrical insulation — preferred for hand-taping coils, binding end-turns, and reinforcing winding structures where tensile strength is required. It is VPI-compatible because the open weave allows resin to flow through it during impregnation.

PTFE tape is a non-woven film tape made from polytetrafluoroethylene — it provides extremely high dielectric strength (≥ 60 kV/mm), chemical resistance, and a temperature rating of 260°C, but offers no structural reinforcement. It is ideal for wrapping individual conductors and insulating lead wires. PTFE is non-wettable and is therefore not suitable for VPI processes — it blocks resin penetration. Choose glass fibre tape for coil-level taping; choose PTFE tape for conductor-level wrapping and high-temperature lead insulation.

Is ACC Insulations a manufacturer or distributor of PTFE tapes?

ACC Insulations is a distributor of electrical grade PTFE insulation tapes. We source PTFE tapes from qualified manufacturers and supply them by the roll to transformer winding shops, motor manufacturers, and electrical equipment assemblers across India. For glass fibre winding tapes and lacing tapes, we operate as both component supplier and distributor, with in-house precision slitting to custom widths. All products — whether manufactured or distributed — are verified as electrical grade before supply.

What widths of glass fibre winding tape does ACC Insulations supply?

We supply glass fibre winding tapes in standard widths of 12 mm, 19 mm, 25 mm, 38 mm, and 50 mm, all available from stock. Custom widths are slit in-house from master rolls using our precision slitting equipment — there is no minimum order restriction on custom widths, and we can match any width required by your winding machine or hand-taping process. Contact our sales team with your width, thickness, impregnation requirement (dry, varnished, or epoxy), and thermal class, and we will confirm availability and lead time.

Can glass fibre winding tape be used without varnish or resin impregnation?

Yes — dry (unimpregnated) glass fibre tape is specifically preferred for coils that will subsequently undergo vacuum pressure impregnation (VPI). The open-weave structure allows the VPI resin to fully penetrate through the tape into the underlying winding, producing a void-free impregnated system. Pre-varnished tape should not be used for VPI because the cured varnish layer blocks resin penetration, leaving an inadequately impregnated interface between the tape and conductor layers. Dry tape is also used for mechanical binding work where the tape will be covered by a subsequent impregnation cycle. Pre-impregnated tapes (polyester varnish or epoxy) are the right choice when the tape must provide dielectric performance in its own right, without relying on a subsequent impregnation process.

What is lacing tape and where is it used in transformer winding?

Lacing tape is a narrow flat tape — typically 6 mm, 9 mm, or 12 mm wide — used to tie and secure winding leads, bind coil ends, and organise cable harnesses inside transformers, motors, and switchgear. It is a mechanical restraint material rather than a primary insulation material: it keeps conductor leads routed correctly, prevents movement during vibration, and maintains the tidy geometry that assembly drawings require. In transformer winding, lacing tape is used to bind the winding lead exits at the top of the coil, tie the outer insulation wrap in place before impregnation, and secure connection harnesses between the LV and HV winding terminals.

What thermal class are the winding tapes supplied by ACC Insulations?

Glass fibre winding tapes are available in Class F (155°C) and Class H (180°C) grades depending on the impregnating varnish or resin applied. The glass fibre base material itself is rated well above 200°C; the thermal class of the finished system is determined by the binder. PTFE insulation tapes are rated to 260°C continuous — exceeding Class H. Lacing tapes are available in Class B (130°C), F (155°C), and H (180°C) grades. Please specify your required thermal class when placing an enquiry so we can confirm the correct tape grade for your application.