Glass Fibre Covered Wire
Rectangular BS 4799 Part 2 / 1972
Round BS 4779 Part 1 / 1972

Insulated glass covered wire is a practical approach to the problem of reliable high temperature magnet wire insulation. Glass fibre magnet wire is manufactured by serving a combination of glass fibres on a bare or film coated conductor. The glass fibres are then insulated with a suitable varnish and heated to bond the fibres to the conductor and to each other. This system produces an insulation of extreme toughness and abrasion resistance. Transwire manufactures single or double wraps of varnished glass over round and shaped conductors, bare or film insulated. Transwire varnished glass magnet wire is recommended for Class B, F or H equipment dependant on which type of insulation varnish is applied.Generally speaking glass insulated magnet wire can be used extensively in electrical machinery where high temperatures, vibration and excessive moisture conditions are encountered.

INCREASE IN DIMENSIONS DUE TO THE COVERING

NOTE: The maximum increase in dimensions may be amended when IEC Recommendation is published

1 Adhesion and Flexibility

1.1 As received. Samples of the glass-covered conductor shall be bent through 180° round a mandrel having a diameter 10 times the bare width of the conductor when it is bent on edge, or 10 times the bare thickness when it is on the flat. Separate samples shall be bent, one on edge and one on flat and when so tested the covering shall not open sufficiently to expose the bare conductor to view, when examined under diffused light by normal eyesight. There shall be no appreciable loosening of the insulation.

1.2 After heating. Samples which have been heated for 16 h in an oven at a temperature of 150°C to 155°C and then allowed to cool to room temperature, shall pass the test for flexibility and adherence specified in 1.1.

2 Breakdown voltage. The wire shall meet the requirement of 2.1 and 2.2. when tested at room temperature and at elevated temperature respectively.

2.1. Tests at room temperature. Samples shall be subjected to a breakdown voltage test by the method described in Appendix E. At least four of the five places tested shall not break down at a voltage less than the appropriate value in Table 4, and the fifth at a voltage not less than 50% of the required value.

2.2. Test at elevated temperature. When tested by the method described in Appendix E, at the rated temperature, at least four of the five samples tested shall not break down at a voltage less than the appropriate value in Table 4, and the fifth at a voltage not less than 50% of the required value.

Paper Application Methods

The insulating paper is wrapped firmly, closely, evenly and continuously round the wire.

Construction, unless otherwise specified, is typically one of the following alternatives:

1. All papers are wrapped in the same direction with the inner paper applied with a butt lap. Successive papers are applied with an advance of 30-50% over the underlying paper with a maximum gap of (.79mm).
2. Papers are applied with butt intercalation in the following manners:
   1. 2 papers - double butt intercalation - advance 40-60%
   2. 3 papers - triple butt intercalation - advance 28-38%
3. Papers are lapped in the following manners:
   1. One paper applied with 47-49% overlap - equivalent to two papers.
   2. One paper applied with 64-66% overlap - equivalent to three papers.
   3. Two papers each applied in the one of the above manners.

The taping angle (measured between the paper and longitudinal axis of the wire) is normally in the range of 45-60 degrees, however, certain unusual sizes and constructions may necessitate angles outside this range.

Insulated Wire Dimensions

When build is specified only by number of papers there is no requirement for finished dimensions, however constructions of types (a) and (b) contain the specified number of papers, and type (c) shall contain the equivalent number of specified papers.

When build is specified the tolerances of the paper additions to conductor thickness and width shall be as specified in table P1.

Flexibility

Conductors under (6.35mm) thickness shall withstand 180 degrees flatwise bending around a mandrel 6 times the conductor thickness in both directions without exposure of the conductor.

Conductors (6.35mm) and over in thickness shall withstand 180 degrees flatwise bending around a mandrel ten times the conductor thickness in both directions without exposure of the conductor.

Nomex *

Nomex type 410 aramid paper is an aromatic polyamide product which combines high temperature durability with the high mechanical and electrical properties required for an outstanding insulating material.

Type 410 retains good electrical properties in the presence of moisture. For example, its di-electric strength, is essentially constant for paper conditioned at 0 and 95% relative humidity.

Nomex maintains its excellent combination of electrical and mechanical properties over long periods at elevated temperatures.

In laboratory and field tests with refrigeration systems, refrigerant gas samples and compressor oil samples have not shown any significant contamination or degradation resulting from the use of type 410 paper in the system.

The Nomex used on TW. magnet wire is (.05mm) in thickness. For single paper insulation the tape is 49% to 66% lapped. For multiple papers (two or three) the tapes are intercalated.

TW. Nomex insulated magnet wire is recommended for use in up to 200°C equipment for copper conductors.

It will meet the requirement of NEMA SPECIFICATIONS MW-60/MW-61.

* Du Pont Company registered trademark.

Kapton * Polyimide
Films (Types H & F)

Kapton Polyimide film maintains its excellent physical, electrical and mechanical properties over a wide temperature range. Kapton type H has been used successfully in applications where the temperatures have been as low as - 269°C and as high as 400°C. There is no known organic solvent for the film and it is infusible and flame resistant.

Many applications for Kapton Polyimide film are based on the fact that the excellent electrical properties for Kapton, such as dielectric strength and dissipation factor, remain nearly constant over a wide range of temperatures and frequencies. Others make use of the film's radiation resistance or chemical resistance at elevated temperatures.

Because Kapton type H has no melting point. Dupont combines Teflon ** Fep-fluorocarbon resin with the polyimide to produce Kapton type F. The primary purpose of the Teflon Fep is to provide a heat-sealable surface on the tough non-melting polyimide base film (i.e. Kapton type F may be heat bonded to itself without the use of adhesives - the resulting insulation behaves more like a film than a wrap). In addition, the coating of Teflon Fep improves the chemical resistance of the composite film, especially to bases and concentrated acids and reduces the rate of moisture permeability and oxidative decomposition. In almost all cases, this combination of Kapton type H with Teflon Fep gives a film whose properties are arithmetic averages of the two components.

Applications for Kapton type F are based on the excellent high temperature electrical and mechanical properties of thin gauge Kapton type H plus the complete seal, moisture protection and flexibility imparted by the Teflon Fep.

* Du Pont Company registered trademark.