Section 5 - Evaluating Standard Constructions

From the many material options available for insulation, braiding and jacketing of high-temperature wire, four basic non-asbestos materials are dominant: silicone rubber compounds, fluoropolymers used in extruded and taped insulation, mica and glass. These should be evaluated for possible simplification of selection decisions and cost reductions. Where many different types of high-temperature wire products are ordinarily stocked for varying applications, a "highest-necessary" standard can be established for such critical performance variables as voltage, temperature rating, current-carrying capacity and ambient conditions. Although a "highest-necessary" wire selection may mean slight over-specification for some applications, the marginally higher cost can be easily absorbed by the resulting reductions in production changeovers, purchasing administration and stocking costs. Standard wire constructions can be conveniently reviewed in four groups in conjunction with their approval status at Underwriters' Laboratories and Canadian Standards Association.

Performance to 200 C

Freedom- 200	Braided Silicone

For the highest necessary threshold of 200 C, a common choice is extruded Teflon* FEP, used alone, or general-purpose braided or braidless silicone rubber. Each has a broad range of excellent properties, both electrical and physical. In addition, their uniform outer diameters and easy stripping help ease assembly of appliances and other high-temperature electrical products.

Performance to 250 C

Freedom- 250	TGE/TGT
TGGE TGGT and Trimflex	Braidless Silicone

For 250 C service, PFA fluoropolymer or premium silicone rubber are available. When physical damage is unlikely, as in enclosed appliances, the increased toughness of premium silicone permits its use without the protection of glass braid.

PFA fluoropolymer can also be used without protection because it is tough and cut resistant. When severe abrasion or other abuse is expected, a TGGT wire is often specified. It features Teflon PTFE tape as primary insulation, a secondary layer of served glass and an outer layer of Teflon-impregnated glass braid.

The relatively small outside diameter of TGGT Unistrip^TM 250 helps meet close manufacturing tolerances for mechanically "light-duty" applications.

Performance to 350 C

Ultralead- 350

For small-appliance and industrial applications, a 350 C construction of mica tape with a layer of glass serving protected by a tough, specially treated outer glass braid offers a cost-effective alternative when 250 C-rated constructions are below specification and more costly 450 C-rated wires are above specification. For ease of interchangeability with 250 C wires, or as a "highest-necessary" replacement, Ultralead^TM 350 is constructed in comparable outside diameters and available in both 300- and 600-volt electrical ratings. Thus it can be installed in the same amount of space and yet meet the higher temperature rating.

Performance to 450 C

MGE/MGT

For 450 C service, a mica-based insulation composite is often used as a "highest-necessary" selection. Mica tapes, supported by a glass scrim backing, form the primary insulation. These tapes are further protected by glass braid treated with a silicone enamel or a Teflon dispersion finish. MGE and MGT wires are ideal for extreme high-temperature applications, such as commercial food-service equipment, heat-treating furnaces, kilns, and heaters, with voltage ranging from 300 to 600 V.

MGT UNISTRIP^TM 450

UL and CSA certified for 450 C, 300 or 600 volts. Excellent cutting/stripping uncommon to all other 450 C wires, and easily processed in large volume on automatic equipment. Plus improved dimensional consistency and uniformity. Applications include commercial food service equipment, major and small appliances, heating elements, and hot surface igniters.

NOTE: * Teflon is a registered trademark of E.I. DuPont de Nemours & Company.
^TM Unistrip is a trademark of Radix Wire Company.