EXAR® Motor Lead Cable - Benefits of Material Science
EXAR irradiation crosslinked polyolefin technology was originally developed in 1972. Since then, it has been an industry standard for motor and transformer lead wire. EXAR was originally developed for motor OEM’s who needed high-performance yet lower cost lead wires capable of surviving the rigors of both motor manufacture and rugged in-service applications.
Manufacturing the motor is a harsh process. The entire stator unit including the lead wires are immersed in insulating varnish followed immediately by an oven bake curing process, where the temperatures can be in excess of the motor rating itself. These bake cycles are 4-12 hours at temperatures over 275°F. Some processes include vacuum and pressure cycles as well. Either method can cause the wire insulation to fail, exposing the conductor, which results in expensive rework.
Electric motors are used in a wide spectrum of diverse applications. Many of these applications demand that the unit resist exposure to fluids, dirt and debris, vibration, and high temperatures. The lead wire insulation is often directly exposed to these harsh environments and must be robust in order to withstand the effects of such exposure.
VARNISH RELEASE
Insulating varnish is designed to adhere to most surfaces, including lead wire insulation. Best-in-class motor lead products have superior resistance to these varnishes. They incorporate materials and processing technology to help the wire resist cracking and allow the cured varnish to release easily from the surface of the wire after the varnish bake process is complete and the leads have cooled.
Below are pictures of three common motor lead cables after a varnish bake test consisting of 3 x 45 minute cycles at 385F.
EXAR: UL 3289 Irradiated XLPO
Cured resin flakes off, insulation
does not crack.
EPDM Rubber: UL 3340
Cured resin sticking to wire,
multiple cracks in insulation
Silicone rubber: UL 3604
Cured resin sticking to wire,
multiple cracks in insulation
SPACE SAVINGS
UL and CSA require different insulation thicknesses depending on the cable type and insulation material. Among common motor lead wires, irradiated polyethylene’s have some of the thinnest insulation requirements due to their toughness and durability.
Although the individual wire diameter difference may not be dramatic, when compounded across multiple leads inside of a motor, bundled leads of EXAR are significantly smaller, resulting in smaller cable penetration dimensions through motor and transformer housings.
Some motor designs simply don’t have room for thicker cables, in which case irradiated XLPE’s are among the only cost-effective options.
Cable Under Irradiation Beam
INSULATION TOUGHNESS
A thin wire insulation is of no use unless it is tough enough to withstand the rigors of the application. Material durability is a critical part of the criteria for determining lead wire insulation thickness. EXAR was specifically developed to be a tough material, capable of handling harsh environments and rugged use. The result is a cable insulation much tougher than other common motor lead materials such as Silicone and EPDM rubbers.
Tensile strength is a UL required test that measures the force required to rupture the insulation. EXAR has a tensile strength more than double that of silicone, and almost 1.5x that of EPDM.
|
Product (8AWG UL Samples)
|
Nom. Tensile
|
|---|---|
|
EXAR SFX-OR
(UL 3289)
|
2,520
|
|
Silicone
(UL 3213)
|
1,055
|
|
EPDM
(UL 3340)
|
1,423
|
FLUID RESISTANCE
Not all motor lead cables are fluid resistant. In most applications, motor lead wires are not exposed to fluids. However, some applications can have significant exposure via spray or even submersion. For example, motors for hydraulic systems often are immersed in hydraulic fluid, and submersible pump motors may be exposed to water, brine, or other fluids.
Resistance to fluids allows cables to be used in multiple applications. EXAR 150 and EXAR SFX-OR have UL approval for use in oil exposure up to 60°C. Because of this feature, EXAR is used in hydraulic systems where the cables are immersed in hydraulic oil.
Below is a table of tensile and elongation values from UL 758 oil resistance testing. The UL requirement is 50% retention of original values. Actual retained tensile value is a discrete reflection of the strength of the insulation after oil exposure.
UL 758 Oil Immersion Test In Submersible Pump Insulating Oil (1)
| Product
(8AWG UL Samples) |
Wall Thickness | Initial Tensile
(psi) |
% Retained Tensile
(50% min req.) |
Initial Elongation
(psi) |
Retained Elongation
(50% min req.) |
Pass/Fail |
|---|---|---|---|---|---|---|
| EXAR SFX-OR
(UL 3289) |
0.046 | 2,520 | 1,411 (56%) | 305.6 | 228 (75.4%) | Pass |
| EPDM
(UL 3340) |
0.086 | 1,423 | 540 (38.5%) | 380.4 | 144 (38%) | Fail |
| Silicone
(UL 3213) |
0.060 | 1,055 | 886 (84.2%) | 325.0 | 299 (92.5%) | Pass |
(1) Due to differences in fluid properties, Champlain strongly recommends testing cables in your specific fluid at operating temperature to determine compatibility. Champlain can assist with this evaluation.