Switches

Grease for sliding electric switch contacts must meet similar demands as other mechanical sliding surfaces: film strength, appropriate low and high temperature fluid range, and stay-in-place capability. In particular, a switch grease’s ability to prevent wear is critical. Wear debris creates two problems. It can inhibit current flow when the contact is closed, increasing millivolt (mV) drop. When the contact is open, conductive wear debris can cause open circuit resistance (OCR) problems. In either case, switch performance is compromised. When selecting a switch grease, also note that the viscosity of the base oil should complement the contact force of the switch. Low current/low contact force applications require lighter base oils. High current/high contact force applications benefit from more viscous base oils.

Lubricants for arcing contacts.

Because the temperatures reached in an electric arc are sufficiently high to degrade any organic molecule, a lubricant’s tendency to “burn cleanly” is a definite advantage. Greases for arcing contacts should be formulated with fluids and thickeners that degrade with fewer by-products than traditional greases. A recent innovation is the addition of an additive that scavenges surface oxides to reduce contact resistance.

New non-burning switch lubricant technology.

Greases that oxidize under arcing conditions pose a special problem for low load/low current applications. Traditionally, cleaner burning glycols were used to minimize carbon build-up. A new approach to eliminating problems associated with oxidation is to use UniFlor™, non-burning perfluoropolyether-based greases. Dispersed in a non-flammable, ozone-safe, fluorinated solvent, these greases leave a thin film of lubricant, ideal for low load/low current applications. An additional benefit, this thin film does not attract dust and debris.

Lubricants for distribution switchgear.

Lubricants for distribution switchgear, which may remain unactuated for long periods, serve a protective as well as a lubricating role. They should be oxidatively stable over time, water-resistant, and non-migrating. Because high temperatures may be induced by high current flow or high-temperature industrial conditions, wide temperature capability can be important.

A note about damping greases.

Nye damping greases are widely used on the mechanical elements of many switch assemblies. They serve to reduce friction and wear, quiet detents, and give a smooth controlled “feel” to switch operation. See our application summary on Damping Greases for details.

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