The ability of a switch grease used in a switch design to prevent contact surface wear is normally the primary goal. Wear debris can create two problems; it can inhibit current flow when the contact is closed, potentially increasing millivolt drop. When the contact is open, conductive debris has the potential to cause open circuit resistance problems.
It’s not always just contact surfaces that require lubricating in a switch design, there could be a damping requirement in the mechanical design; by damping we mean damping of movement/motion, noise and also improving the tactile feel of the switch – see damping grease articles. If damping is required, it may be prudent to try and use the same grease for contact surface lubrication and as a damping grease, most grease will give some level of damping.
The variety of electrical switch designs, application types and operating environments are such that it is difficult to offer simplistic advice on switch grease selection. Like all grease selection tasks, the selection of the most appropriate base oil and thickener is key. 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 application require grease that uses a lighter base oil viscosity. Of course any grease used should be inherently dielectric, we never recommend using a conductive grease on a switch application!
Grease for contacts that experience arcing. Because the temperatures reached when electric arcing occur are high enough to degrade any organic molecule, it’s a lubricant’s characteristic to ‘burn cleanly’ that is a huge advantage. The use of inappropriate grease on arcing contacts can lead to carbon deposits, resistance, heat and switch failure. Grease applied to any arcing contact should be formulated with base oil and thickeners that degrade without leaving carbon deposits on the contact surface. Advancements have been made over the years so we now have ‘clean burn’ formulations to help switch designers deal with arcing problems. Typically we consider a glycol based formulation to deal with switch arcing problems.
Non-burning switch grease technology. Grease that oxidises under arcing conditions can cause a problem for low load/low current applications. Clean burning glycol formulations are used to minimise carbon build up. The use of a perfluoropolyether grease that is dispersed in a non-flammable, ozone safe, fluorinated solvent is solution to be considered; these products leave a thin film of lubricant in place after the solvent has dispersed, ideal for low load/low current switch applications.
Grease for distribution switchgear. Switchgear will normally remain inactive for long periods of time. The grease will need to serve as protective barrier in addition to the lubricating task. The grease should be very stable over time, resistant to moisture (where relevant) and should not migrate away from the area of intended application. In some industrial switchgear applications, high temperatures may be induced by high current flow or high temperature conditions; for this reason the chosen grease will often need a wide temperature capability.
Now take a look at our overview of the switch grease range article.