Compared to conventional metal conductors, most greases are insulators. Even if it contains some conductive particles, such as zinc, copper, etc., the resistance difference is still quite large compared to the conductor.

2. How does the contact resistance of the switch come about?

Figure 1: a switch on, b switch closed, c open and off and time-top view

The surface of the switch is very smooth to see with the naked eye. When we place it under a microscope, the surface of the switch is quite rough and uneven. Therefore, under the influence of different contact forces, the effective contact area of the switch is only 0.01% to 1% of its surface area. (Figure 1a, 1b) This very small contact area determines the size of the contact resistance.
In many cases, a layer of metal oxides or plastic decomposing materials is often formed on the contact surface, increasing the contact resistance. This oxide layer is usually destroyed when the contact pressure is large enough or heat is enough to form. However, the heat generated can exacerbate micro-seismic corrosion, leading to a further increase in the contact resistance. In addition to the oxidation layer, the actual effective contact area left behind becomes a-spot (Figure 1c).
At the same time, in the continuous opening and closing of the switch process, due to friction and wear, in the absence of lubricants, the actual effective contact area will continue to decrease, directly reflected in the switch's contact resistance is rising, the final impact on the actual use of the switch.

3. Can conductive paste really reduce contact resistance?
As can be seen from Figure 1c, the actual effective contact area is formed by the plastic deformation of the protruding part of the switch surface, and the contact grease is usually filled in a concave place to form an inert environment on the switch surface to avoid oxidative corrosion. In the process of switching and closing, due to the reflux characteristics of the grease, an effective oil film is formed on the contact surface to avoid wear.
For conductive paste, because of the existence of some of its conductive particles, in the concave part, may form a certain conductive channel, because the contact resistance of the conductive paste is still much larger than the metal, so the conductive paste conductive efficiency is greatly reduced, but also will bring the problem of heat. At the same time, due to the presence of conductive particles, the insulation performance of the switch and anti-arc performance, will bring further impact.
Therefore, the comprehensive assessment, conductive paste will have some improvement on contact resistance, but at the same time will have a heating, as well as insulation performance aspects of the impact, is not particularly suitable for long-term use on the contact.

4. How to choose the right contact lubricant?
The choice of contact lubricants depends mainly on the media environment in which they are located, and for Crubourd, we have the following products for you to choose from.

The lubrication products for air media environments are:

• Kluberlectric KR 44-402
• ISOFLEX TOPAS NB 52

• BARRIERTA L 55/2
• BARRIERTA I EL-102