The general-purpose 5, 10, and 20 amp relays that are the staple and mainstay of control panels everywhere are most often made with silver or silver-cadmium contacts. These are great as long as the energy passing through them when closed is high enough to generate a little arc when they open to help keep them clean. Low energy (less than 100 mA at 24 VDC) passing through such contacts for prolonged periods of time will cause oxides to form. These oxides are insulators, and they will eventually coat the contacts and prevent current from passing at all.

For low-energy applications, gold flashed or gold plated contacts should be used, such as the Model RY2SUAC24V relay available from Kele. Gold is very non-reactive and resists oxidation quite well. Another helper for low-level switching is contact geometry - bifurcated contacts (basically in the shape of a two-tined fork) provide multiple current paths for improved reliability.