Contact Material
According to the desired characteristics of the relay contact, very diverse materials, in particular precious metal alloys, are used.
In practice the contacts of a relay
operate at the most varied electrical loads with regard to voltage, current and power. It
must be noted that inductances in a switching circuit can create high overvoltages in the process disconnection whereas capacitances can cause make current spikes.
Even the effect of possible spark quenching and the connection of the control circuit (coil) to suppress cut-off voltage spikes affect the contact load (endurance).
To date, no universal material has been identified to cover the multitude of possible applications. From experience gathered over several years, the following assessment criteria are important to the manufacturer of contact materials as well as the developer and user of relays for the suitability of a
contact material:
- contact resistance (voltage drop)
- burn-up resistance
- creep of material
- welding susceptibility
According to these criteria, the most important contact materials and their typical characteristics can be classified in the application range with regard to current and voltage; see overview table of „characteristic features of contact materials" below.
All of the important contact materials are given in the overview table. As the load carrying capacity of the contacts and their endurance depend not only on the contact material but also on the structural features (e.g. on the contact force), the data for individual relay types cannot simply be transferred to
other structural forms.
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