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General-purpose Relay Topic: The Most Effective Type for Protecting Contacts

FAQ No. FAQ02804

Question

Choosing from among CR elements, diodes, varistors, and other kinds of surge suppressor elements, which is the most effective for protecting contacts?

Answer

For a DC load, a diode is generally the most effective, and the next most effective is CR elements. For an AC load, a varistor or CR elements are the most effective.

Typical Surge Suppressor Examples:

Typical Surge Suppressor Examples

Typical Surge Suppressor Examples (Continued)

Do not use the following kind of surge suppressor application.

This circuit effectively suppresses arcs when the contacts are OFF. Capacity is stored in C when the contacts are open. Consequently, when the contacts are ON again, short-circuited current from the capacitance may cause contact weld.

It is commonly believed that it is more difficult to switch DC inductive loads than resistive loads, but the performance can be improved to about the same level as resistive loads by using a surge suppressor.

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