What is the failure rate P level on the datasheet of the mechanical relay?

Contact resistance may be a problem when opening and closing microloads.
If a high contact resistance value is accidentally generated, it may be recovered by the subsequent operation.
In addition, contact resistance may increase due to generation of contact coating.

Whether or not the contact resistance value is considered a failure depends on whether or not a problem occurs in the circuit. For this reason, the failure criteria for the contact resistance of relays are specified only in the initial value, and the failure rate is expressed using the P level (reference value) as a guideline for the minimum applied load.

The failure rate is the rate at which a failure occurs within a unit time (number of operations) when the relay is opened and closed continuously at the specified test type and load.
This value can vary depending on the frequency of opening and closing, the environment, and the level of reliability you expect. Be sure to test the actual equipment under actual operating conditions.

When using at a microload level, the reliability may vary depending on the contact material and contact method. Consider signal (communication) relays that emphasize contact reliability.