This part of IEC 61810 covers test conditions and provisions for the evaluation of endurance tests using appropriate statistical methods to obtain reliability characteristics for relays. It should be used in conjunction with IEC 61649. This International Standard applies to electromechanical elementary relays considered as non-repaired items (i.e. items which are not repaired after failure), whenever a random sample of items is subjected to a test of cycles to failure (CTF). The lifetime of a relay is usually expressed in number of cycles. Therefore, whenever the terms time or duration are used in IEC 61649, this term should be understood to mean cycles . However, with a given frequency of operation, the number of cycles can be transformed into respective times (e.g. times to failure (TTF)). The failure criteria and the resulting characteristics of elementary relays describing their reliability in normal use are specified in this standard. A relay failure occurs when the specified failure criteria are met. As the failure rate for elementary relays cannot be considered as constant, particularly due to wear-out mechanisms, the times to failure of tested items typically show a Weibull distribution. This standard provides both numerical and graphical methods to calculate approximate values for the two-parameter Weibull distribution, as well as lower confidence limits and confirmation of reliability values with WeiBayes method. For electromechanical elementary relays where enhanced requirements for the verification of reliability apply, reliability test procedures are specified in IEC 61810-2-1. In particular when electromechanical elementary relays are intended to be incorporated in safety-related control systems of machinery in accordance with IEC 62061 and ISO 13849-1, IEC 61810-2-1 defines procedures for the manufacturer to reveal B10d values. NOTE Electromechanical elementary relays with forcibly guided (mechanically linked) contacts according to IEC 61810-3 offer the possibility of a high diagnostic coverage according to 4.5.3 of ISO 13849-1:2006.