IEC 62912-2015 pdf download.Railway applications – Direct current signalling monostable relays of type N and type C.
4 Classification The requirements of the various categories of signalling relays required to guarantee installation with the degree of reliability and safety desirable for operating purposes, depend on the functions to be fulfilled by the relays and the type of circuit with which they are to be used. Bearing in mind these characteristics, a distinction may be made between the following types of signalling relays:
• Type N (non-proved relays) Relays themselves fulfilling all the safety conditions without the aid of other relays or without control of operations in the circuit.
• Type C (proved relays) Relays for which the safety conditions are guaranteed by control of operations in the circuit.
5 Essential requirements of the relays and their construction
5.1 Generic requirements for signalling relays
5.1 .1 Forcibly guided (mechanically linked) contacts Signalling relays shall be equipped with forcibly guided (mechanically linked) contacts. The forcibly guided (mechanically linked) contacts shall be designed in such a way that it is ensured by mechanical means that make and break contacts can never be in the closed position simultaneously. If one of the make contacts is closed, none of the break contacts is closed. If one of the break contacts remains closed, none of the make contacts closes (assuming that nominal power conditions apply – see also 5.6.2). Operation of forcibly guided (linked) contacts means that if, for example, any given make contact fails to open and the relay is de- energised, none of the break contacts closes.
The same principle applies to the failure-to- open of a break contact with energisation of the relay, i.e. in this case, no make contact shall close (IEC 61 81 0-3).
5.1 .2 Forcibly guided (mechanically linked) operation The efficiency of forcibly guided (mechanically linked) contact operation shall be maintained as long as the relay operates, even when beyond the specified endurance. This applies both to loaded and unloaded contacts. Forcibly guided (mechanically linked) operation shall be maintained even if individual parts of the relay fail. Under such circumstances, it is irrelevant whether this failure is due to wear or breakage. Use of change-over contacts is permitted for signalling relays in safety-relevant circuits.
5.2 Specific requirements
5.2.1 Relays of type N
5.2.1 .1 These shall be characterised by their non-weldable make contact points, through the use of a suitable contact point material (for example, silver-carbon for which there is no risk of welding above a certain percentage of carbon), or by the introduction of special constructional conditions preventing risks of welding of the contact points (for example, fusing, contacts in series).
5.2.1 .2 The relays shall open the make contacts by falling of the armature under its own weight, when the current is interrupted in the coil. NOTE The relays that open the make contacts by only the force of return springs when the current is interrupted in the coil are not included in this subclause.
5.2.1 .3 The relays may also be equipped with return springs. These return springs shall only be used to increase the contact force of break contacts and ensure that the required time parameters for the armature to fall are met. They shall not be used for the opening of the make contacts.
5.2.2 Relays of type C This type of relay shall be that the falling of the armature of the relay is proved during operation; for this reason, no special qualities of non-weldability are required for the material that contact points are made of.IEC 62912 pdf download.