Basic safety principles - Well-tried safety principles - well tried components

In addition to functional requirements that are defined in functional safety standards, the machinery directive integrates the following requirements that are design rules and sometimes manufacturing technological choices.

ISO 13849-2:2012 : Safety of machinery - Safety-related parts of control systems - Part 2: Validation, defines for these Basic safety principles and Well-tried safety principles for :different kind of technologies in its annexes

Annex A (informative) Validation tools for mechanical systems

Annex B (informative) Validation tools for pneumatic systems
Annex C (informative) Validation tools for hydraulic systems
Annex D (informative) Validation tools for electrical systems
Annex E (informative) Example of validation of fault behaviour and diagnostic means

For example for electrical systems Annex D these tables defines :

Table D.1 — Basic safety principles. These principles are the one that defined the safety at high level such as 

• Use of de-energization principle - whose objective is to suppress the residua energy in order to suppress the dangerous movement.
• Protection against unexpected startup
• ...

Table D.2 — Well-tried safety principles - These principle are more linked to technology and take into account the knowledge of safety devices regarding their characteristics 

• "Positively mechanically linked contacts" and the remark gives information for the use of positively mechanically linked contacts for, e.g. monitoring function in Category 2, 3, and 4 systems (that complies to EN 50205, IEC 60947-4-1: Annex F, IEC 60947-5-1, Annex L).
• Positive mode actuation - Direct action is transmitted by the shape (...) with no elastic elements, (...) that comply to some standards such as ISO 14119, ISO 12100.
• ...

Table D.3 — Well-tried components - that table gives well tried components for which some failures do not have to be taken into account if they comply to a rule or a spécific requirement of one standard such as :

• Switch with positive mode actuation (direct opening action) that complies to the requirements of IEC 60947-5-1:2003, Annex K
• ...

The following tables gives for all classic components somes rules where it is possible not to take into account some failures. For example for a PCB, Table D.5 - Short circuit between two adjacent tracks/pads can be excluded if the design of the PCB complies with the requirements of  IEC 60664-1 for distances greater than (...) with pollution degree (...)

Table D.4 — Faults and fault exclusions — Conductors/cables.

Table D.5 — Faults and fault exclusions — Printed circuit boards/assemblies

Table D.6 — (...)

Table D.21 — Faults and fault exclusions — Electronic components — Programmable and/or complex integrated circuits

Similar tables exists for :

Annex A (informative) Validation tools for mechanical systems
Annex B (informative) Validation tools for pneumatic systems
Annex C (informative) Validation tools for hydraulic systems
Annex D (informative) Validation tools for electrical systems
Annex E (informative) Example of validation of fault behaviour and diagnostic means