Suggestion: Please, would you mention a context of those safety relays. There are various relays that are called safety relays depending on their function in circuitry.
See Allen-Bradley "Understanding the Machinery Directive"
Publication SHB-900 September 1997, and "Safety Products" Publication Safety-GC-001-A-US-P Septrmber 1999.
Suggestion: Please, notice that there are also safety relays used to separate various circuits in safety related circuits/designs including redundant trains, divisions, channels, etc.
Question: Are you referring to fail-safe scenarios, redundancies, switchovers, combinations of the above? All three (and others) can be used effectively in safety override circuits. As mentioned by others above, context is key. What's up? General knowledge, or do you have a specific application in mind?
