Do I need a safety PLC, or will a safety relay do?

The risk assessment decides, not the budget and not the preference. But there is a practical dividing line. A safety relay is right when you have a small number of independent safety functions with simple logic. One or two E-stops, a guard interlock, a light curtain, each doing one thing. It is cheap, it is quick to wire, and its behaviour is obvious from the schematic. A safety controller starts to pay when: - You have more than roughly five safety functions, where the relay count and the wiring stop being simple. - The logic is conditional. Muting, zone control, different behaviour in setup mode versus production. - You need diagnostics. A relay tells you it has tripped; a controller tells you which channel, and that is the difference between a five minute fault find and an hour. - Safety data has to travel over a network to another cell. What does not change either way: the required performance level comes out of the risk assessment first, and then you choose hardware that achieves it. Both routes can reach PL e. Picking the hardware first and assessing afterwards is the wrong order and it is how projects end up rebuilding a panel.