Control Systems Safety Relays????


Thread Starter


Can anyone elaborate on the requirements of Category 3 (ISO 13849-1/EN 954-1)? As a small integration shop, I am trying to ensure that the design of our control systems meet safety requirements in both the US and Canada. A recent client inquired about meeting this standard (Category 3 (ISO 13849-1/EN 954-1) I am having a difficult time finding more information on this specific requirement.

Any information is greatly appreciated.

Bouchard, James

Talk to the safety relay manufacturers, ( Pilz, Siemens, Allen Bradley-Guardmaster etc ) they all have catalogues/brochures and even training sessions on this. Of course their documentation uses examples based on their products.

The requirements are found in the ISO standard. It is the application that can be difficult to develop at a reasonable cost.

James Bouchard
Category 3 implies that a single fault in the safety system does not lead to the loss of the safety function. Therefore, redundant contacts on E-stop and safety interlocks, two contactors and a safety relay are required. Some but not all faults will be detected. See the following link for more info:
Deciding which category a safety device needs to adhere to is based on doing a risk assessment.

some risks may require a SIL 3 Cat 3 device, others you may decide to use Sil 3 Cat 3

determine what risks exists and then you can use a chart that has been developed.

The previous response is correct in typically this requires use of redundant monitored contact devices.