What the 3PST-NO and Category 4 ratings mean for the machine guard circuit
The Omron G9SA-321-T30 is a safety relay with a 3PST-NO contact arrangement, rated for Category 4 per ISO 13849-1. That 3PST-NO means three normally-open force-guided contacts that switch together, so when you wire them in series with the machine's power contactors, any single fault in the relay itself or the guard switch circuit is detected at the next demand cycle — the redundant structure is what earns Category 4.
Listed as current production. No official successor or cross-reference on record. Sourced to order against the BOM quantity — confirm the guard circuit contact count and the mating base before committing. Pricing and availability confirmed at quote time.