Siemens 3RH21221AK60 Auxiliary Contactor Relay
3RH21221 Series Family Notes
The 3RH21221 prefix places this unit within Siemens' 3RH2 auxiliary contactor relay series, sharing the same base part number with all listed alternates. Coil consumption holds constant at 37VA across the family regardless of coil voltage variant.
Contact Form and Circuit Configuration
The seed specifies a 3PST-NO (3 Form A) contact arrangement delivered in bulk packaging with chassis/DIN rail mounting. Several alternates (AK20, AC60, AG60, AU60, AR60, AN60) specify a 4PST-2NO/2NC configuration adding two normally-closed poles, which panel builders should verify against existing wiring diagrams before substitution.
| Spec | 3RH21221AK60 (seed) | 3RH21221AK20 | 3RH21221AP60 | 3RH21221AT60 |
|---|---|---|---|---|
| Coil Voltage | 120VAC | 120VAC | 240VAC | 600VAC |
| Must Operate | 102 VAC | 102 VAC | 204 VAC | 510 VAC |
| Contact Form | 3PST-NO | 4PST-2NO/2NC | 3PST-NO | 4PST-2NO/2NC |
| Coil Power | 37VA | 37VA | 37VA | 37VA |
| Mounting | Chassis/DIN | Chassis/DIN | Chassis/DIN | Chassis/DIN |
| Operate Time | 33 ms | 33 ms | 33 ms | 33 ms |
| Encapsulation | Bulk | Box | Bulk | Box |
| Similarity | — | 1.0 | 1.0 | 1.0 |
The reader must qualify each alternate independently for their specific installation requirements; similarity scores reflect parametric overlap only.
3RH21221AK20 matches the seed coil voltage (120VAC) and maintains the same must-operate threshold of 102 VAC. The difference lies in contact arrangement—two normally-closed poles replace one normally-open pole, affecting auxiliary circuit wiring topology.
3RH21221AP60 retains the seed contact form (3PST-NO) and bulk packaging but doubles the coil voltage to 240VAC with a corresponding must-operate value of 204 VAC, useful for European mains configurations.
3RH21221AT60 targets higher coil voltage applications at 600VAC nominal with a must-operate of 510 VAC, maintaining the 37VA consumption and 33 ms operate time despite the voltage difference.
Engineering Verification Checklist
- Confirm coil voltage matches control circuit nominal (120VAC for AK60)
- Verify must-operate voltage (102 VAC) provides adequate margin with expected supply tolerance
- Confirm required contact form: 3PST-NO (seed) or 4PST-2NO/2NC (alternates)
- Verify mounting compatibility with existing DIN rail or chassis cutout
- Check enclosure temperature rating against 25°C ~ 60°C operating range
- Confirm auxiliary contact function matches PLC input or indicator circuit requirements
- Verify packaging preference: bulk (seed, AP60) versus box (alternates)
- Review coil VA burden against control transformer or power supply capacity when multiple relays are energized simultaneously