Siemens 3RT20281AK60 Contactors
Contact Configuration and Coil Power Trade-offs
The 3RT20281AK60 provides a compact 38A three-pole contactor with a single auxiliary contact pair (1NO/1NC). Its 81VA inrush coil consumption is a panel-builder constraint: the 120VAC coil draw sits between lower-voltage variants (79VA at 110VAC) and higher-voltage units (87VA at 480VAC and above). This mid-range power draw affects:
- Control transformer sizing — 81VA holding current must multiply by the number of simultaneously energized coils in the starter circuit
- Must-operate voltage margin — 96 VAC dropout threshold leaves only 20% margin below rated coil voltage; adequate for stable 120V control circuits but leaves no headroom on sag-prone supply branches
- Auxiliary contact count — the single NO/NC pair limits feedback options (interlock, status, alarm) without adding an auxiliary block; the alternate 3RT20281AK643MA0 offers 2NO/2NC at the same current rating
- Operating temperature ceiling — 60°C maximum restricts use in enclosed panels without thermal derating; most industrial control rooms stay below this but sealed enclosures near heat sources do not
- Mechanical operate time — 40 ms is consistent across the S0 series but should be verified against fast-acting safety circuit timing requirements
Comparison Against Siemens 3RT2028 Family (Coil Voltage Variants)
All listed alternates share the same base number (3RT2028), contact rating (38 A), and mounting (chassis/DIN rail). The reader must qualify these parts independently against the specific installation.
| Spec | 3RT20281AK60 (seed) | 3RT20281AK643MA0 | 3RT20281AP60 | 3RT20281AN60 | 3RT20281AG60 |
|---|---|---|---|---|---|
| Coil Voltage | 120VAC | 120VAC | 240VAC | 220VAC | 110VAC |
| Must Operate | 96 VAC | 96 VAC | 192 VAC | 187 VAC | 93.5 VAC |
| Coil Power | 81VA | 79VA | 81VA | 79VA | 79VA |
| Contact Form | 3PST-NO | 3PST-NO | 3PST-NO | 3PST-NO | 3PST-NO |
| Auxiliary | 1NO/1NC | 2NO/2NC | 1NO/1NC | 1NO/1NC | 1NO/1NC |
| Encapsulation | Bulk | Box | Bulk | Box | Box |
| Operating Temp | 25–60°C | 25–60°C | 25–60°C | 25–60°C | 25–60°C |
- 3RT20281AK643MA0 — matches coil voltage and current exactly; the 2NO/2NC contact arrangement suits interlock-and-status circuits without auxiliary block additions; packaged as box quantity rather than bulk
- 3RT20281AP60 — 240VAC coil halves control current draw, reducing wire sizing burden in long control runs; must-operate voltage rises to 192 VAC, requiring a true 240V supply rather than a boosted 208V circuit
- 3RT20281AN60 / 3RT20281AG60 — 220VAC and 110VAC coil options serve regional supply conventions and allow tighter margin on the must-operate threshold (93.5 VAC for the 110VAC unit mirrors the 96 VAC of the 120VAC unit)
- 3RT20281AV60 / 3RT20281AU60 / 3RT20281AT60 / 3RT20281AR60 — higher coil voltages (277–600VAC) serve specialized control schemes or dual-voltage applications; power consumption climbs to 87VA and must-operate thresholds demand careful supply characterization