The Castair S102 is the OEM magnetic motor starter for 10 HP, 208/230-Volt, three-phase Castair piston air compressors. Three-phase starters are significantly more common than single-phase in shop environments above 5 HP — three-phase motors are more efficient, produce less heat, and draw lower starting current than equivalent single-phase motors. The S102 comes with overload relay and requires three B45 heater elements — one per phase — for proper three-phase overload protection.
Three-Phase vs. Single-Phase at 10 HP
If you have the choice between the S101 (single-phase) and S102 (three-phase) for a 10 HP installation, the three-phase version is preferable when three-phase power is available. Three-phase 10 HP motors run cooler, start with lower inrush current, and typically last longer than single-phase equivalents. The S102 starter reflects this — the contactor rating and heater element sizing (B45 vs. B70) are smaller because the three-phase motor draws less current per phase at the same output power.
Heater Element Specification
The S102 requires three B45 heater elements — one per phase. Each phase of a three-phase overload relay has its own heater element. If any single phase draws excessive current (due to phase loss, unbalanced voltage, or motor fault), the corresponding heater trips the overload relay and disconnects the motor. This protection is critical — phase loss on a three-phase motor causes the remaining two phases to carry the full load, rapidly overheating the motor winding.
Castair Magnetic Starter Lineup — Three-Phase 208/230V Models
- S52 — 5 HP, 208/230V, 3-phase, heater: B25 (×3)
- S72 — 7.5 HP, 208/230V, 3-phase, heater: B36 (×3)
- S102 (this unit) — 10 HP, 208/230V, 3-phase, heater: B45 (×3)
- S152 — 15 HP, 208/230V, 3-phase, heater: B70 (×3)
- S202 — 20 HP, 208/230V, 3-phase, heater: CC87.7 (×3)
For 460V three-phase applications, see the S104 (10 HP, 460V) — different contactor and heater sizing for 460V operation.
Technical Specifications
- Part Number: S102
- Motor Horsepower: 10 HP
- Voltage: 208/230 Volt
- Phase: 3-Phase
- Overload: Included
- Required Heater Elements: B45 — qty 3 (one per phase)
- Manufacturer: Cast Air
Why Buy From OEM Diagnostic Tools?
OEM Castair starters with the correct three-phase contactor and overload relay. Free shipping on qualifying orders. Free tech support at 866-217-0063. Full Castair manufacturer warranty. Let us know if you also need the three B45 heater elements — we can supply the complete starter assembly.
Call 866-217-0063 for quick answers and help!
