Grundfos MS402 and MS4000 4 in Submersible Motor

Grundfos 4 in submersible motors for 4 in and larger wells, 34 builds from 1/2 to 10 HP. The MS402 (1/2 to 2 HP, 900 lb thrust) is Grundfos’s motor for the domestic groundwater market, in single-phase 2-wire, single-phase 3-wire and three-phase builds. The MS4000 (2 to 10 HP, 1,500 lb thrust) is built for water supply duty in single-phase 3-wire and three-phase builds. All external surfaces in contact with water are AISI 304 stainless steel.

• Hermetically enclosed stator in stainless steel: no short-circuit from condensation in the windings
• MS402 insulated to reduce the risk of burnout from a lightning strike; lip seal approved for drinking water
• MS4000 ceramic/carbon shaft seal for sealing and wear life
• Cooling chambers top and bottom with internal circulation of motor liquid; factory-filled with SML-3 liquid, frost-proof to -4°F (-20°C)
• 7-1/2 and 10 HP MS4000 motors carry the Tempcon temperature transmitter, readable through an MP 204 motor protector

Sources: Grundfos US price list, effective January 1, 2026 (thrust, horsepower); Grundfos SP data booklet, 60 Hz (cooling and temperature table, materials); Grundfos Product Center (dimensions, service factor, seal, insulation, pressure, approvals).

Single-phase 3-wire builds only. Two-wire and three-phase builds do not use these boxes. The Deluxe box adds a magnetic starter to the Standard box.

Grundfos US price list, p. 48. The 1/2, 3/4 and 1 HP boxes are sold in multiples of 10. All are on our Grundfos SA-SPM6 3-Wire Control Box listing.

• Check the motor liquid level before installation and top up with tap water; use Grundfos liquid where frost protection is needed. The filling hole is on the bottom of the MS402 and on the side near the top of the MS4000.
• Set the pump at least 3 ft below the maximum drawdown level, never with the motor bottom below the top of the well screen or within 5 ft of the well bottom.
• In a lake, pond, tank or wide well, make sure the water velocity past the motor meets the cooling minimum.
• Install a voltage-rated surge arrester on the supply side of the control box or starter, grounded per the NEC.
• Check the nameplate voltage, phase and frequency against the supply, and measure insulation resistance of the cable and splice before startup.

From the Grundfos SP/SPE installation and operating instructions.

Domestic groundwater supply (MS402); water supply from 4 in wells and, with options such as an oversized motor, heavy-duty industrial and dewatering duty (MS4000).