8 components coveredField manual · Sump / Well Pump
Submersible well pumps, 2-wire vs 3-wire and control boxes: field service manual
Covers: Single-phase 4 in submersible well pumps on a pressure switch and captive-air tank: 2-wire motors (start parts inside the motor, up to 1.5 HP) and 3-wire motors with an above-ground control box (e.g. Franklin QD 1/3-1 HP, CRC, Standard and Deluxe boxes). Constant-pressure drives are covered in their own manual.
Knowing whether the motor is 2-wire or 3-wire decides the whole diagnosis. A 3-wire system has a control box near the tank holding the start capacitor, start relay and, on larger boxes, overloads; those parts can be tested and replaced at the surface. A 2-wire motor has no box, so any start-circuit failure means pulling the pump, which is a licensed well contractor's job.
Safety first
- 240 V with high available current: lock out the breaker and verify dead before opening the box or switch
- Capacitors store charge: discharge before touching
- Live voltage and amp tests are caution work: insulated probes, dry footing, one hand
- Pulling a submersible or working on the well cap/drop pipe is for a licensed well contractor
How it works
Power runs from a double-pole 240 V breaker to the pressure switch. On a 2-wire system the switch feeds the motor directly through two conductors plus ground. On a 3-wire system the switch feeds L1/L2 in the control box, which sends power down three conductors: yellow (common), black (main/run winding) and red (start winding), plus ground.
At start, the box connects the start capacitor in series with the start winding to give starting torque. The relay (a potential-type or Franklin's solid-state QD relay) disconnects the start circuit once the motor is up to speed. CRC boxes add a run capacitor that stays in circuit for smoother running.
Larger Standard and Deluxe boxes (1 HP and up) add overload protectors with external reset buttons and, in Deluxe boxes, a magnetic contactor. Franklin QD boxes disconnect the internal components when the lid is removed, which simplifies safe testing.
The motor's own data (winding resistance by HP and cable length) comes from the motor maker's application manual (Franklin AIM). Downhole tests and pump pulling belong to a licensed well contractor.
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Always confirm values against the tech sheet for the exact model.
OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work. © 2026 OnCall Tech. Original content; not a reproduction of any manufacturer document.Generic part photos (not of this brand): Vertical pressure tank connected to a water pump outdoors by W.carter, CC BY-SA 4.0
