Introduction

When ordering a submersible jockey pump for your fire protection system, you will quickly run into a choice between a 2-wire and a 3-wire motor. If you are new to the terminology, the first thing to know is that we do not count the ground wire when naming these configurations. A 2-wire pump actually contains three wires (two black, one green), while a 3-wire pump contains four (black, red, yellow, and green). The main difference between the two configurations isn’t just the wiring—it comes down to where the starting components for the motor are located.

The 3-Wire Submersible Pump

In a 3-wire system, the starting components—which include starting capacitors, running capacitors, relays, and thermal overloads—are housed externally in a separate, wall-mounted control box above ground.

Pros:

• Easy Maintenance: Because the control box is above ground, the components are easily accessible for cheap repairs.

• Superior Starting Torque: Capacitor-start systems provide more torque for severe circumstances, like deep wells or excessive static head.

• Efficient Running: Running capacitors ensure smoother operation, lower current, and lower running temperatures.

• Lighter Cable: While it requires an extra lead, the cable gauge can often be lighter.

Cons:

• Higher Failure Potential: External capacitors and non-sealed relays are susceptible to wear and atmospheric oxidation.

• Complex Wiring: The additional supply lead increases the weight and expense of the cabling.

• Power Consumption: Starting current may be higher depending on the distance of the control box from the well.

The 2-Wire Submersible Pump

A 2-wire pump builds all starting elements directly into the hermetically sealed stator housing of the motor, eliminating the need for an external control box.

Pros:

• Simplicity: Installation is faster and more straightforward with fewer components to wire and mount.

• Reliability: Internal starting switches and components are sealed from oxygen, preventing oxidation and reducing starting relay failures.

• Soft Starting: These motors typically start softer, decreasing shock loading on pump components and offering pulsed torque to clear obstructions like sand.

• Economical Cabling: The cable is simpler, lighter, and more cost-effective to purchase.

Cons:

• Difficult Repairs: If an internal component fails, the entire motor must be pulled and replaced.

• Torque Limits: These systems offer lower starting torque under severe static head compared to 3-wire counterparts.

The 1.5 Horsepower Rule

Power requirements often dictate your choice. If your application requires a motor that is greater than 1.5 HP, you must use a 3-wire configuration. The heavier motor requires the starting power provided by an external control box. For applications below 1.5 HP, 2-wire is typically recommended due to its simplicity and cost advantages.

Making Your Choice

At the end of the day, your specific circumstances will dictate the best configuration. If you prioritize a simple installation and are using a smaller motor, a 2-wire setup is excellent. If you prefer accessible, cheap repairs or need a heavy-duty motor, the 3-wire setup is the way to go.

Technical Notes

Wiring & Installation:

• 3-Wire Colors: Standard control boxes are coded Yellow, Red, Black, and Green. Any color wire can be used if order is maintained at the pigtails.

• 2-Wire 240v: Two wires (typically both black) can be connected to pigtails in any order.

• 2-Wire 120v: Wires are typically black, white, and bare.

• Resistance Tolerance: 2-wire systems require closer tolerance for resistance measurements during installation.