What Is the Difference Between A 2 Wire And 3 Wire Submersible Pump?

A submersible pump is a centrifugal pump that is used to pump water out. It is used as a sump pump and also, at times, for irrigation purposes due to its durability and efficiency. There are two types of submersible pumps – a 2-wire pump and a 3-wire pump.

The following are some of the fundamental differences between the two:

  • A 3-wire has a higher horsepower
  • For a 2-wire, components are sealed inside the motor housing, and for a 3-wire, it is in a control box
  • Starting torque of a 3-wire is 150 percent higher than a 2-wire
  • Installation of a 2-wire is easier
  • A 3-wire has a longer lifespan

In terms of function, both the 2-wire and the 3-wire are the same. They pump water out of the well or basin. However, if you want to know more about the differences in detail, then you can continue reading this article.

How do you know if your submersible pump is a 2-wire or a 3-wire?

· Appearance

Just by taking a look at them, you can instantly tell one of the primary differences between the two. You will notice that the 2-wire pump has two back wires coming out of it, and the 3-wire pump has three wires that are color-coded as black, yellow, and red.

Each of these three wires corresponds to the components inside the control box. Although, both of them have an additional ground wire that is color-coded as green. It is, however, not taken into account.

· Relay and Start Capacitor

Another difference between the two is that the relay and start capacitors are placed at different locations. When the pump needs to be activated, the pressure switch allows the electricity to flow through. The switch is usually located around the pressure tank. It then activates the relay and starts the capacitor.

In a 2-wire pump, the capacitor is located inside the pump, which is placed underwater. Whereas in addition, a 3-wire pump is not installed inside the pump. Instead, it is located in a control box that is usually placed above the well or the basin.

· Start capacitor

A 2-wire pump is more reliable and cost-effective, especially when it comes to replacing the black hot wires. However, when the start capacitor fails, you will have to replace the entire pump since that is placed inside.

On the other hand, if the start capacitor gets defective or fails in a 3-wire pump, you don’t have to replace the entire unit. Instead, you can simply replace the control box that is situated outside the well.

· Horsepower

If you want a more powerful pump, then the 3-wire submersible pump motor is the obvious choice. A single-phase 3-wire pump can go up to 15 horsepower. At the same time, a 2-wire one can only work up to 1.5 horsepower.

· Convenience in installation

Electrical components such as starting capacitors, thermal overloads, and running capacitors are built inside the pump house on the motor of a 2-wire pump. With everything fitting inside a single unit, it makes the installation process easy.

Comparatively, installing a 3-wire pump is a much lengthier process since all the electrical components are located in an above-ground control box that is mounted onto the wall.

· Oxidation

Since the starter components for a 2-wire pump are sealed inside the motor housing, they are less prone to oxidation or any type of failure.

Whereas in a 3-wire, the components are exposed to the outside environment, which means they can easily come in contact with air and moisture. These agents can easily cause oxidation and eventually cut short the lifespan of a component.

· Starting torque

If you compare the starting torque of both types, you will notice a massive difference between the two. For a 2-wire, the starting torque is less than 200 percent than the full load. And for a 3-wire, the starting torque is about 350 percent of the maximum load.

· Life span

When it comes to the average lifespan of the two, the 3-wire has a slightly longer shelf life. In general, a 2-wire pump can last for 8-14 years. And, a 3-wire pump can last for 15-19 years.

· Cost

Although the installation of a two-wire pump is much lower than that of a three-wire, the cost of the pump itself is much higher than the combined price of a three-wire pump and the control box.

Types of 2-wire pumps

  • PSC or permanent split Capacitor – In this type, the starting components never disengage from the circuit. This makes the pump more reliable. But, it reduces the efficiency of the overall operation and also reduces the lifespan as well.
  • Split phase – Sometimes, during the startup process of the pump, the starting components phase-out of the circuit, creating some issues. The pump has a specialized switch that removes any debris that can get caught in the shaft during operation. So, the switch gets activated the moment the components phase out and then attempt to get rid of the dirt.

Types of 3-wire pumps

  • CSIR or Capacitor Start Induction Run – In this type, after the startup process is over, the starting components switch out of the circuit. Once the motor reaches about 70 to 75 percent of its speed, the starting components disengage along with the winding.
  • CSCR or Capacitor Start Capacitor Run – similar to the CSIR, the starting components disengage when the motor reaches 70 percent. However, the run capacitor always remains engaged in the circuit. The advantage of having this feature is that, in the event of frequent pressure variation, the run capacitor can help in smoothing out the load transitions.

Control box

Every 3-wire pump is linked to a control box that relays the signal and operates the pump. There are primarily two types of control boxes – standard and deluxe.

The deluxe boxes have an inner lining of magnetic contractors on the door. They are appropriately synced to the rating of the motor. The standard ones have external contractors.

Every control box is equipped with different sizes of knockouts and easily grants you access to the grounding lugs.

The box is labeled on the inside, indicating each wire connection according to their color-code.

Final words

As you can see, there are many differences, advantages, and disadvantages between a 2-wire and a 3-wire submersible pump. Therefore, when you are thinking of buying a pump, you can weigh the advantages against the disadvantages and make an informed decision.

We hope this article was of help, take care!

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