How Many Amps Does a Well Pump Use? (Explained)

If you’re in the same category as the 23 million people in the United States who own a well, you know how indispensable a reliable well pump can be. This handy device ensures a constant water supply, so you don’t have to worry when your local water authority is on strike, or there’s a drought. But have you ever wondered how many amps a well pump uses?

In this blog, we’ll discuss everything you need to know about the amperage requirements of pumps. We’ll look at the amperage draw for pumps with different horsepower (HP) ratings, so you can decide when shopping for a new pump or choosing the wire size for your configuration. Let’s get right into it!

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How Many Amps Does a Well Pump Use?

The amperage requirements of a well pump will vary depending on the unit’s horsepower and voltage. But generally, pumps with a higher HP will require more amps than those with a lower HP, assuming all other factors remain constant.

Before I proceed, 1 HP is equivalent to 746 watts of power. And assuming you know the voltage, it may seem easy to find the amperage draw of your unit. After all, ohm’s law states that I=V/R.

However, this isn’t always the case, especially when it comes to motor-powered units. You see, the HP rating on the appliance denotes the output power. So, there’s no way you can use that wattage rating to find the amperage draw.

Instead, you’ll need to factor in the efficiency of the unit. The goal here is to find how many watts the unit needs as the input for it to deliver the output of 746 watts. And to do that, you need to divide the output wattage by the pump’s efficiency.

Throughout our examples, we’ll use the efficiency rating of 90% or 0.9, but check your unit’s documentation to be sure. With that said, let’s move on to some numbers!

But just before that, once you have the input wattage, you still need to factor in the power factor of the machine. The power factor is the ratio between the real power that the device uses to generate its output and the apparent power. It’s a good idea to assume a power factor of 85% (0.85) for most well pumps.

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Now that we know all that, let’s get into some numbers and see how many amps a pump with different HP ratings would use.

How Many Watts Does a 1/2 HP Well Pump Draw?

A 1/2HP well pump draw will draw approximately 4.06 amps at 120V and 4.43 amps on a 110V circuit. At 240 volts, the amperage draw is lowest at about 1.55 amps. That’s relatively low, but it’s nothing to scoff at.

I know you’re probably wondering how we arrived at those numbers. Well, let’s simple with these simple steps;

Step 1: Convert ½ HP to watts

1HP = 746 Watts

½ HP = ?

=373 Watts (output wattage)

Step 2: Factor in efficiency (90% in our case)

Input wattage = (373/0.9)

= 414.44 watts

Step 3: Multiply the voltage (120) by the power factor (PF) of 0.85

= 120 x 0.85

= 102 volts

Step 4: Divide the input wattage (414.44) by the result of step 3 (102);

= 414.44/102

= 4.06 amps

These numbers will change depending on the voltage your pump is running on. If you have a 110V circuit, the amp draw will be higher because the voltage is lower.

If you find the above calculations to be confusing, don’t worry. Here’s an alternative method

Amps = HPs x 746/ (voltage x power factor x efficiency)

= 373/ (120 x 0.85 x 0.9)

= 373/91.8

= 4.06 amps

As you can see, the two methods produce the same results. So, feel free to use whichever one you’re more comfortable with.

Now, let’s see how the amperage draw changes when we increase the HP rating of our well pump.

motor-of-a-well-pump

How Many Amps Does a 3/4 HP Well Pump Use?

A 3/4 HP well pump uses approximately 6.09 amps on a 120-volt system and 6.64 amps connected to a 110-volt circuit. If you go for the higher voltage, 240 volts, the number of amps won’t be as high. In this case, it will only be 3.05 amps.

Let’s follow the same steps as before to see how we arrived at those numbers. But here, we’ll use the alternative method this time.

Amps = HPs x 746/ (voltage x power factor x efficiency)

= 559.5/ (120 x 0.85 x 0.9)

= 6.09 amps

As you can see, the amperage draw is slightly higher than that of a 1/2 HP well pump. That’s to be expected, though, because the HP rating is higher.

Now, let’s see how much current a 1 HP pump will draw.

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How Many Amps Does a 1 HP Well Pump Use?

An average size pump rated 1HP will use approximately 8.13 amps on a 120-volt system and 8.87 amps connected to a 110-volt circuit. And like before, the amperage draw is lower at 240 volts with just 4.06 amps.

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Here’s how we’ve arrived at those numbers;

Amps = HPs x 746/ (voltage x power factor x efficiency)

= 746/ (120 x 0.85 x 0.9)

= 8.13 amps

Of course, keep in mind that this amperage assumes that you’re using a 120-volt system, that your pump has a 90% efficiency rating, and that the power factor is 85%. If either of those things is different, the amperage draw will also differ.

How Many Amps Does a 1.5 HP Well Pump Use?

A 1.5 HP well pump uses approximately 12.19 amps using a 120-volt system and 13.3 amps on a 110-volt circuit. As usual, the amperage draw is lower when the voltage is higher at 240 volts with just 6.09 amps.

Here’s the breakdown of those numbers;

Amps = HPs x 746/ (voltage x power factor x efficiency)

= 1119/ (120 x 0.85 x 0.9)

= 12.19 amps

How Many Amps Does a 2 HP Well Pump Use?

As for a 2 HP well pump, it will use about 16.25 amps when running on a 120-volt system and 17.73 amps when connected to a 110-volt circuit. The amperage draw is obviously lower when the voltage is increased to 240 volts at just 8.13.

Here’s the work behind those numbers;

Amps = HPs x 746/ (voltage x power factor x efficiency)

= 1492/ (120 x 0.85 x 0.9)

= 16.25 amps

So, it depends on the HP rating of your pump as to how many amps it will use. The higher the HP, the higher the amount of power your water pump needs. But again, remember to factor in the efficiency and power factor ratings, as they will also affect the amperage draw.

What Size Breaker Should a Well Pump Be on?

An average size pump will work with 20 or 30 amps, but some may require a larger amp breaker. To be safe, always check with the manufacturer’s specifications to see what size breaker is recommended for your model. Sometimes, a pump may require a 40 amp or larger circuit breaker.

Following what the manufacturer recommends on the manual when choosing the breaker size for a well pump is ideal. The manufacturer considers the voltage drop, distance, NEC code recommendations, and more to determine the best number. 

Why Does My Well Pump Keep Tripping the Breaker?

A well pump may trip the breaker for a few reasons. It could be due to overloading, short-circuiting, issues with the pump motor, pests, or even a clogged impeller. Always check with a professional to identify the root cause of the problem before trying to fix it yourself.

Overloading

The most common reason a pump trips the breaker is that it’s trying to draw more amps than the breaker can support. This usually happens when the well pump is getting old and isn’t as efficient as it used to be. To determine whether this could be the cause, you’ll need a well pump technician to examine your appliance. 

Short Circuit

Sometimes water can leak into the pump, causing a short circuit. This can happen if there’s a crack in the casing, faulty wiring, or if the seal around the shaft is worn out. If you suspect that your appliance has a short circuit, it’s best to get it checked out by a professional.

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Pests

Pests can cause problems for your well pump, including tripping the breaker. Mice and other small rodents are known to chew through wires, which can lead to a short circuit.

If you suspect this to be the case, try setting up a trap.

Clogged Impeller

A clogged impeller can also cause your well pump to trip the breaker. The impeller is responsible for moving water through the pump, so if it gets clogged, the pump has to work harder to move the water. This can cause it to overload the breaker.

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Is It OK To Run a Well Pump 24 Hours?

Yes, running a well pump for 24 hours is OK, but that will depend on the type of motor you’re using. A high-quality starter kit sump pump can run for 24 hours, but most of them shouldn’t run for more than 2 hours.

Even with the most hardworking and durable water pump, it’s still important to give it time to cool down. Running it too long can cause the pump’s motor to overheat and eventually fail. So, take breaks in between to prolong the life of your pump.

Frequently Asked Questions

Can I Plug My Well Pump Into a Generator?

Yes, plugging a well pump into a generator is a great way to ensure that your pump will continue to run in the event of a power outage. However, you need to be sure that the generator is powerful enough to run the pump. A 3-4 kilowatt (kW) generator should be sufficient for most pumps with a ½-2HP motor.

Can You Run a Well Pump With a 2000 Watt Generator?

Yes, you can run a well pump with a 2000-watt generator, but it is important to note that only smaller generators should be used for this purpose. Ideally, a 2000-watt generator should only be used for well pumps with a 3/4HP motor or less.

Are Well Pumps 120 Or 240?

The voltage of a well pump can vary, but most pumps are available in 120 and or 240-volt configurations. But 120-volt pumps are more common in smaller HP models, while 240-volt pumps are more common in larger models.

Final Verdict

The amperage of a well pump is an essential factor to consider when sizing the breaker, choosing the ideal generator, or even when you want to gauge pump’s power usage. And while the amp draw of this piece isn’t indicated; you can easily calculate it by using the provided information about the pump. Just follow the simple formula provided, and it will give you the amperage of your pump.

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About Rinkesh

A true environmentalist by heart ❤️. Founded Conserve Energy Future with the sole motto of providing helpful information related to our rapidly depleting environment. Unless you strongly believe in Elon Musk‘s idea of making Mars as another habitable planet, do remember that there really is no 'Planet B' in this whole universe.