Choosing the Right Submersible Pump Part 2
In our previous blog we discussed the parameters of how to select the correct pump for your well based on pressure, flow and maximizing efficiency. In this blog, we are going to dive in a bit deeper and help answer questions about some of the additional details and decisions that go into installing an affordable well pump that will last for many years to come!
3 Phase or Single Phase motor?
The “pump” that many people refer to in their well is actually comprised of two specific components that are coupled together: The “pump end”, which spins and causes the water to move and the motor which takes electrical power and converts it to the rotational mechanical power the pump needs in order to spin. In our previous blog we selected a 3 HP 15 GPM FPS pump as the correct pump for pressure, flow and best efficiency in the example. So we know we need a 3 HP motor, but did you know that there are multiple motors to choose from? 3 HP 230 volt single phase, 3 HP 230 volt 3 Phase and 3 HP 480 volt 3 phase. Which one is best???
So what’s are the differences and why would you want to choose one type of motor over another? The price difference between a single and 3 phase motor is typically insignificant. Three phase motors tend be a touch more efficient and can use smaller wire size for the same horsepower motor. To understand this better and make an informed choice, we’ll first look at the maximum distance that #12 (double jacketed, stranded) Submersible Pump Wire is appropriate for with various 3 HP motors. (Refer to pages 11,19 & 20 AIM Manual)
-3 HP 230 Volt single phase: 190’ between the main incoming power panel and the submersible pump
-3 HP 230 Volt three phase: 390’ between the main incoming power panel and the submersible pump
-3 HP 480 Volt three phase: 1600’ between the main incoming power panel and the submersible pump.
See the trend? That higher the voltage/ # of phases, the longer the allowable distance for a given size of wire! Let’s look at this another way and use the 3 HP pump from part 1 of this blog that is installed almost 400’ deep in a well. That well is located 150’ from the main power meter panel that supplies electricity to the property. So we have to run power a total of 650’ from the main power panel to the well and then down to the pump. What size wire would we need to power these 3 different 3 HP motors in this application?
-3 HP 230 Volt single phase: #6 AWG submersible pump wire (4.12mm diameter)
-3 HP 230 Volt three phase: #8 AWG submersible pump wire (3.26mm diameter)
-3 HP 480 Volt three phase: #14 AWG submersible pump wire (1.63mm diameter)
Yes, American Wire Gauge is confusing as bigger wire has smaller numbers. Because copper is relatively expensive, the motor we choose is going to have an impact on our pocketbook. Based on the current, rapidly increasing cost of quality copper submersible pump cable (wire), here are some estimates on cost based on full list price with no discounts. Choosing a 230 volt single phase 3 HP motor means spending $4900 on just the wire, selecting the 3 HP 230 volt 3 phase motor will mean spending about $3100 on wire, while selecting a 3ph 480 volt motor will mean spending ~$1300 on quality wire! Please don’t try to save a few $ by using twisted solid wire in your well. It is not very flexible, often does not include the NEC ground conductor and its single layer of insulation can easily be cut or damaged by abrasion.
You can certainly see why agriculture, industry, and informed customers prefer high voltage 3 phase since it allows them to save big on long wire runs by using much smaller wire. Larger wire in your well isn’t of any use/benefit unless it is actually needed/required, so why doesn’t everyone use a 3 phase, 480 volt power supply for their wells and save lots of money on wire? Most residential homes have a single phase 230 volt power supply, that’s why! For many years, most homeowners have been stuck with 230 Volt single phase motors and the huge wire it takes to run them. The trend, however, is starting to change based on some newer technologies that involve how submersible pump motors are controlled.
Single phase pump motors have typically use a pressure switch that turns the power supply off and on to the pump motor to turn the pump on and off. The pressure switch senses when the pressure is low and the large pressure tank is nearly drained and then turn the pump on. When the pressure is high and the pressure tank is refilled the pressure switch opens the circuit and turns the pump off. Three phase motors are/were controlled in a similar fashion too with a pressure switch used to turn the power on/off to the pump that filled a relatively large pressure tank.
~20 Years ago the water industry saw the influx of a new type of motor controller based on the concept of the variable frequency drive. These controllers, sometimes called “constant pressure controllers” or “drives” were quite expensive, initially, and rarely used. Today they are becoming more and more cost competitive and common these days. So what do they do, how do they work?
These controllers typically accept single or three phase, 230 volt input power and then produce 230 volt 3 phase power for the submersible pump motor. Jumping from single to 3 phase, now allows the use of smaller, less expensive wire from the controller to the well and down the well! These controllers don’t just turn the power to the pump off and on, they vary the voltage and frequency of the power supplied to the motor to increase or decrease the motor speed of the pump. These controllers use a pressure transducer instead of a pressure switch. This pressure transducer senses the exact water pressure and the controller uses this information to speed up/slow the pump down to match the output of the pump to your exact water usage so large pressure tanks ($1500) are no longer needed and pressure tanks with just a few gallons of capacity ($115) are adequate for most applications. So, if you have single phase 230 power and you want to use a 3 phase motor and the smaller wire, you will need to purchase one of these controllers and they are almost always packaged with the appropriate pressure transducer. These controllers aren’t cheap, however, the savings on the wire($1800), pressure tank ($1385) and ease of installation typically more than make up for the cost of the controller (~$2000-$3000 depending on the 3 HP controller chosen). Keep in mind that smaller wire and pressure tanks weight less, take up less space, have less storage and shipping costs associated with them and are generally easier to work with/install so there will likley be some savings on the installation costs as well.
At OPS we’ve found many good drives including the Pentek Intellidrive, the Franklin Subdrive Connect, Danfoss, ABB, Goulds SPD & Aquavar series drives. Each of these controllers each have their price points and applications where they excel. While the major manufacturers have adopted standards that allow their pumps, motors and VFD controllers to be used interchangeably, some manufacturers give discounts and/or extended warranties if their pump/motor and controller are purchased as a package and used in conjunction with each other.
Phase Perfect, an American company with a great reputation for quality, has a great lineup of VFD controllers and has something available that nobody else has, voltage doubling! What is voltage doubling? Well, it means you can feed this controller 230 Volt single phase power and it will provide 480 volt 3 phase power without the need for additional, inefficient power transformers. This is great for deep well applications where the wire costs can be overwhelming. Another advantage is in certain specific applications. Let’s say you have a 5” well casing; the largest 230 volt 3 phase 4” submersible motor available is limited to 7.5 HP, HOWEVER, the largest 480 volt 3 phase motor available is 10 HP! So using a voltage doubling drive capable of running a 10 HP pump can allow access to more water, deeper!
To summarize, if you have a shallow well close to the incoming power meter and want to keep things simple; a single phase motor is a great choice. If you have long power runs and/or a deeper well and want to potentially save on your installation bill; it is time to start getting the pricing together for a system that includes a 3 phase motor and submersible pump controller. (VFD controllers do not make your pump or water system more efficient, so don’t add one of these devices thinking that you’ll use less electricity. There are some claims out there about this and we tested them and didn’t find any power savings.)
Galvanized Metal , HDPE or Sch 120 PVC Drop Pipe?
Drop pipe is the industry term used to describe the pipe that is used to lower the pump deep down into the well. The submersible pump wire is typically secured to this pipe in a way that keeps the wire tidy, untwisted & untangled. In order to know which drop pipe is best for your submersible well pump application, you really need to know how deep the pump is going to be set and how many horsepower the pump is (or its approximate weight).
Poly pipe is a semi-flexible black pipe that typically comes in coils and is suitable for wells that are relatively shallow. Shallow wells typically have smaller pumps and the weight of the pipe, pump, wire and water in the pipe is typically less than 100 pounds (40 KG) and thus the pump can be pulled and installed by hand. If using this pipe, always ensure that a safety rope with a strength of at least 500 pounds (200 KG) is used in the event of a problem with the pump or pipe. Also ensure that this pipe can handle the pressure you’ll expect it to handle! If your pump is 100’ deep and it needs to pump up a hill that is 300’ tall, this is the equivalent of 175 PSI. Installing poly pipe rated for 150 PSI is asking for ruptures and problems down in the well!
Galvanized metal pipe was the primary choice for many years because it can handle high weights, large pumps and pumps set to very great depths. This pipe comes in standard lengths 21’ long and ranges in diameter from 1/2” to over 12” in diameter. High quality galvanized pipe is expensive and is subject to corrosion and deterioration in the water/air environment that wells provide, particularly in the region of the water table as it rises and falls with pumping. With low pH water the problem is exacerbated and holes can develop in the pipe and, if left long enough, we’ve seen the pumps fall off the end of the pipe!
PVC drop pipe has been developed in the last 20 years that has very good strength, does not corrode and it has a decent price point. It is similar in form to the traditional galvanized piping but comes in lengths of 20’ long and diameters of 1”, 1.25”, 1.5” and 2”. Engineering charts (page 7 of certain-teed manual) must be strictly adhered to. If the depths/weights/pressures are exceeded, then very expensive problems that include fishing well equipment out of the bottom of the well can be expected! We always use Sch 120 with Stainless steel couplings (no plastic couplinds/couplers) and 1000 pound (400KG) safety rope attached to the pump. There are large diameter versions of this pipe for large pumps and wells too, check out this drop pipe calculator for the Certa-Lok type drop pipe.
Oakville Pump Service has trained professionals with decades of experience. Our professionals will help you select the correct submersible well pump for your residential, commercial or agricultural well in the Napa and Pope Valley areas. OPS knows pumps and pump manufacturers. Whether your water is deep, sandy, hot, or full of minerals; we can help you choose the pump best suited for your application. Our team will ensure you get the pump that will last the longest, work the most efficiently and be installed in a manner that represents the highest industry standards! Call us today at (707)944-2471
If you have additional questions you’d like our blog to address, please contact us and we will try to address them in future blogs!
