Guidelines for electrical installations are contained in the National Electric Code (NEC). The code contains general requirements regarding the type of cable to be used when installing pumps, but the installer is given some latitude as to the specific type of cable. The purpose of this article is to help the pump installer decide which type and size of pump cable to use.
There are two classifications of insulated multi-conductor cable used in submersible applications - submersible pump cable and underground feed cable, known commonly as UF. Submersible pump cable is used between the wellhead and the pump in submersible applications, and is approved by Underwriters Laboratories (UL) for underwater duty. It is designed to safely carry electrical loads inside water wells so long as it is sized properly. UF, on the other hand, is used between the wellhead and the pump control panel, and can be buried in the ground, local codes permitting. Some local codes require underground high voltage wiring, even UF, to be run in conduit.
Submersible Pump Cable Makeup -The components of submersible pump cable: the conductors, which are the copper wires that conduct the electricity; the insulation, which is the plastic or rubber material covering the copper conductors that keep the conductors from shorting between themselves or to ground; and, in one type of pump cable, a jacket, which is a rubber or plastic material covering the insulated conductors.
Although flat-jacketed cable provides the most mechanical protection, it is the most expensive. Use flat-jacketed for sure with steel well casing, or if you are working in a hard-rock hole where abrasion of the pump cable between the drop pipe and the inner wall of the well is likely to occur. On the other hand, if you are using PVC well casing, the twisted or flat-parallel would be a reasonable choice, mainly because of the lower cost (the two are about the same price), and the fact that the conditions in the well do not lend themselves to excessive abrasion.
Stranding -This is the term used to describe the individual copper strands that make up the conductors that make up the pump cable; the finer the stranding, the more flexible the cable. You can buy size 10 pump cable with as few as 19 strands from some manufacturers, and as many as 49 strands from others. If flexibility is important to you, for instance, if you live in a cold climate where the cold temperature makes the cable difficult to work with, consider choosing a product with finer stranding.
Grounding the Pump -In 1989, the NEC started requiring all submersible pump motors to be grounded to the service entrance. This means running a green ground wire from the motor to the service entrance. You no longer can use steel drop pipe as a grounding link, according to code. For your own sake, don't even think of installing a submersible pump without grounding it according to the code. If something were to happen to one of your customers that could remotely be traced to your doing something not up to code, you would stand to loose everything. It's not worth the risk.
Sizing Tables -The Franklin Electric Submersible Motor Application Installation & Maintenance (AIM) Manual contains cable-sizing tables. A copy of one of the tables is shown above. These tables list the maximum number of feet of each size cable you can run from the service entrance to the motor for each horsepower motor, based on a maximum 5-percent voltage drop. From Table 1, 14-gauge, 75-degree C pump cable is suitable for use with a 1-HP 230-volt motor, which is up to 250 feet from the service entrance.
Franklin's manual has tables for both 60-degree C and 75-degree C-rated pump cable, both of which are available in the marketplace. The higher temperature rating allows for smaller cable sizes in certain situations. Make sure you use the table appropriate to the cable you are buying. If you do not have a copy of this motor manual, you can view or order it online at www.franklin-electric.com/Manual/contents.html or call Franklin's hotline at 800-348-2420 and ask for a free copy.
As with most major components in a water system, you have a lot of options available in your choice of pump cable. With a little research and some forethought, you will be able to choose the right product for your particular situation.
Next month, we will continue the series on downhole components with a look submersible pump cable splicing. 'Til then….