CSIR vs. CSCR: What’s the Difference?

If you’ve heard the terms “CSIR” and “CSCR” and wondered what they mean, you’re not alone. This is a common question, and the answer may have a significant effect on how your motor runs, depending on its size and application.

 Franklin Electric manufactures 2 types of single-phase, 3-wire submersible motor systems: capacitor-start/induction-run (CSIR) and capacitor start/capacitor run (CSCR). Actually, both systems use the same induction-run motor design. The difference, however, is evident in the control box.

The control box in a capacitor-start/induction-run (CSIR) system contains a relay and a start capacitor. The start capacitor is connected to the start winding in the motor (the red lead). The motor starts using both windings, but as the motor in the CSIR system comes up to speed, the relay removes the start winding and the start capacitor from the circuit. This happens in about one-third of a second, and the motor then runs on the run winding alone with no capacitor. This is why the current in the red lead of a CSIR motor will be zero after the motor has started.

The control box in a capacitor start/capacitor run (CSCR) system has 3 components: a relay, a start capacitor, and a run capacitor. The start capacitor is black, and the run capacitor is generally gray or silver. Prior to the motor’s start, both the start and run capacitors are connected to the start winding. Once again, the motor in the CSCR system reaches operating speed in about one-third of a second. And once again, the start capacitor is removed from the circuit, just as in the CSIR motor. In this case, however, the run capacitor and the start winding remain in the circuit, and the motor runs using both windings.

The result is that motors in CSCR systems are slightly more efficient, tend to have slightly higher starting torque, and tend to run slightly smoother than motors in CSIR systems. In smaller horsepower ratings (1 hp or below), the differences are usually not enough to be significant.

In larger ratings, the advantages of the run capacitor become more significant, and all Franklin single-phase 3-wire motors 1½ Hp and above are CSCR systems. That is, their control boxes all have one or more start and run capacitors. Since the run winding remains in the circuit of a CSCR motor after starting, there will always be current in the red (start winding) lead. Values can be found on page 13 of Franklin’s Application-Installation-Maintenance (AIM) Manual, August 2000 edition.

For 1 hp and below, the standard configuration of Franklin single-phase 3-wire motor systems is CSIR. That is, there is no run capacitor in the control box. However, in some cases, there may be a need to convert these installations to a CSCR configuration. Long-running applications such as fountains and aerators are the most common examples. Since many of these installations run continuously, every percentage point of efficiency may be important.

These systems can easily be converted into a CSCR configuration using Franklin’s CRC Box, or “Capacitor Run Control” Box. The CRC Box comes in the familiar QD Box configuration, so reconfiguration becomes a simple matter of removing the standard QD lid and replacing it with the CRC lid. The CRC Box is available in 230V ratings, ½ hp, ¾ hp and 1 hp.

In case you’re wondering where Franklin 2-wire motors fit in, they too are induction-run motors, and have both a start and a run winding. However, these motors do not use capacitors, and therefore have no need for a control box. Instead, there is a switch inside the motor (the BIAC switch) that removes the start winding from the circuit on start-up, just like the 3-wire capacitor-start, induction-run motor.

The bottom line is that, although there are differences, each of these single-phase motors is more alike than different. If you want to know more about the CRC Box or have other installation questions, contact our Submersible Service Hotline. Our Headquarters Service Engineers are available by telephone at 800.348.2420, or by e-mail at hotline@fele.com. You may also visit our web site at www.franklin-electric.com to view our online AIM manual and other product and service information.