In this episode of “EC&M Tech Talk,” Randy Barnett, an electrical instructor, trainer, inspector, journeyman electrician, and safety expert, walks viewers through the basics of electromagnetic motor starters, including what they are, how to troubleshoot them, and their NEC requirements.
First, Randy begins with an overview of the two key parts of a motor starter. The top portion is called a starting contactor, which is a special- purpose relay with contacts designed to safely start an electric motor. The bottom portion is the overload relay. He explains how the two parts work together to start a motor safely.
Next, Randy takes the motor starter apart. He explains that this motor starter is a NEMA size 1 unit, which is designed to operate a 10 hp 460V motor. First, he opens the starting contactor and removes the coil of wire. When that coil is energized, the electromagnetic field pulls in the white lever, which pivots downward to the contacts. After removing the top portion, Randy shows the movable contacts, followed by the stationary contacts (top and bottom). He then pulls off the thermal overloads.
Randy also explains which parts of the motor starter can go bad and will need to be replaced, including the coil, contacts (information on replacement can be found in the NFPA 70B Standard), and overloads. What size overloads are required? Randy points viewers toward NEC Art. 430.
After taking apart the starter, Randy goes on to reveal basic troubleshooting techniques and reminds viewers of the importance of making sure circuits are de-energized before doing any troubleshooting. What are some things that users can test for? Randy demonstrates tests to check for continuity through the entire circuit and resistance on the coil.
Finally, Randy discusses the 2020 NEC requirements outlined in Art. 430 for motors, motor circuits, and motor controllers that are particularly useful to operate electromagnetic motor starters safely and effectively. Under Part VII, “Motor Controllers,” Sec. 430.81 requires users to have “suitable controllers for all motors,” which in the case of this video is an electromagnetic starter, while Sec. 430.82 has to do with controller design. Under Part IX on “Disconnecting Means,” Sec. 430.102 deals with the location of the disconnect, while Sec. 430.103 discusses operation.
Also check out Randy’s latest article, “Use It, or Lose It,” which outlines five practical tips to keep you at the top of the electrical trade. And check back for next month’s edition of “EC&M Tech Talk” in August.
Barnett is the electrical codes and safety program manager for NTT Training in Centennial, Colo.