The problem is possibly open overload thermal elements, wiring to the motor, or - most likely - the motor itself. If the coil is energized, but voltage is still not present at the bottom of the motor starter and the motor is not operating, a dangerous condition could exist. If voltage is not being applied to the coil, then the problem is in the control circuit. If voltage is not present at the bottom of the motor starter, test the points where voltage is applied to the coil. If voltage is present, then test for voltage at the bottom of the starter. Once again, test across all three phases. The next points along the flow path to the motor - the “M1” contacts - are tested at the top of the motor starter. Meter reads â0VACâ when the lead is placed at the bottom of an open fuse. If voltage is present at the top of the each fuse, use a crisscross method to verify the fuses are good ( Fig. One of the most common problems is open (blown) fuses. If voltage is present, move to the right on the electrical diagram and test for voltage at the top of the fuses. Make sure all readings are within specification.įirst, test for voltage at the top of the disconnect. Remember, when testing for the presence of 3-phase voltage, always read across all phases: A-B, A-C, and B-C. 1, and use this concept to walk through a basic motor control circuit. The missing voltage concept means finding the point where voltage should be present, but for some reason it is not. When working on energized circuits, always follow OSHA and company electrical safe work practices ( Photo). However, diagnostic troubleshooting must often take place with circuits energized. It is always safest to first place a motor and control circuit into an electrically safe work condition through proper lockout/tagout procedures and then test for continuity. The objective is to find where the voltage is interrupted to the motor.
Begin troubleshooting by simply following the electrical flow path from left to right as the current flows toward the motor. If there are no obvious indications as to why the motor does not operate, it’s time to use your multimeter and look for the “missing voltage” in the main power circuit. Knowing your system and control circuit is critical to ensure the motor will not automatically restart when resetting overloads. If the distinctive “click” is felt as the motor starter overload reset push button is depressed, then the cause of the overload must be determined. Mechanical issues such as broken couplings can be quickly spotted. Any signs of motor overheating, such as the smell of burnt insulation, might indicate a motor ground fault and internal damage.
In this example, When beginning the investigation, look for the obvious. 1 is a schematic diagram of the typical motor and its associated basic controls. While there are just about as many variations in circuit configurations as there are types of control equipment, Fig. Because it is not always possible to de-energize when troubleshooting, always follow safe work practices and wear appropriate personal protective equipment. Tracing voltage through the main power circuit exposes the worker to potentially hazardous voltages.
SIMUTECH TROUBLESHOOTING CONTROL CIRCUITS DOOR CIRCUIT HOW TO
In Part 2, we’ll address reading basic to more complex control circuit diagrams and show you how to develop a logical and systematic approach to troubleshooting control circuits. This can help to isolate the problem to the power supply, the control circuit, or the motor itself. This article will help you understand how to trace voltage through the main power supply circuit. Typical motor circuits are divided into two main parts: the main power circuit and the control circuit. For example, if you interpret the control circuit as telling you contacts “CR105-3” should be closed, then you need to have the skills to find the CR105 relay and measure voltage across the number “3” set of contacts and determine if they are open or closed. The key to developing a logical and systematic approach to troubleshooting motors and controls is to first understand the overall concept of the motor and its associated control circuit - and then use the skills and techniques necessary to read through the control circuit diagrams and compare expectations to what is actually happening at the components. “Maybe it’s the limit switch again” or “Probably another ground fault on the motor” is not the way to minimize troubleshooting time and increase uptime on equipment.
“Easter egging” just doesn’t work unless you happen to be very lucky! When you get the call, “The motor won’t start,” you’d best have a logical and systematic plan in place to approach the problem.