Use extreme caution when working with electricity. Ensure all power has been removed from motor circuit and that the breaker has been tagged. When a bad motor winding cannot be found by a physical inspection, many times an ohmmeter may show that there is a defective winding.

how to check motor winding with multimeter pdf

Most repair shops will use a "megger" or a ground insulation tester. The megger will help to detect areas of deteriorating insulation where the windings may soon short.

Most individuals do not own a megger, but probably do have an ohmmeter. While the ohmmeter may not show potential failures, it can be used to determine if the windings are good or bad. Remove all power from the motor and isolate the circuit. Tag the circuit breaker to prevent accidental restoration of power. Open motor housing to access windings. Clean the windings and motor interior with shop air and inspect for any damage. Check winding insulation for cracks or brittleness. Connect the probes to the ohmmeter and set the meter to a midrange setting.

Touch the two leads together and make sure that the meter indicates continuity, or zero ohms. Consult the motor schematic or a diagram of the motor's windings and use the meter to measure the resistance of the windings.

Each winding leg should have some small resistance reading. The meter should not show an "open" or a "short" when a winding leg is measured. Use the schematic and take readings of all of the windings. Write down each measurement and make comparisons when measurements are complete. Daniel Ray has been writing for over 15 years. He has been published in "Florida Sportsman" magazine. He attended the University of South Florida. Hunker may earn compensation through affiliate links in this story.

Things You'll Need Volt ohmmeter with probes Common hand tools. Tip Use the link listed below in the Resources section for a Website on how to use an ohmmeter. Warning Use extreme caution when working with electricity. Test Electric Motor Windings.

how to check motor winding with multimeter pdf

Step 1 Remove all power from the motor and isolate the circuit. Step 2 Clean the windings and motor interior with shop air and 2c free music download for any damage. Step 3 Connect the probes to the ohmmeter and set the meter to a midrange setting.

Step 4 Consult the motor schematic or a diagram of the motor's windings and use the meter to measure the resistance of the windings. Step 5 Use the schematic and take readings of all of the windings. How to use an ohmmeter. Share this article. Daniel Ray. Show Comments.The rotor of a squirrel-cage motor. This is why we call this type of connection "Star" or Y. A star connection is accomplished simply by bridging one horizontal row in the connection box. This is a photo from the connection box of a motor connected in Star.

A Delta connection is easily accomplished by bridging the 3 columns in the connection box vertically. This is a photo from the connection box of a motor connected in Delta. Continue reading. But if you have questions please use the forum instead to post it. Thank you. Today my all doubts are clear abt motor connection. Very helpful. Really good. Thanks At 2 Novemberuser M. My husband cut the wires and took some resistance readings. It has 4 wires. There was no reading between any of the wires and the green one which he assumes is the ground.

Do these reading point to a problem with the motor. Just a great piece of technical writing! At 18 Novemberuser Michael L. Rappaport] Beautifully written and illustrated article. It would be good if material could be added about the result of not having one phase in both the Y and delta configurations. White] Do you have same information for 12 lead 3 phase motor? I found out my windis are not da same while doing continuity test with my meter.

Now I had to balance the windings, I had I could not calculate my percentage difference becouse onfinity is too big it has mo value. My qiestion what was I surpose to do??

how to check motor winding with multimeter pdf

Whts infinity value?? Concise and easy to understand, although not what I was looking for. How can i find the high and low speed windings.??

C:F part number The machine is indicating Error motor too hot after running for 4minutes. The winding resistance is 1.When an electric motor fails to start, runs intermittently, runs hot, or continually trips its overcurrent device, there my be a variety of causes.

how to check motor winding with multimeter pdf

Sometimes the trouble lies within the power supply, including branch circuit conductors or motor controller. Another possibility is that the driven load is jammed, binding or mismatched.

If the motor itself has developed a fault, the fault may be a burnt wire or connection, a winding failure including insulation deterioration, or a deteriorating bearing. A number of diagnostic tools — a clamp-on ammeter, temperature sensor, Megger, or oscilloscope — may help illuminate the problem. Preliminary often definitive tests generally take place using the ubiquitous multimeter.

This tester is capable of providing diagnostic information for all sorts of motors. If the motor is completely unresponsive, no ac humming or false starts, take a reading at the motor terminals. If there is no voltage or reduced voltage, work back upstream. Take readings at accessible points including disconnect sthe motor controller, any fuses or junction boxes, and so on, back to the over-current device output at the entrance panel.

What you are looking for is essentially the same voltage level as measured at the entrance panel main breaker. When there is no electrical load, the same voltage should appear at both ends of the branch circuit conductors. In a three-phase hookup, all legs should have substantially equal voltage readings, with no dropped phase. If these readings vary by a few volts, it may be possible to equalize them by rolling the connections, taking care not to reverse rotation.

The idea is to match supply voltages and load impedances so as to balance the three legs. If the electrical supply is satisfactory, examine the motor itself. If possible, disengage the load. This may restore motor operation.

With power disconnected and locked out, attempt to turn the motor by hand. In all but the largest motors the shaft should turn freely. If not, there is an obstruction inside or a seized bearing. Fairly new bearings are prone to seizure because the tolerances are tighter. This is especially true if there is ambient moisture or the motor has been unused for a while.

Often good operation can be restored by oiling front and rear bearings without disassembling the motor. If the shaft turns freely, set the multimeter to its ohms function.

The windings all three in a three-phase motor should read low but not zero ohms. The smaller the motor, the higher this reading will be, but it should not be open. For proper motor operation, all windings must have megohm readings to ground, i. If a winding is grounded out, the winding insulation is broken down or the armature is touching the stator, unless there is a possibility of a loose or chafing wire inside. Small universal motors, as for portable electric drills, may contain extensive circuitry including a switch and brushes.

In the ohmmeter mode, connect the meter to the plug and monitor the resistance as you wiggle the cord where it enters the enclosure. Move the switch from side to side and, with a trigger switch taped so it remains on, press on the brushes and turn the commutator by hand. Any fluctuation in the digital readout may point to a defect. Often a new set of brushes is what is needed to restore operation. Amperage readings are useful in all kinds of electronic and electrical work.During these challenging times, we guarantee we will work tirelessly to support you.

We will continue to give you accurate and timely information throughout the crisis, and we will deliver on our mission — to help everyone in the world learn how to do anything — no matter what.

Thank you to our community and to all of our readers who are working to aid others in this time of crisis, and to all of those who are making personal sacrifices for the good of their communities. We will get through this together. Updated: March 29, References. When a motor fails, it is often difficult to see why it failed just by looking at it.

A motor placed in storage may or may not work, regardless of its physical appearance. A quick check-out can be done with a simple ohm meter, but there's a lot more information to collect and weigh before actually putting it to use. At no time during the motor check out is power required. If it is connected - disconnect it before attempting the steps below. To check an electric motor to see why it failed, look at the outside for signs of debris that has been sucked into the motor windings, as well as broken mounting holes or feet, and darkened paint that could indicate excessive heat.

Turn the rotors and push and pull the shaft to test the bearings; if the rotors move smoothly and there is little to no movement in the shaft, the bearings are probably fine. If the problem seems to be electrical, use an ohmmeter to check resistance value.

For information on how to check the fan and the bell housing, read on!

The basics of motor testing

Did this summary help you? Yes No. Log in Facebook Loading Google Loading Civic Loading No account yet? Create an account. We use cookies to make wikiHow great. By using our site, you agree to our cookie policy.Knowledge of the basics together with powerful new test equipment vastly simplifies the job. Electric motors have had a reputation for being a mix of science and magic. So when a motor fails to operate it may not be obvious what the problem is.

Knowing some basic methods and techniques along with having a few test instruments handy helps detect and diagnose problems with ease. When an electric motor fails to start, runs intermittently or hot, or continually trips its overcurrent device, there my be a variety of causes. Sometimes the trouble lies within the power supply, including branch circuit conductors or a motor controller.

Another possibility is that the driven load is jammed, binding or mismatched. If the motor itself has developed a fault, the fault may be a burnt wire or connection, a winding failure including insulation deterioration, or a deteriorating bearing. A number of diagnostic tools, such as clamp-on ammeters, temperature sensors, a Megger or oscilloscope, can help illuminate the problem. Preliminary tests generally are done using the ubiquitous multimeter.

Basic Winding Resistance Test

This tester is capable of providing diagnostic information for all kinds of motors. Electrical measurements If the motor is completely unresponsive, no ac humming or false starts, take a voltage reading at the motor terminals.

If there is no voltage or reduced voltage, work back upstream. Take readings at accessible points including disconnects, the motor controller, any fuses or junction boxes, and so on, back to the over-current device output at the entrance panel. When there is no electrical load, the same voltage should appear at both ends of the branch circuit conductors.

In a three-phase hookup, all legs should have substantially equal voltage readings, with no dropped phase. If these readings vary by a few volts, it may be possible to equalize them by rolling the connections, taking care not to reverse rotation. The idea is to match supply voltages and load impedances so as to balance the three legs. If the electrical supply checks out, examine the motor itself. If possible, disengage the load.

This may restore motor operation. With power disconnected and locked out, attempt to turn the motor by hand. In all but the largest motors the shaft should turn freely. If not, there is an obstruction inside or a seized bearing. Fairly new bearings are prone to seizure because the tolerances are tighter. This is especially true if there is ambient moisture or the motor has been unused for a while.

Often good operation can be restored by oiling front and rear bearings without disassembling the motor. If the shaft turns freely, set the multimeter to its ohms function to check resistance. The windings all three in a three-phase motor should read low but not zero ohms. The smaller the motor, the higher this reading will be, but it should not be open. A wide range of DMMs are available to measure voltage, current, and resistance, depending on the motor power ratings.

Small universal motors, such as those used in portable electric drills, can contain extensive circuitry including a switch and brushes. In the ohmmeter mode, connect the meter to the plug and monitor the resistance as you wiggle the cord where it enters the enclosure. Move the switch from side to side and, with a trigger switch taped so it remains on, press on the brushes and turn the commutator by hand.

Any fluctuation in the digital readout may point to a defect. Amperage or current readings are useful in motor testing as well. Multimeters always have a current function, but there are two problems with it. One is that the circuit under investigation must be cut open and later restored to put the instrument in series with the load. The other difficulty is that the typical multimeter is not capable of handling the amount of current present in even a small motor.

Basic motor testing with multimeters and ammeters

All the current would have to flow through the meter, burning the probe leads if not destroying the entire instrument.A motor fails when its windings short to ground, short to each other, or open--a break in the winding's wire. The wire in the windings use an insulating covering as an isolation barrier. If the winding's insulation wears away near the motor's case, the bare-wire winding shorts to ground.

Technicians should perform a series of tests on an electric motor during routine preventive maintenance or before replacing it; this includes testing the motor for grounded windings.

Disconnect the electricity to the motor. If the motor's appliance plugs into a wall receptacle, then remove the plug from the receptacle. If the motor operates an appliance that connects to a circuit breaker, like an air-conditioning compressor-motor, then turn off the appropriate circuit breaker.

Access the motor's electrical connections and its case. Each type of motor application requires its own type of access. For example, pull the back panel off of a refrigerator to reach the condensing fan motor or disconnect a ceiling fan to reach its motor. Label each motor wire with a masking tape tag and a pencil. Make notes on the tape identifying the wire's terminal. In most cases, wire terminals have identification labels stamped next to the terminal.

Disconnect all motor wires. If the motor wires use slide-on terminal connectors, then grasp the terminal connector with needle-nose pliers and pull it off the wire terminal. If the motor uses screws to hold the terminal connectors in place, then loosen the screw with the correct screwdriver, often a Philips-head, and remove the terminal connector.

Turn a multimeter or ohmmeter to its highest resistance setting. A multimeter has voltage, amperage and resistance settings. Ohmmeters read resistance. Touch one of the meter's probes to the motor's case. If the manufacturer painted the motor's case, then scrape the paint from a small area with a screwdriver and then place the meter probe on the bare spot. Touch the meter's second probe to one of the motor's wire terminals.

Read the meter. The meter should read infinite. If not, then the motor's windings are shorted to ground. Repeat this step for each wire terminal. Based out of Central Florida, Robert Sylvus has been writing how-to and outdoor sports articles for various online publications since Sylvus has been a home improvement contractor since He is a certified HVAC universal technician. Hunker may earn compensation through affiliate links in this story.

Always test motors for grounded windings before replacing them.Check for burnt, damage to body or cooling fan or shaft. Look out for smooth and free shaft rotation.

If shaft rotation is free and smooth, bearing is possibly in good condition, otherwise consider replacing, repair or carry out further diagnosis. Examine the name plate thoroughly and compare values of running amps test see below with name plate value Earth Continuity and Resistance Test With a multimetermeasure the resistance between motor frame body and earth.

A good motor should read less than 0. Any value greater 0. Check that the correct voltage is applied to the motor using a multimeter. Ensure the terminal for power supply is in good condition. Check the connection bar for terminal U, V, and W. Each phase to phase must have a continuity if winding is OK. If any particular phase fails the continuity test, your motor is probably burnt.

Please see how to identify three phase windings for proper winding identification. U, V, W is a European winding designation. The ohms reading for each winding must be the same or nearly the same. Remember that the three phases have identical windings or nearly so! Insulation Resistance Test Insulation resistance failure of an electric motor is one of the first signs that the motor is about to fail.

For a three phase motor, insulation resistance is usually measured between each motor winding or phase and between each motor phase and motor frame earth using an insulation tester or megger. Set the voltage setting of the insulation resistance tester to V.

See how to measure insulation resistance of Electric Motor Running Amps Test With the motor running, check the full load amps FLA with a suitable meter or preferably a clamp on meter and compare with the name plate FLA.

Deviations from rated FLA could signify problems with the motor under test. Labels: Electric Motors.