Q&A for How to Check an Electric Motor

Set a Digital Volt Ohm Meter (DVOM) to the ohm setting and test the motor while the power is shut off. On average, most motors will have little resistance.

You can find that by checking the ohms between the motor terminals, if shorted or not .

Check that the brush springs still have enough tension to hold them securely to the commutator. If not, they could be skipping across high spots on the commutator.

Get out your ohmmeter, open up the fan, and check the continuity of all of the coils in the fan motor. One of them is probably open.

Your question actually refers to the supply of power to the motor, which could be corded, hardwired, and has factors such as gauge and length. However, if you are actually asking, "How do I connect the wires in a motor?", not all motors are the same. It depends on the voltage supply, such as 110v or 220v. The best answer I can give is to follow the instructions supplied with the motor. It should provide voltage tables matching the correct color codes and / or jumper settings for voltage selection.

If it's a single-phase type, you just need to move L1 (the only phase) between the 02 leads of the capacitor. If it's a 3-phase motor, you have to swap only two phases.

My table saw motor has an inconspicuous built in circuit breaker button that tripped on low voltage/high load. It took me a long time to find it. Look for that first. After that, get out your ohm meter and start checking the windings for an open coil.

If it has bronze sleeve bearings (rather than ball bearings) the bearings are out of oil and have seized up. Take the ends off, clean out the bearings with steel wool, polish the shafts with fine emery cloth, oil up the lubricating felts and put it back together.

Sounds like you have a winding down to ground. Do the following with the motor disconnected. With a multimeter set to low ohms (usually 200), test between each winding terminal and the metal casing of the motor. If there is any reading on any of these then the motor is bad, do not use it. You may find that when it runs ungrounded that the casing becomes live at up to supply voltage.

All motors should be protected by an overcurrent device (MCB) in the consumer unit, and a residual current device (RCD or GFCI). Fixed appliances should ideally be on their own circuit with the MCB sized to suit the appliance. MCBs should be of type C or D to allow for inrush current, and the Z ratings of the circuit must be below the specified threshold in your locality for the rating of the overcurrent device. 3 Phase motors are usually additonally protected by a thermal overload relay or electronic equivalent which is much more accurate and the same device can be used for single phase if desired.

It really shouldn't matter, an AC single-phase motor can be connected either way.

Apply a clamp meter to the “hot” wire (usually the black wire) and see how many amps the motor is drawing.

It's drawing more current than its rated capacity due to more load. Reduce the load.

It really depends on the motor windings , each motor is manufactured different. Typically you should see above 1 and below 30. Never 0 or open. When you really need to know the exact resistance, the best way is to contact the manufacturer, give them your motor model number and voltage setting, and they should give you a resistance range you should expect to see.

Zero ohms is what you're shooting for in any open/close contact switch, whether it's a simple light switch or an overload switch. One to two ohms is typical, three to five ohms is about the max. Some people may push for higher numbers, but I've seen too many failures soon after. Overload switches are directly at a disadvantage by nature because they are constantly subject to the thermal stresses in an electrical circuit. Thus they are prone to failure due to factors outside of their design and break down physically, causing higher resistance across their contacts.

Using an ohmeter set in the lowest range in ohms, check the resistance of the start winding (auxiliary) and the common terminal. Do the same with the run (armature) winding. You should have some reading. It not. then the motor windings are faulty or broken inside.

You can you an ohm meter or a simple bell circuit. Then check for an electrical connection between the motor frame and incoming electrical system ground. The reading should be very close to zero.

Sometimes they will spark because a gap is forming, making the electric ARC "jump the gap." This can also happen when the brushes are stuck and need cleaning because of low use,

An electric motor overheating could have many reasons, so check all points carefully. 1) Check for applied voltage range match with rated voltage of the motor on the name plate. 2) Check for full load current or overloading, match with rated current. 3) Check for cooling system (i.e. cooling fan) damage. 4) Check for motor bearing both side DE & NDE side damage. 5) Check coil winding of motor for improper insulation.

Check that the fuse size is correct against the motor rating. Check that the spindle/bearings are smooth in rotation and the rotational load connected does not provide excessive resistance. Remember, a motor that cannot turn is a short circuit. The slower the spindle turns, the greater the current flow through the circuit.

Capacitors will also limit current. They can be used to store voltage or build it up until the call for it to be released is present. A start capacitor is found in the circuit of start windings when the motor is starting. This capacitor contains a higher capacitance than a run capacitor.

The motor will only run if power is provided. If you take out (bypass) the switch, there's nothing to stop current from reaching the motor. It sounds like a bad switch. Disconnect the service power to the unit, then remove all wires and check the switch with an ohm meter. If it's bad, replace it. I don't recommend using the lathe without the ability to turn it off while operating it.

The armature is called a "rotor" in a brushless motor. A rotor is made from magnets and a laminated steel core. Rotors go bad from overheating. A bad rotor will be discolored in places (not silver). Overheating may be caused by misalignment. In this case the rotor is rubbing against the stator. The most common cause for misalignment is the housing or assembly being warped or distorted. Number 2 cause is the motor having been incorrectly assembled. Number 3 cause is the electronics/stator going bad. My practice as a power tool repair technician is to replace the rotor and the stator.

Specifically it might be on the bearings, whether they are greased in a good manner and aligned correctly.

Try a potentiometer or variable speed switch to adjust the speed. Sometimes, also, grease builds up in range hoods and makes them sluggish.

No, amperage depends with the voltage received through each of the three phases.

Check the connection. Out of 3 phases one phase is loose. You can use a clamp-on ammeter to locate the line that is not drawing current in the three-phase motor. After you have determined which line is not drawing current, you can look for a problem, such as an open wire or open fuse. It's important to remember that if the motor continues to try to start, additional fuses may also blow and the motor will no longer hum.

Most likely. There may be obstructions to airflow that prevent the heat from being carried away from the motor. There may also be an obstruction in the vacuum suction or discharge paths, causing the motor to have a continuous load greater than it was designed for.

Assuming this is a simple 3 lead motor, I would expect single-digit (1 to 9 ohms) resistance readings from all three combinations of test combinations. These measurements should reveal equal values of resistance within 20% or so between the highest and lowest value.

The motor is overloaded or is breaking down internally. This motor should be removed from service and either repaired, replaced or the load checked. If the load has changed, a motor sized to handle the load should be selected to replace the original.