Megger testing measures resistance between the phase windings of the motor under test and ground. If there is an insulation breakdown, the resistance is negatively impacted and there is a departure between phases or between one measurement and a previous one and a determination of motor health is made.
What readings should you get when Megging a motor?
The rule may be stated: Insulation resistance should be approximately one megohm for each 1,000 volts of operating voltage, with a minimum value of one megohm. For example, a motor rated at 2,400 volts should have a minimum insulation resistance of 2.4 megohms.
How do you know if a 3 phase motor is bad?
Using a multimeter, check the continuity of motor winding from phase to phase ( U to V, V to W , W to U ). 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.
What is a bad Meg reading?
If the megger reads a resistance under 1 (1,000 ohms) on your meter after the initial 60-second interval, the cable has failed and the cable should be removed. If the megger reads a resistance between 1-1.25 on your meter, then the cable passes. Any reading above 1.25 is considered excellent.
What is a bad megger reading on a motor?
The measurement of insulation resistance is carried out by means of a megohmmeter – high resistance range ohmmeter.
A general rule-of-thumb is 10 Megohm or more.
|Insulation resistance value||Insulation level|
|2 Megohm or less||Bad|
Can a Megger kill you?
Although Megger insulation testers are NOT inherently dangerous, safety officers and safety S.O.P.s often call for added diligence above 500 V. Time is an important test variable in insulation testing, much more so than in many familiar electrical tests.
How do I know if my Megger is working?
Press the test button on megger, the megger will generate current. This current flows through cable, the resistance in scale is noted which ranges between 35 to 100 Mega Ohms. Note to maintain this contact for 30 to 60 seconds. Acceptable IR for electrical cable = 1 Mega Ohm for 1000 V.
Can a megger damage a motor?
Never use a megger if the motor windings are under a vacuum. … A high voltage for too long of a time may further weaken or fail motor windings and the winding insulation could be damaged by the testing procedure.
How much resistance should a motor have?
Earth Continuity and Resistance Test
A good motor should read less than 0.5 ohms. Any value greater 0.5 ohms indicate trouble with the motor.
Can you meg a DC motor?
Connect one lead of the DC motor to the megger probe and the other lead from the megger to the frame or metal case of the DC motor. Press the power button on the megger or turn the hand crank. The battery unit will take a few seconds to analyze the voltage travel and soon a reading should appear on the LCD screen.
How do you check if a motor is working?
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.
How do you check if a motor is grounded?
Using Ohm meter: Disconnect all power from machine. Check all three wires singly T1,T2,T3 (all three phases) to the ground wire. Readings should be infinite. If its zero or reads any continuity at all, then a problem exists with either the motor or cable .
Why is my 3 phase motor humming?
If the motor hums but won’t turn when power is applied, it indicates that one phase of a three-phase motor is open, or the start winding of a single-phase motor is open. … This problem may be caused by having too large a load for the motor or a bearing that needs lubrication.