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.
What is the purpose of a Megger?
The Megger test is a method of testing making use of an insulation tester resistance meter that will help to verify the condition of electrical insulation. Insulation resistance quality of an electrical system degrades with time, environment condition i.e. temperature, humidity, moisture and dust particles.
How many ohms should a motor read?
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.
What is a bad Meg reading?
When a motor reads 0 ohms this is a dead short or “grounded”, “Fried”. . We used a rule of thumb of anything under 20 megohms was bad. after that it was questionable until after 50 meg. When are readings went towards infinity we knew it to be good.
What should a good motor Megger?
A general rule-of-thumb is 10 Megohm or more.
|Insulation resistance value||Insulation level|
|50-100 Megohm||Very good|
|100 Megohm or more||Excellent|
Can a megger kill you?
Usual megger voltage is 500 V, and our body resistance can be 1 M or little less. This means a maximum current of 1 mA or bit more, which is not safe, though not fatal (If we don’t count meter resistance).
How do you read megger results?
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 the difference between megger and Hipot?
A megger is a megohmeter, measures insulation resistance. A hipot tester basically works the same way, but measures leakage current. If you see a fault with the megger, you will see a fault with the hipot. The hipot stresses the insulation weak points at higher voltage levels than the megger will.
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.
What does it mean to Meg a motor?
This is an insulation test of motor windings, commonly referred to as megging, to megger, or to meg a motor. We are testing the motor’s insulation, more specifically between the motor windings and the motor casing. … Using a megohmmeter properly will test any motor insulation.
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.
How many ohms should a 3 phase motor have?
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. It will usually be low enough (under 30 Ω) for the audible continuity indicator to sound.
How do you know if a motor is bad on a multimeter?
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 many ohms is considered a short?
Very low resistance — about 2 ohms or less — indicates a short circuit. In the case of a short, the resistance is typically considered to be zero.