The rule states that insulation resistance should be approximately one megohm for each 1000 volts of operating voltage, with a one megohm minimum. (By following this rule, a motor rated at 2400 volts should have a minimum insulation resistance of 2.4 megohms).
How much resistance should a motor have?
With a multimeter, measure the resistance between motor frame (body) and earth. A good motor should read less than 0.5 ohms. Any value greater 0.5 ohms indicate trouble with the motor.
What is the minimum insulation resistance of a 3 phase induction motor?
The minimum value of insulation resistance should be 1 megohm. If the value is less than 0.2 megohms, replace the motor.
What is a good Megger reading for a 480V motor?
IEEE recommends that for motor starting that the operational voltage, expressed as a meg-ohm value doubled plus 1000 is the minimum meg value for starting. For a 480V motor that would mean . 480Meg x 2= . 960 Meg + 1000, so a minimum ground resistance for starting a 480V is 1.960 Meg or round up to 2 meg-ohms.
What is the minimum value of IR?
1. IR Values For Electrical Apparatus & Systems
|Max.Voltage Rating Of Equipment||Megger Size||Min.IR Value|
|15 KV||2,500 Volts||5,000 MΩ|
|25 KV||5,000 Volts||20,000 MΩ|
|35 KV||15,000 Volts||100,000 MΩ|
|46 KV||15,000 Volts||100,000 MΩ|
How do you test an insulation resistance on a motor?
This is how the test works: DC voltage of 500 or 1000 V is applied between the windings and the ground of the motor.
A general rule-of-thumb is 10 Megohm or more.
|Insulation resistance value||Insulation level|
|50-100 Megohm||Very good|
What is motor winding insulation?
After a motor is rewound, the windings must be further insulated with resin or varnish. This insulation protects the windings from contamination, shorting electrically, and also make the windings more mechanically rigid.
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.
What is HV and IR test?
The high voltage system consist of generators, cables for power distribution, transformers, switch gear, and consumers. … In high voltage system, insulation resistance is measured using a 5000 volt DC megger, for voltages upto 6.6 kV. Furthermore, insulation resistance is measured under following conditions.
What is an acceptable resistance to ground reading for a 440v motor?
For most low voltage equipment, or those with voltage below 50 V, insulation resistance is measured at 100 V, for others including those working on mains, or voltages below 440 V, convention is to use 500 V measurement. For still higher voltages, insulation is measured at 1000 V.
What is the minimum insulation resistance for a 400v circuit?
Test voltage 500v for 230v or 400v installations or circuits with a minimum insulation resistance of 1 M ohm (1000,000 ohms).
What is the maximum insulation resistance?
For many years, maintenance professionals have used the one-megohm rule to define the allowable lower limit for insulation resistance. The rule states that insulation resistance should be approximately one megohm for each 1000 volts of operating voltage, with a one megohm minimum.
What is the insulation resistance?
The insulation resistance is the resistance in ohms of wires, cables and electrical equipment. It is important to guard against electric shocks and avoid equipment damage from accidental discharges. The method of measuring the insulation resistance is to test and assess the state of the isolation (head and body.)