how is IR value calculated?

Inroduction 

The measurement of insulation resistance is measure requirement of all electrical equipment, electrical wire,cable.

This is often used as a customer acceptance test.

The results are obtained from IR test is intended to detect fault from insulation

Selection of IR taste value

insulation testers with test voltage of 500, 1000, 2500, and 5000 V are available

The recommended ratings of the insulation testers are given below

voltage level                   IR Tester

450V                                500V DC

650V                                500V DC

1.1KV                              1KV DC

3.3KV                              2.5KV DC

11KV                               2.5KKV DC

66KV AND ABOVE      5KV DC

EXAMPLE 

(1) for 11kv 3 phase motor

IR value =11+1=12 MΩ

BUT AS PER IEEE43 IT SHOULD BE 100 MΩ

(2)for 415 V 3 phase motor

IR value=415+1=1.41  MΩ

BUT AS PER IEEE43 IT SHOULD BE 5  MΩ