METHOD STATEMENT MEGGER TESTING FOR POWER CABLES & BRANCH CIRCUIT WIRING
EQUIPMENT AND TOOLS:-
1. Megger Instrument shall be having valid calibration.
2. Megger-with range 500V/1000V shall be used for conducting the test.
Megger range 500 V shall be used for Wire testing
Megger range 1000 V shall be used for Cable testing
PRE – TEST PREPARATION:-
1. The leads used for connecting megger with the circuit should be fault free and the two connecting leads should have electrical continuity. It is checked by touching the free ends of the leads together while the megger button is pressed ON to check for zero resistance.
2. Check for PVC adopters are provided for cables and male adaptor for all PVC conduits terminating in the panel board.
3. Check the dressing is complete for all the wires in the panel boards
4. Confirm all the connections are completed before the testing.
ELECTRICAL CONTINUITY TEST;-
1. Connect the free megger test probes to any two conductors required to be tested.
2. With all the appliance connected or the two ends of the conductors shorted and all Switches switched ON the reading shown on the megger should be zero. If the reading shows infinity then there is an open circuit. The fault should be traced and rectified.
3. For cables, the extreme ends of any two phase is shorted and when the test is conducted the reading should be zero if the meter reads infinity or some value of mega ohms then there is a fault in the cable and it should be rectified. Same procedure shall be repeated for other 3 conductors of the cable.
SHORT CIRCUIT TEST / INSULATION RESISTANCE TEST;-
FOR WIRES;
1. For wires the circuit is tested, Megger range should be 500V
I. Between phase and neutral.
II. Between phase to earth
III. Between neutral to earth
With the other ends of the circuit conductor open the value should be infinity for all the test. If the value is zero there is short circuit or the insulation of the wire is damaged and the wire is changed accordingly.
FOR CABLES:-
For Cables the Megger range should be 1000V, and both the ends of the cable shall be kept open and test shall be conducted between phases and neutrals as follows:
neutrals as follows:
| i. | RtoY |
| ii. | RtoB |
| iii. | YtoB |
| iv. | RtoN |
| V. | YtoN |
| vi. | BtoN |
all these reading should be infinity, if otherwise the cable ^ores/phases are faulty and should be rectified.
The test results shall be recorded in a format for Engineers reference and record. The format shall be submitted to Consultant for approval in advance prior to perform the megger test operation.
