This method statement outlines the procedure for conducting megger testing on power cables and branch circuit wiring.
Megger testing is an important step in ensuring the electrical integrity and safety of wiring systems. This document guides equipment, preparation, testing procedures, and reporting.
A. Megger Testing Equipment
- Megger Instrument Calibration
- The megger instrument used for testing must have valid calibration to ensure accurate results.
- Megger Testers
- Two types of megger testers will be used:
- Megger with a range of 500V for wire testing.
- Megger with a range of 1000V for cable testing.
B. Pre-Test Preparation
- Check Lead Integrity
- Ensure that the leads used for connecting the megger to the circuit are free from faults. Verify electrical continuity by touching the free ends of the leads together while the megger button is pressed ON to confirm zero resistance.
- Inspect PVC Adapters
- Verify the presence of PVC adapters for cables and male adapters for all PVC conduits terminating in the panel board.
- Verify Wiring Dressing
- Confirm that the dressing for all wires in the panel boards is complete and tidy.
- Confirm All Connections
- Ensure that all electrical connections are completed before proceeding with testing.
C. Electrical Continuity Test
- Test Setup
- Connect the free megger test probes to any two conductors that need to be tested.
- Conduct Test
- With all appliances connected or the two ends of the conductors shorted, and all switches turned ON, the megger reading should be zero. If the reading shows infinity, it indicates an open circuit, which needs to be traced and rectified.
- Cable Testing
- For cables, shorten the extreme ends of any two phases and conduct the test. The reading should be zero. If the megger reads infinity or a value in mega ohms, there is a fault in the cable that requires rectification. Repeat this procedure for the other three conductors of the cable.
D. Short Circuit Test / Insulation Resistance Test
- Test Setup
- Use a megger with a 500V range.
- Conduct tests between:
- Phase and neutral.
- Phase and earth.
- Neutral and earth.
- Conduct the test with the other ends of the circuit conductor open. The value should be infinity for all tests. If the value is zero, it indicates a short circuit or damaged wire insulation, necessitating replacement.
- Test Setup
- Use a megger with a 1000V range.
- Keep both ends of the cable open.
- Conduct tests between phases and neutrals as follows:
- R to Y
- R to B
- Y to B
- R to N
- Y to N
- B to N
- All these readings should be infinite. Any other value suggests a fault in the cable cores/phases that requires rectification.
The test results must be recorded in a specified format for reference and record-keeping by the engineers.
This format should be submitted to the consultant for approval before conducting the megger testing operation. Proper documentation ensures transparency and accountability in the testing process.
Here is the sequence of Testing and Commissioning in the construction projects.
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