Megger MFT1815 - Page 5

6. Insulation resistance
500
V
.............................................................................................................. 24
6.1. Making an INSULATION measurement ..................................................................................................24
6.2. Insulation test lock ..................................................................................................................................25
6.3. Measurement methods and sources of error.........................................................................................25
7. Loop impedance testing ..............................................................................................................26
7.1. Range selection and test leads ...............................................................................................................26
7.1.1. Phase to earth L-E circuits ......................................................................................................................26
7.1.2. L-N or L-L circuits...................................................................................................................................28
7.1.3. Z, Zmax, Zref and R1+R2 .......................................................................................................................28
7.2. Making a loop impedance measurement ..............................................................................................28
7.2.1. Ze measurements at the origin (Phase to Earth) .....................................................................................28
7.2.2. Zs and Zdb loop measurements without RCD - eg Zs, Zdb etc. ...............................................................29
7.2.3. Earth Loop measurements with an RCD in circuit ...................................................................................30
7.3. Phase to Neutral (all models) or Phase to Phase testing .......................................................................32
7.4. Prospective Fault Current and Short Circuit calculation (PFC & PSCC) .................................................33
7.5. Confidence MeterTM for non-trip (3Lo) loop impedance tests ...........................................................34
7.5.1. Display information ...........................................................................................................................34
7.5.2. 3Lo Loop Impedance Measurement ..................................................................................................34
7.6. Measurement methods and sources of error.........................................................................................36
8. Residual Current Device (RCD) or Ground Fault Current Interrupt (GFCI) testing ...................37
8.1. Making an RCD measurement ................................................................................................................ 38
8.2. Selecting RCD type ..................................................................................................................................38
8.3. ½ x I RCD current rating (No-trip test)
........................................................................................39
8.4. 1 x I RCD current rating (Tripping test on 30 mA RCD) ....................................................................... 40
8.5. 2 x I RCD Current Rating (Tripping test on 30mA RCD) (Not MFT1815) ............................................41
8.6. 5 x I RCD current rating (Tripping test on 30 mA RCD) ....................................................................... 41
8.7. Ramp test
.......................................................................................................................................... 42
8.8. Fast Ramp Test ......................................................................................................................................... 42
8.9. Type A (DC Sensitive) RCD test
................................................................................................... 42
8.10. Type B (Pure DC) RCD test (Not MFT1815) ...........................................................................................43
8.11. Variable RCDs .........................................................................................................................................44
8.12. AUTO RCD testing .................................................................................................................................44
8.13. 3 Phase RCD testing ...............................................................................................................................45
8.14. Touch voltage display ............................................................................................................................45
8.15. Measurement methods and sources of error.......................................................................................46
8.16. Useful information ................................................................................................................................46
9. Testing of Electric Vehicle Charge Point RCD’s ........................................................................... 47
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