14. After each test, the display shows the Loop Impedance (ZL-
PE) and the prospective earth-fault current, IPEFC, for the
most recent test.
It also shows Zmax, which is the highest value of impedance
measured in any of the tests.
15. After each test, the displays shows the Loop Impedance
(ZL-PE) and the prospective earth-fault current, IPEFC, for the
most recent test.
It also shows Zmax, which is the highest value of
impedance measured in any of the tests.
16. The Zmax value is stored until any Hot key setting is
changed.
14.10 Zref – making and using the reference impedance for R1+R2 and Vdrop
calculations
Zref is used in the R1+R2 and V-Drop test modes and MUST be stored before these tests can be run.
For R1+R2 measurements Zref is usually the L-PE measurement at the point the supply enters the building.
For Vdrop, the Zref is normally the L-N or L-L measurement at the point the supply enters the building.
Zref is usually the external Loop Impedance of a circuit but can include all of a circuit up to the final section closest to
the load.
In R1+R2 and V-Drop modes the Zref value is deducted from the total circuit impedance to leave only the final circuit
or R1+R2 Loop Impedance, or the V-drop of the circuit excluding the Zref part.
Zref is always stored automatically. It will only appear in test modes that require Zref and be displayed in the lower
left of the screen.
1. Turn the left-hand rotary knob to the Loop Impedance test
position (Z).
1.1. The display illuminates with a green background.
2. Plug your L (red) test-lead into the red socket and your PE
(green) test-lead into the green socket.
3. Repeatedly press Hot key 1 to select Zref.
3.1. Alternatively, press Hot key 1 once and use the right-
hand rotary knob to select Zref.
www.megger.com MFT-X1
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Earth Loop Impedance testing – TrueLoop™
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