14.2.6 Test inhibit
The impedance test will be inhibited for several reasons, such as if:
The supply voltage is outside the acceptable range (48 V AC to 280 V AC for nominal 230 V supplies
and 376 V AC to 550 V AC for nominal 400 V AC supplies),
The supply frequency is outside the acceptable range (45 Hz to 65 Hz for nominal 50 Hz or 60 Hz supplies).
The touch voltage exceeds 25 V or 50 V depending on the Setup configuration
You can change the touch voltage limit to 25 V in set up Refer to 15.9.2 Maximum touch voltage on page 86.
14.3 Hot keys for Loop Impedance tests
Hot key 1 Hot key 2 Hot key 3 Hot key 4 Hot key 5
Fig 48: Loop impedance Hot keys
Hot key Function Description
1 Measurement type
Press repeatedly to select the type of measurement.
The options are:
Impedance (Z),
Maximum impedance (Zmax),
Reference impedance (Zref), for R1+R2 and Vdrop measurements
Internal impedance (R1 + R2),
Voltage-drop and (i-vdrop). The R1 + R2 and the I-volt drop options
are only available under certain conditions, Refer to 14.10 Zref –
making and using the reference impedance for R1+R2 and Vdrop
calculations on page 71.
2 Circuit protection
Press repeatedly to select the type of circuit protection.
The options are: NO RCD, RCD, RCD EV
3 Help/Save
Before starting a test, press for help on Loop Impedance testing.
When the test is complete, press to transfer the results if the MFT is
connected to a to a Bluetooth
®
device running CertSuite™. Refer to 16.
Download results to a remote device on page 89.
4 Test type
Press repeatedly to select the type of test.
The options are: 2 wire, 2 wire HR, and 3 wire. The 3 wire option is the
preferred option for circuits with RCD protection.
5 Test configuration
Press repeatedly to select the test configuration.
The options are L-PE, L-N, L1-L2, L2-L3, L3-L1
14.4 Test-lead null
To ensure best accuracy in a loop test, the MFT-X1 allows the test-lead resistance to be nulled. This prevents the lead
resistance from adding to the Loop Impedance. The MFT-X1 uses the continuity test-lead null to achieve this.
When a test-lead is nulled in the continuity mode, the same value is used in the Loop Impedance mode.
This allows different lead types to be used and quickly nulled.
For lead nulling procedure, Refer to 7.2 Continuity testing on page 28.
www.megger.com MFT-X1
65
Earth Loop Impedance testing – TrueLoop™
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