13
Loop Impedance (Line to Protective Earth L-PE)
Loop impedance is source impedance measured between Line (L) and Protective Earth (PE).
You can also ascertain the Prospective Earth Fault Current (PEFC) that is the current that
could potentially flow if the phase conductor is shorted to the protective earth conductor.
The tester calculates the PEFC by dividing the measured mains voltage by the loop
impedance. The loop impedance function applies a test current that flows to earth. If RCDs
are present in the circuit, they may trip. To avoid tripping, always use the Zl No Trip function
on the rotary switch. The no trip test applies a special test that prevents RCDs in the system
from tripping. If you are certain no RCDs are in the circuit, you can use the Zl Hi Current
function for a faster test.
Note:
If the L and N terminals are reversed, the tester will auto-swap them internally and
continue testing. If the tester is configured for UK operation, testing will halt. This condition
is indicated by arrows above or below the terminal indicator symbol (
).
To measure loop impedance no trip mode:
W
Warning
To prevent tripping RCDs in the circuit:
• Always use the
position for loop measurements.
• Preload conditions can cause the RCD to trip.
• An RCD with a nominal fault current of 10 mA will trip.
Note:
To do a Loop impedance test in a circuit with a 10 mA RCD, we recommend a trip time
RCD test. Use a nominal test current of 10 mA and the factor x ½ for this test.
If the fault voltage is below 25 V or 50 V, dependent on the local requirement, the loop is
good. To calculate the loop impedance, divide the fault voltage by 10 mA (Loop impedance
= fault voltage x 100).
1. Turn the rotary switch to the
position.
2. Connect all three leads to the L, PE, and N (red, green, and blue) terminals of the tester.
3. Press F1 to select L-PE. The display shows the Z
I
and
indicator.
4. Before you do a loop impedance test, use the zero adapter to zero the test leads or the
mains cord. Press and hold
for more than two seconds until the ZERO annunciator
appears. The tester measures the lead resistance, stores the reading in memory, and
subtracts it from readings. The resistance value is saved even when the power is turned
off so it is unnecessary to repeat the operation each time you use the tester with the
same test leads or mains cord.
Note:
Be sure the batteries are in good charge condition before you zero the test leads.
5. Connect all three leads to the L, PE, and N of the system under test or plug the mains
cord into the socket under test.
Figure 7. Display After Zeroing
