6． Loop Impedance Tests. KYORITSU 6010A

Below you will find brief information for Multi-Function Tester 6010A. This manual provides instructions on how to use the Multi-Function Tester 6010A to test continuity, insulation resistance, loop impedance, and RCDs. It also includes information on safety, battery replacement, and fuse replacement.

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6. LOOP IMPEDANCE TESTS

DISCONNECT THE INSTRUMENT FROM THE CIRCUIT UNDER TEST

BEFORE OPERATING THE FUNCTION SWITCH

TO SELECT THE LOOP TESTING RANGE SELECT

“LOOP”

6.1 Voltage Measurement

Press the test button once. Then, the instrument switches on.When the tester is set to the loop test function, mains voltage is displayed as soon as the instrument is connected for test. This voltage display is automatically updated five times every second. The voltage function operates whenever the test button is in the up position.

6.2 What is earth fault loop impedance?

The path followed by fault current as a result of a low impedance fault occurring between the phase conductor and earth is called earth fault loop.

Fault current is driven round the loop by the supply voltage, the amount of current depending on the voltage of the supply and on the impedance of the loop. The higher the impedance, the lower will be the fault current and the longer it will take for the circuit protection (fuse or circuit breaker) to operate and interrupt the fault.

To make sure that fuses will blow or that circuit breakers will operate quickly enough in the event of a fault, the loop impedance must be low, the actual maximum value depending on the characteristics of the fuse or the circuit breaker concerned. Every circuit must be tested to make sure that the actual loop impedance does not exceed that specified for the protective device concerned.

6.3 Automatic over-temperature cut-out

During the short test period the instrument dissipates power of about 6 kW. If frequent tests are conducted over a prolonged period of time, the internal test resistor will overheat. When this happens, further tests are automatically inhibited and the over-temperature symbol ( ) appears in the display. The instrument must then be left to cool down, when testing may be resumed.

6.4 The loop impedance test

Since the earth fault loop is made up of conducting path which includes the supply system back to the supply transformer, it follows that loop testing can

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only be carried out after the mains supply has been connected. In many cases, any RCD in the circuit will be tripped by this test, which draws current from the phase and returns it through the earth system. The RCD will see this as the type of fault it is designed to protect against, and will trip. To prevent this unwanted RCD tripping during loop testing, any RCD must be taken out of circuit and temporarily replaced with a suitably rated MCB unit. The RCD will need to be replaced after the loop test is completed.

WARNING

DO NOT PROCEED WITH TESTING UNLESS THE P-E AND P-N

LAMPS ARE LIT TO CONFIRM THAT THE WIRING IS CORRECTLY

CONNECTED. Should these two lamps not be lit, investigate the wiring connections of the installation and rectify any faults before proceeding with the test. If the LED is lit do not proceed.

1．Press the test button once. Then, the instrument switches on.

2．Set the instrument to loop test 20Ωrange.

3．If testing sockets, connect the plug lead to the Model 6010A and push the moulded plug into the socket to be tested (see Fig 9).

4．Check the wiring lamps are lit (see above).

5．Note the mains voltage displayed by the instrument.

6．Press the“Press to test”button. The value of the measured loop impedance will be displayed with the appropriate units.

7．If testing lighting or other circuits, connect the three-wire lead OMA DIEC to

Model 6010A, connect the red (phase) lead to the phase connection of the circuit under test, connect the black (neutral) lead to the neutral connection of the circuit under test, and connect the earth lead to the earth associated with the circuit. (see Fig 10).

8．If any RCD associated with the circuit trips out, reset the RCD and try testing again, this time operating the phase selector switch once prior to pressing the test button. This will change the period of the waveform over which the instrument performs the loop test. This may result in the RCD not tripping out. If the RCD still trips, temporarily replace it with a suitably rated

MCB for the duration of the test.

9．If the instrument measures greater than 20Ωthe over-range symbol“OL” will be displayed. If this is the case, switch the instrument up a range to the

2000Ωrange and repeat the test to obtain a satisfactory reading. If the instrument is set to the "loop2000Ω"position,the test will be carried out at

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Key features

Continuity tester
Insulation resistance tester
Loop impedance tester
RCD tester
Mains voltage warning
Auto discharge
Test current Warning Beeper
Voltage level
Wiring check
Over temperature protection

Frequently asked questions

The path followed by fault current as a result of a low impedance fault occurring between the phase conductor and earth is called earth fault loop. Fault current is driven round the loop by the supply voltage, the amount of current depending on the voltage of the supply and on the impedance of the loop.

The RCD is designed to trip out when the difference between the phase current and the neutral current (this is called the residual current) reaches the tripping value (or rating) of the device. The tester provides a carefully preset value of residual current depending on its setting and then measures the time lapse between the application of the current and the operation of the RCD.

RCDs rated at 30 mA or less are sometimes used to provide extra protection against electric shock. Such RCDs require a special test procedure. Set the "RCD"switch to "150 FAST". Connect the test instrument to the RCD to be tested. Make sure that the P-E and P-N wiring check lamps are lit. Press the test button to apply a test current of 150mA where the RCD should trip within 40ms.