Kyoritsu 6010B User Manual download pdf (Page 21)

7.4 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

only be carried out after the mains supply has been connected. KEW 6010B

takes a current from the supply and measures the difference between the

unloaded and loaded supply voltages. From this difference it is possible to

calculate the loop resistance. 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

LEDs ARE LIT TO CONFIRM THAT THE WIRING IS CORRECTLY

CONNECTED. Should these two LEDs 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．Power on the instrument.

2．Set the function switch to Loop 20Ω range.

3．If testing sockets, connect the plug lead to the KEW 6010B and push the

moulded plug into the socket to be tested (see Fig 11).

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

5．Note the mains voltage displayed by the instrument.

6．Press the 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 Model 7133

(OMA DIEC :optional accessory) to KEW 6010B, 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 12).

8．If any RCD associated with the circuit trips out, reset the RCD and try

testing again, this time operating the 0°/180°select 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 20Ω the over-range symbol "OL"

will be displayed. If this is the case, switch the instrument up a range to the

2000Ω range and repeat the test to obtain a satisfactory reading. If the

instrument is set to the Loop 2000Ω range, the test will be carried out at the

reduced current of 15mA flowing. This setting will be very unlikely to trip out

the circuit RCD.

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Kyoritsu 6010B User Manual Page 21

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