Kyoritsu 6010A User Manual download pdf (Page 19)

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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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Kyoritsu 6010A User Manual Page 19