Kyoritsu 4300 Manuale Utente Scaricare il pdf (Pagina 17)

8. Earth resistance measurement

This instrument can measure the earth resistances of distribution

line, internal wiring and electrical appliance.

DANGER

● Never apply inputs exceeding 300V between the measuring

terminals at earth voltage measurements.

● No voltage should be applied between the measuring terminals

during earth resistance measurements.

8-1 Principle of measurement

This instrument carries out earth resistance measurements based

on the fall-of-potential method. This is a simplified earth resistance

tester and uses the existing earth systems (with a sufficiently

low earth resistance) such as buried metal pipes like main water

pipe, common earth for commercial power supply and a lightning

electrode on buildings and performs measurements based on the

2-pole measurement method.

The AC constant current

“I” is applied between the

measurement object “Rx”

(earth electrode) and the

existing electrode “re” to

obtain the earth resistance

value “Rx + re” and find out

the voltage “V” between the

E and H+S(C+P) terminals.

See Fig. 8-1.

Rx + re = V / I

The resistance “re” of the existing earth electrode with which

H+S(C+P) terminal is connected is added to the true resistance

“Rx” of the measured object, and displayed as the measured result.

Re (measured value) = Rx + re

If the value of “re” is already known, deduct it from the measured

value “Re” to determine “Rx” value.

Rx (true resistance value) = Re – re

H+S (C+P)

terminal

Voltmeter

Earthing system

under test

Earth electrode

Constant current

generator

Secondary

Primary

I→

Fig. 8-1

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Kyoritsu 4300 Manuale Utente Pagina 17

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