Velleman AVM52ERT Mode D'emploi page 4

5) Simplified Earth Resistance Measurement
This method is recommended when measuring an earth resistance > 10Ω or when it is
impossible to drive auxiliary earth bars into the ground. An approximate value can be obtained
through the two-wire system, which uses previously earthed devices (see fig. 3 below).
Note : Make sure that the earth is connected to terminal P when measuring earth resistance
through mains power (A).
Press the AC V button as outlined in "2) Earth Voltage Measurement of Earthed Equipment
under Test" to measure the earth voltage of the equipment under test and make certain that
earth voltage is below 2V.
Press the "x10Ω" button and then the MEAS. button. Read the earth resistance from the scale.
Press the "x100Ω" button if the needle tilts to the far right.
The obtained reading (RE) is a renders the approximate earth resistance value. There is no
need for external shorting as terminals P and C are shorted internally.
The earth leakage breaker will not trip because the measuring current is as low as 2mA.
The OK lamp is lit in the normal operation mode whether the simplified or the ordinary
measurement method is used (this indicates that continuity exists between the various terminals
E, P and C).
In case of the simplified measurement method only two terminals are used. The earth
resistance "re" of an earthed electrode connected to terminal P should be added to a true earth
resistance value REX. Therefore, the earth resistance reading is the result of the following
formula :
RE = REX + re
Fig. 3
Suppose that "re" is a known value :
Let us also assume that RE is 100Ω and that the earth resistance to be measured is e.g. 100Ω.
Consequently, the true earth resistance is expressed as :
REX = (100Ω) – re
Since re is greater than 0, a true earth resistance may be expressed as follows :
REX ≤ 100Ω
AVM52ERT 4 VELLEMAN