17
3.4. INSULATION RESISTANCE MEASUREMENT
3.4.1. DESCRIPTION OF THE MEASUREMENT PRINCIPLE
The device generates a DC test voltage between the COM and M
W
terminals. The value of this voltage depends on the resistance
to be measured: it is greater than or equal to U
N
when R is greater than or equal to R
N
= U
N
/1 mA, and less otherwise. The device
measures the voltage and current present between the two terminals and from them deduces the value of R = V / I.
The COM terminal is the voltage reference point. The M
W
terminal therefore provides a negative voltage.
3.4.2. MAKING A MEASUREMENT
The alarm, if activated, serves to inform the user, by an audible signal, that the measurement is below threshold, making it un-
necessary to look at the display unit to check this point.
SET UP
OFF
R
Set the switch to M
W
.
Use the leads to connect the device to be tested between the COM and M
W
terminals of the device. The object to be tested must not be live.
To avoid leakage during the insulation measurement, which would
throw off the measurement,
do not use
the measuring cable when
you make this type of measurement, but two simple leads.
Generally, an insulation measurement on an installation is made between the interconnected phase(s) and neutral, on the one
hand, and earth, on the other.
L3
PE
N
L1
L2
If the insulation is not sufficient, you must then make the measurement between each of the pairs to locate the fault.
The remoted
TEST
button of the optional remote control probe makes it easier to trigger the measurement. To use the remote
control probe, refer to its user’s manual.
L3
PE
L1
L2
Operation only
with
C.A 61
13/16/17
