SIM-Q MKII
Installation/operation instructions
DEIF A/S
Page 18 of 18
5.2
Leakage capacitance in a disconnected network
Measuring of the leakage capacitance in a disconnected network using a mA meter, a voltmeter
and an AC source with a known frequency.
CE total = mA/(V × 2 × phi × f). Phi = 3.14 and f is the frequency in Hz.
In the example below, the mA is measured to 100 mA and the voltage from the AC source is
measured to 50 V AC:
CE total = 0.1 A/50 V × 2 × 3.14 × 50) = 6.3
μF.
5.3
Leakage capacitance using the SIM-Q MKII fault finding function
The fault-finding function of the SIM-Q MKII can be used to estimate the size of the leakage
capacitor. Notice that this method can only be used when no insulation error is present.
Set the switch in fault finding position.
Discharge the leakage capacitor by short-circuiting P and PE by means of a low impedance load,
for example a bulb suitable for the AC voltage level on the system.
Open the short circuit between P and PE. Then measure the time (t) that elapses until the
instrument indicates approximately 0.5 (0.05) M
Ω
on the scale.
By using the formula C = t/0.3, the approximate
leakage capacitor in μF can be calculated.
Example: t = 10 seconds, C = 33
μF.
