METREL MI 3399, Инструкция с упражнениями

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Electrical Installation Safety Trainer AD 1 - MI 3399
91
Figure 2-34: Insulation resistance measurement at the switchboard
– disabling
circuits during measurement
2.6.1 Background of measurement
This test discloses insulation faults caused by pollution, moisture, deterioration of
insulation materials etc. The insulation resistance shall be measured between

Line conductors.

Line and PE conductors.

Line and neutral conductors.

Neutral and PE conductors.
Nominal circuit voltage
Test voltage
(V DC)
Insulation
resistance (M
Ω)
SELV and PELV 250

0.5
Installations with nominal voltages up
to and including 500 V, including FELV 500

1.0
Above 500 V 1000

1.0
Table 2-2: Insulation resistance limits

Capacitances in the installation (cables, connected equipment) can cause
capacitive leakage currents. The capacitive portion of the impedance is not
considered in the insulation test as it is carried out with DC current.

In normal cases, the insulation resistance is far higher than predefined limits,
especially in new installations. When the result is close to or less than the required
minimum insulation resistance:
- Repeat the measurement with a longer measurement time or perform a couple
of test.