4
connection to the circuit under test is essential to avoid mea-
surement errors. Circuits connected in parallel to the circuit
under test may also effect the accuracy of the measurement.
Possible insulation resistance measurement errors may be
caused by the circuit under test being wet and/or dirty. Errors
may also occur when testing large installations where the insu-
lation resistances may effectively be in parallel.
All fuses in or circuit
breakers closed
Mains switch open
Equipment disconnected
Note: Insulation testing must only be undertaken on
de-energised circuits.
Switches
closed
Lamps out
Reading not less
than 0.5 M
Ω
Main
switch
open