KaVo ORTHOPANTOMOGRAPH OP 3D Service Manual page 157

2. Measure protective earth resistance between the mains cord plug earth and
measurement points specified in the previous step using the opposite polarity of the
measurement equipment.
With permanent power cord:
3. Measure protective earth resistance between the protective earth connection
in mains line (see figure 1 in
measurement points spcified above
4. Check that the protective earth resistance is less than 300 mΩ.
5. Record the highest value.
Leakage current measurement
NOTICE! The leakage current measurement can be performed only after the
protective earth measurements have been completed with passed results.
The purpose of the leakage current measurement is to verify that there are no leakage
currents, which would exceed the allowed limits, flowing from the mains parts via the
accessible conductive parts or the applied parts of the unit to the earth.
Leakage currents that exceed the allowed limits indicate that there is a failure either in
the unit's connections or in the device itself, and that the device is potentially unsafe to
use. If the leakage current measurement fails, the use of the unit must be stopped until
the unit or its installation has been repaired and confirmed to meet the requirements.
NOTICE! Steps 4 and 5 in the following chapter (Measuring leakage current)
apply only to cases where the polarity of the mains plug can be changed to
opposite. This may not be possible in permanent installation.
The measurement circuit principle for the direct method is shown in the figures (1 for
detachable power cord, 2 for permanent power cord) below:
Measuring leakage current
NOTICE! Steps 4 and 5 apply only to cases where the polarity of the mains plug
can be changed to opposite. This may not be possible in permanently installed
connection.
1. Connect the measurement device (MD). See the figures in chapter
measurement.
2. Measurement in power OFF condition:
a) Ensure that the main power switch of the unit is in OFF position.
b) Record the leakage current reading given by the MD.
ORTHOPANTOMOGRAPH
NOTICE! In measurements done according t figure 1 in
measurement set-ups, the resistance of protective earth connections in the
supply main may be taken into account.
NOTICE! With permanently installed power cord, additional test cord may be
required, see figures in
™
OP 3D
Principles of the measurement set-ups
Leakage current measurement.
8 Part replacement instructions
and the
Principles of the
Leakage current
157