Operation Manual

20 GMC-I Messtechnik GmbH
I
T
Touch Current – Testing for Absence of Voltage
Applications
For protection class I devices, it may be necessary to separately
measure leakage current from exposed conductive parts which
are not connected to the protective conductor.
Only methods direct measurement and differential current mea-
surement can be used for devices for which isolation in the power
pack is not taken into consideration by the measurement (e.g. re-
sulting from a relay which is only closed in the operating state).
Leakage current measurement may only be performed at
protection class I devices after the protective conductor test has
been passed.
The device must be measured in all intended functional states
(e.g. switch positions) which influence leakage current. The
highest acquired value, as well as the corresponding function if
applicable, must be documented. The manufacturer’s
specifications must be adhered to.
Definition of Touch Current
Leakage current that flows from the housing or parts thereof –
with the exception of the patient ports – with which the user or the
patient may come into contact during use for intended purpose,
to ground or another part of the housing via an external
connection, except for the protective conductor.
Definition of Direct Measurement
Current which flows through the probe in the case of housings
which are isolated from ground.
Definition of Differential Current Measurement
Sum of instantaneous current values which flow via the L and N
conductors at the device mains connection. Differential current is
practically identical to fault current in the event of an error. Fault
current: Current which is caused by an insulation defect, and
which flows via the defective point.
Definition of Alternative Measurement (alternative equipment leakage
current)
Alternative leakage current is current which flows through the
active conductors of the device which are connected to each
other (L/N), to the exposed, conductive parts.