Residual Voltage - LEM MachineTest 204 Manuel D'utilisation

MEASUREMENTS

4.3 Residual voltage

Purpose of the measurement is:
• To check if there is no hazardous voltage at mains one-phase or three-phase
plug after pulling out the plug (wall-plug connected machines).
• To check if there is no hazardous voltage at any accessible electric
component inside the tested machine after switching off the machine (wall-plug
and permanently connected machines).
Safe conditions must be assured with appropriate electric and/or mechanic construction
of tested machine. The conditions must be assured also during the machine is powered
but we must be aware that some components can become accessible only after de-
energizing the machine e.g. plug pins or components behind electrically blocked
barriers.
Test of residual voltage is to be done only if there is an electric charge present
higher than 45µ µ C, otherwise the charge may be considered as safe one.
Measurement principle
V
Fig. 10: Residual voltage measurement principle
Residual voltage measurements of AC voltage can be carried out in linear mode or non-
linear mode – see next page for detailed explanations.
U
Fig. 11. Graphic presentation of U
inside tested machine (AC voltage)
_
∼
+
∼
coincidental switch off
at any mains voltage
1s / 5s
1s / 5s
in case of measurement at mains plug or
RES
60 V d.c.max
after 1s
all combinations
among mains plug
terminals
U (correct value)
RES
U
RES
14
60 V d.c.max
after 5s
C
L1
L2
L3
N
PE
PE collector
t