for two seconds.
Method of measurement
The two wire lead or plug should be used for this measurement. A
constant current source is connected across the supply and the time taken
for the supply to trip is measured by the instrument in ms.
Possible sources of error
Measurement results can be affected by the following:
■ Significant operating errors can occur if loads, particularly rotating
machinery and capacitive loads are left connected during tests.
■ A poor connection to the circuit under test.
Thermal Protection
T
The RCD circuit has thermal protection fitted to prevent overheating in
the event of multiple ramp tests being performed. The T symbol or the
message "Hot" will be displayed. Allow the instrument time to cool down
before continuing.
16
3. Press the YELLOW TEST button
4. The trip current is displayed.
5. If the RCD fails to trip, ">***mA" will be displayed, where
*** indicates the last test current applied.
DC SENSITIVE RCD TESTING
D.C. sensitive RCDs are tested with a pulsed waveform. The RMS current is
√2 x the rated operating current of the RCD. As with the normal RCDs,
these should be tested with 0° and 180° polarity.
1. Select the appropriate RCD rated current on the right hand
rotary switch.
2. Select the [1/2I, I, or 5I] test on the left hand range knob
3. Use the BLUE button to cycle through the test options,
selecting DC and the required polarity.
4. Press the YELLOW TEST button
5. The trip time will be displayed in ms.
6. If enabled, the touch voltage will be displayed on the bar-
graph display.
7. If the RCD fails to trip, ">400 ms" will be displayed.
TIME DELAYED (SELECTIVE) RCDS
The selective RCD testing is enabled by a long press on the blue degree
button. As selective RCD test mode is enabled the MFT will emit a long
beep and the display will show the exclamation mark (!) symbol. Once the
selective RCD mode is chosen, testing of the RCDs can be performed in
the same way as normal RCDs (see above for Residual Current Device
(RCD) Testing, ). To disable selective RCD mode press the degree button
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