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8.10 Type B (Pure DC) RCD test (MFT1825 and MFT1835 only)
‘Type B’ RCDs are sensitive to pure DC fault currents, as well as pulsed AC and ordinary AC fault currents. First they are tested as Type
AC, Type A then type B., using a pure DC test current.
Type ‘B’ RCD’s are only tested on the 1xI range. The result displayed in milli-seconds (ms).
.1 Test the RCD in ‘type A’ mode for 1/2xI , 1xI and 5xI if it is a 30mA RCD. Test it in 1xI only if it is > 30mA.
.2 To select a Type B RCD press and hold the mode button <-> repeatedly until the
symbol is displayed.
.3 Connect the Red L1, Green L2 and Blue L3 terminals of the MFT to the RCD Live, Neutral and Earth as below (‘type AC’ and
‘type A’ RCD’s only need Phase and Earth connections).
RCD
g
L
N
E
MCB
.4 Select the 1xI range on the left range knob, and the current rating of the RCD on the right range knob.
.5 Press the TEST button.
.6 The RCD should trip and display the trip time in ms. The “Touch Voltage” is displayed on the small digital readout.
Notes:
Only 1 x I is available. Selecting other test currents will reset the test type to AC.
Only 10mA, 30mA, 100mA and 300mA test options are available on DC testing.
The tripping current of a type B RCD can be measured by performing a ramp-test as type B
8.11 Variable RCDs (not MFT1815)
.1 To test an RCD with a variable trip current, select the
VAR
option on the secondary (right) range knob.
.2 Press the
MODE button to select the
symbol
.3 Use the UP and DOWN arrows on the right hand TEST and LOCK buttons to set the tripping current to match that on the
variable RCD.
The tripping current can be selected as below;
10mA to 50mA
– 1mA steps
50mA to 500mA
– 5mA steps
500mA to 1000mA
– 10mA steps
.4 Save this current using the left hand LOCK button.