Setting precision:- 10 - 50 mA 1 mA steps
50 - 500 mA 5 mA steps
500 mA - 1000 mA 10 mA steps
RCD Type
Pressing the TYPE key displays the RCD type symbols. From
information given on the RCD to be tested, select and set the
type of RCD.
D.C. Sensitive relays
Some RCDs are electromechanical devices which can be
saturated by the presence of d.c. Therefore if a d.c. fault occurs,
or an a.c. fault occurs in the presence of quite a small direct
current, the RCD may not trip. In this way the RCD is disabled
and this becomes a potential hazard. Because of this, ‘d.c.
sensitive’ RCDs are available.
Selective or Time delayed RCDs
In some cases it may be necessary to have an RCD protecting
an individual circuit or group of circuits. If a fault occurs, the RCD
nearest to the fault should trip to clear it, maintaining supplies to
the other circuits. Selective RCDs (normal symbol )are used to
discriminate faults occurring on separate circuits, and these have
a minimum as well as a maximum trip time.
Type of test
19
Symbol
Test
General
Selective (delayed)
D.C. Sensitive
Display
1
⁄2I
0˚
180˚
5
I
Type of Test
No Trip
Trip Test
Trip test
Ramp test
Trip Test
Description
Performs a no-trip test at half the
rated current of the selected RCD.
The test measures the earth loop
resistance and contact voltage, or
with a test spike, the earth
resistance and fault voltage.
Trip test at the rated current of the
selected RCD. A
1
⁄2I test is carried
out before this, and the resistance
and voltage are available after the
test. The test is always started on a
zero crossing when the
instantaneous voltage is on the rise.
As above, but the test is always
started on a zero crossing when the
voltage is on the fall.
Test current increases from half the
rated current of the RCD. The result is
the current at which the trip opens.
Trip test at 5 X the rated current of
the selected RCD. The choice of 0˚
or 180˚ gives greater accuracy of
measurement.A
1
⁄2I test is carried
out before this, and the resistance
and voltage are available after the
test.
Ramp and Auto sequence tests are only available if
the test current is set to 10 mA. The maximum possible
test current (including
5I multiplier) is 1000 mA (300 mA
for d.c. sensitive RCDs). These limits are halved if the
supply voltage is less than 200 V.
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