HT instruments MACROTEST G3 - Manual (Page 93)

MACROTESTG3 - COMBIG3
EN - 92
12.4. TEST ON DIFFERENTIAL SWITCHES (RCD)
Purpose of the test
Checking that the General (G) and Selective (S) and Delayed ( ) differential protection
devices have been correctly installed and adjusted and that they maintain their
characteristics over time. The check must make sure that the differential switch trips at a
current not higher than its nominal operating current IdN and that the tripping time meets
the following conditions, according to the case:
 The tripping time does not exceed the maximum time as prescribed by the standard for
differential switches of a General type (according to what described in Table 4).
 The tripping time is between the minimum and the maximum tripping time for
differential switches of a Selective type (according to what described in Table 4).
 It does not exceed the maximum delay time (normally set by the user) in case of
Delayed differential switches.
The differential switch test performed with the test key helps so that no “gluing effect”
jeopardizes the operation of the device if it has remained unused for a long time. This test
is only performed to ascertain the mechanical functionality of the device and it is not
sufficient to declare the devices conformity to the standard regarding differential current
devices. According to statistics, switch verification through test key, if performed once a
month, reduces to a half the devices malfunction rate. However, this test only detects 24%
of the defective differential switches.
Parts of the system to be checked
All differential switches must be tested upon installation. In low-voltage systems, it is
advisable to perform this test, fundamental in order to guarantee a correct safety level. In
medical rooms, this test must be performed periodically every six months on all differential
switches as prescribed by the guidelines.
Allowable values
Two tests must be performed on each molded case RCD type: a test with a leakage
current beginning in phase with the positive half-wave of voltage (0°) and a test with a
leakage current beginning in phase with the negative half-wave of voltage (180°). The
result to be considered is the higher one. The test with ½In must not cause the differential
switch tripping.
RCD type IdN x 1 IdN x 2 IdN x 5 * Description
General 0.3s 0.15s 0.04s Maximum tripping time in seconds
Selective S
0.13s 0.05s 0.05s Minimum tripping time in seconds
0.5s 0.20s 0.15s Maximum tripping time in seconds
Table 4: Tripping times for general and selective molded case RCD type
Measurement of tripping current for protection differential switches

This test aims at checking the real tripping current of general differential switches (it
does not apply to selective differential switches).
 In the presence of differential switches with selectable tripping current, it is useful to
perform this test in order to check the real tripping current of the differential switch. For
differential switches with fixed differential current, this test may be performed in order to
detect possible leakages of the users connected to the system.
 Should an earth system not be available, perform the test by connecting the instrument
to a terminal on a conductor downstream of the differential device and a terminal on the
other conductor upstream of the device.
 Tripping current must be between ½Idn and Idn.