COMBITEST422
EN - 104
12.7. RA TEST IN TN SYSTEMS
Protection against indirect contacts in TN systems must be guaranteed by means of a
protection device against overcurrents (typically MCB or fuse) which switches off the
power supply of the circuit or the electrical equipment in case of faults between an active
part and a ground mass or a protection conductor within a interval not exceeding 5s,
sufficient for the equipments.
Parts of the system to be checked
The test must be performed at the point in which the minimum short-circuit current is
possible, normally immediately downstream of the protection device to be checked.
The test must be performed between phase and PE (Z
L-PE
) and between phase and
neutral (Z
L-N
) in three-phase systems or single-phase systems.
Allowable values
The measurement is aimed at ensuring that, in every point of the system, the following
relationships are satisfied:
Z
L-PE
≤ Z
LIM
(1)
Z
L-N
≤ Z
LIM
(2)
where:
Z
L-PE
= Impedance measured between phase and PE
Z
L-N
= Impedance measured between phase and neutral
Z
LIM
=
Maximum limit impedance depending on type (MCB or Fuse) and tripping time
of the selected protection (values depending on countries)
The following selections (*) are available on the instrument:
➢
MCB curve B
→
3A, 6A, 10A, 13A, 15A, 16A, 20A, 25A, 32A, 40A, 45A, 50A, 63A,
80A,100A,125A,160A,200A
➢
MCB curve C
→
0.5A, 1A, 1.6A, 2A, 3A, 4A, 6A, 10A, 13A, 15A, 16A, 20A, 25A, 32A,
40A, 50A, 63A, 80A,100A,125A,160A,200A
➢
MCB curve D, K
→
0.5A, 1A, 1.6A, 2A, 3A, 4A, 6A, 10A, 13A, 15A, 16A, 20A, 25A,
32A, 40A, 45A, 50A, 63A, 80A,100A,125A,160A,200A
➢
Fuse gG
→
2A, 4A, 6A, 8A, 10A, 12A, 13A, 16A, 20A, 25A, 32A, 35A, 40A, 50A, 63A,
80A, 100A, 125A,160A, 200A, 250A, 315A, 400A, 500A, 630A, 800A, 1000A, 1250A
➢
Fuse aM
→
2A, 4A, 6A, 10A, 12A, 16A, 20A, 25A, 32A, 35A, 40A, 50A, 63A, 80A,
100A, 125A,160A, 200A, 250A, 315A, 400A, 500A, 630A
➢
Time of fault extinction by the protection selectable among:
0.1s, 0.2s, 0.4s, 1s, 5s
(*) The values could be subject to variations
