Siemens Sivacon S8 Planning Information page 99

Dimensioning of protective conductors
According to IEC 61439-1, section 8.4 and 8.8, an earth
continuity connection (PE, PEN) must be ensured, which
must meet the following requirements in accordance with
IEC 61439-1.
• According to subsection 8.4.3.2.2:
"All exposed conductive parts of the assembly shall be
interconnected together and to the protective conductor
of the supply or via an earthing conductor to the earthing
arrangement. These interconnections may be achieved
either by metal screwed connections, welding or other
conductive connections or by a separate protective
conductor." Tab. 10/1 must be used for a separate pro-
tective conductor.
Furthermore, certain exposed conductive parts of the
assembly which do not constitute a danger need not be
connected to the protective conductor.
This applies
– "either because they cannot be touched on large
surfaces or grasped with the hand
– or because they are of small size (approximately 50 mm
by 50 mm) or so located as to exclude any contact with
live parts."
"This applies to screws, rivets and nameplates. It also
applies to electromagnets of contactors or relays,
magnetic cores of transformers, certain parts of releases,
or similar, irrespective of their size. When removable parts
are equipped with a metal supporting surface, these
surfaces shall be considered sufficient for ensuring earth
continuity of protective circuits provided that the pressure
exerted on them is sufficiently high."
Tab. 10/1: Cross-sectional areas of protective conductors made of
copper according to subsection 8.4.3.2.2 of IEC 61439-1
Rated operating current I
I ≤ 20
e
20 < I
≤ 25
e
25 < I ≤ 32
e
32 < I ≤ 63
e
63 < I
e
1)
S = cross section of phase conductor in mm
96 SIVACON S8 Planning Principles – Technical annex
Minimum cross section of
e
protective conductor
1)
S
2
2.5 mm
2
4 mm
2
6 mm
2
10 mm
2
• According to subsection 8.4.3.2.3:
"A protective conductor within the assembly shall be so
designed that it is capable of withstanding the highest
thermal and dynamic stresses arising from faults in
external circuits at the place of installation that are
supplied through the assembly. Conductive structural
parts may be used as a protective conductor or a part of
it." The following is required for PEN conductors in
addition:
- Minimum cross section ≥ 10 mm
- PEN cross section > N cross section
- "Structural parts shall not be used as PEN conductors.
However, mounting rails made of copper or aluminium
may be used as PEN conductors."
- If the PEN current can reach high values (e.g. in elec-
trical installations with many fluorescent lamps), it may
be required that the PEN conductor has the same or a
higher current carrying capacity as / than the phase
conductor. This capacity value must be agreed separately
between the assembly manufacturer and the user.
• According to section 8.8 (for terminals of protective
conductors led into the assembly from the outside):
In the absence of a special agreement between the
assembly manufacturer and the user, terminals for pro-
tective conductors shall be rated to accommodate copper
conductors of a cross-sectional area based on the cross
section of the corresponding phase conductor
(see Tab. 10/2).
Tab. 10/2: Minimum requirements for connecting protective
copper conductors (PE and PEN) according to section 8.8 (from the
outside) of IEC 61439-1
Permissible cross-sectional
range of phase conductors S
2
S ≤ 16 mm
2 2
16 mm < S ≤ 35 mm
2 2
35 mm < S ≤ 400 mm
2 2
400 mm < S ≤ 800 mm
2
800 mm < S
1) The neutral current can be influenced by load harmonics to a significant
extent.
2 2
(Cu) or 16 mm (Al)
Minimum cross section of
corresponding protective
1)
conductor (PE, PEN) S
P
S
2
16 mm
½ x S
2
200 mm
¼ x S