Specifications

SINAMICS G150
Drive converter cabinet units
Conductor cross-sections and connections
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Siemens D 11 · 2008
3
Overview (continued)
Required cable cross-sections for line and motor
connections
It is always advisable to use 3-wire three-phase cables or to con-
nect several cables of this type in parallel. There are two main
reasons for this:
• This is the only method by which the high IP55 degree of pro-
tection or better can be easily achieved for the motor terminal
box because the cables are fed into the terminal box via
screwed glands and the number of possible glands is limited
by the geometry of the terminal box. Single cables are less
suitable.
• With three-phase cables, the total ampere-turns over the ca-
ble outer diameter equals zero and they can be routed in (con-
ductive, metal) cable ducts or racks without any noticeable
currents (ground current or leakage current) being induced in
these conductive, metal connections. The danger of induced
leakage currents and thus of increased cable sheath losses is
greater for single cables.
The cable cross-section required depends on the current trans-
ferred in the cable. The permissible current loading of cables is
defined, for example, in DIN VDE 0276-1000. It depends partly
on ambient conditions such as temperature and partly on the
type of routing. When laid singly, the cables are cooled relatively
well. Where there are several cables routed together, they can
heat each other up, and thus receive much poorer ventilation.
Please note the corresponding derating factors for these supple-
mentary conditions in DIN VDE 0276-1000. With an ambient
temperature of 40 °C, the cross-sections of copper cables can
be based on the following table.
Current carrying capacity in accordance with DIN VDE 0298
Part 2 at 40 °C
With higher currents, cables must be connected in parallel.
Note
: The recommendations for the North American market in
AWG or MCM must be taken from the appropriate NEC
(National Electrical Code) or CEC (Canadian Electrical Code)
standards.
G rounding
Required PE conductor cross-sections:
The PE conductor must be dimensioned taking into account the
following data:
• In the case of a ground fault caused by voltage losses of the
ground fault current on the PE conductor, no impermissible
high contact voltages may occur (< 50 V AC or < 120 V DC,
EN 50178 Section 5.3.2.2, IEC 60364-5-54).
• The PE conductor must not be excessively loaded by any
ground fault current it carries.
• If it is possible for continuous currents to flow through the PE
conductor when a fault as defined in EN 50178 Section 8.3.3.4
occurs, the PE conductor cross-section must be dimensioned
for this continuous current.
• The PE conductor cross-section must be selected in accor-
dance with 60204-1.
Note
: The recommendations for the North American market in
AWG or MCM must be taken from the appropriate NEC
(National Electrical Code) or CEC (Canadian Electrical Code)
standards.
• Switchgear and motors are usually grounded separately via a
local ground electrode. With this constellation, the ground fault
current flows via the parallel ground connections and is di-
vided. With this grounding system, no impermissible contact
voltages can occur, despite the PE conductor cross-sections
used in the above table. Based on experience with different
grounding configurations, however, we recommend that the
ground wire from the motor should be routed directly back to
the converter. For EMC reasons and to prevent bearing cur-
rents, symmetrical motor cables rather than four-wire cables
should be used here. The ground connection (PE) must be
routed separately or arranged symmetrically in the motor ca-
ble. The symmetry of the PE conductor is achieved using a
conductor surrounding all phase conductors or using a cable
with a symmetrical arrangement of the three phase conduc-
tors and three ground conductors.
• Through their high-speed control, the converters limit the load
current (motor and ground fault currents) to an rms value cor-
responding to the rated current. Because of this, we recom-
mend use of a PE conductor cross-section that is similar to the
outer conductor cross-section for grounding the control cabi-
net.
Cross-section of
3-wire cables
With single
routing
With several cables on a
common cable rack
mm
2
A A
50 138 95
70 176 121
95 212 146
120 245 169
150 282 194
185 323 222
240 380 261
300 418 289
Cross-section of
outer conductor
Minimum cross-section of external
copper PE conductors
mm
2
mm
2
Up to 16 Minimum cross-section of outer conductor
16 ... 35 16
35 and above At least half the cross-section of outer
conductor
© Siemens AG 2008