Siemens SINAMICS G130 Engineering Manual page 143

Fundamental Principles and System Description
Engineering Information
The shield of the shielded cable well bonded at both ends ensures optimum high-frequency equipotential bonding
between the converter and motor terminal box.
In older installations in which unshielded cables are already installed, or where the cables used have a shield with
poor high-frequency properties, or in installations with poor grounding systems, it is strongly recommended that an
additional equipotential bonding conductor made of finely stranded, braided copper wire with a large cross-section
2
(≥ 95 mm ) is installed between the PE busbar of the converter and the motor housing. This conductor must be
routed in parallel and as close as possible to the motor cable.
Optimized connections for high-frequencies between the motor terminal box and motor housing [3]
The electrical connection between the motor terminal box and the motor housing on some motors or motor series is
not generally designed to offer ideal high-frequency properties.
For example, flat nonconductive seals between the terminal box and housing are used on most motors with grey
cast-iron housing. This means that the electrical connection is essentially provided through a few screw points which,
even when their total effect is taken in account, do not offer an optimum, low-impedance connection for high-
frequency interference.
For this reason, the possibility of providing an additional equipotential bonding connection with good high-frequency
properties between the terminal box and motor housing must be considered. This is particularly true if the available
grounding system is poor, a problem often encountered when older installations are modernized.
2
This connection should be made with the shortest possible grounding cables with a large cross-section ( ≥ 95 mm )
and designed for low impedance over a wide frequency range. Finely stranded, braided round copper wires or finely
stranded, braided flat copper strips would be suitable for the purpose. The contact points on the terminal box and
housing must be made over the largest possible area, treated carefully to remove paint or varnish and have good
conducting properties.
The following photographs show a selection of suitable cables.
Finely stranded, braided round copper wires Finely stranded, braided flat copper strips
On motors which are constructed with a large-area, adequately conductive connection between the terminal box and
housing, no additional connection is required and can be omitted. Siemens SIMOTICS M compact asynchronous
motors in series 1PL6, 1PH7 and 1PH8 as well as SIMOTICS FD motors feature a connection of this kind as they are
specially designed for converter-fed operation.
Optimized connection for high-frequencies between motor housing, gearbox and driven machine [4], [5]
A further equipotential bonding measure is to link the motor housing to the gearbox and the driven machine in a
conductive connection with good high-frequency properties. A lead made of finely stranded, braided copper cable
2
with a large cross-section (≥ 95 mm ) should also be used for this purpose.
Optimum high-frequency bond between converter and foundation ground [6]
As a final equipotential bonding measure, the converter must be solidly bonded for high-frequency currents with the
2
foundation ground. A lead made of finely stranded, braided copper cable with a large cross-section (≥ 95 mm )
should also be used for this purpose.
SINAMICS Engineering Manual – November 2015
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Ó Siemens AG