Equipotential Bonding - Siemens SIMATIC S5-90U System Manual

S5-90U/S5-95U
3.5.3

Equipotential Bonding

Potential differences may occur between separate sections of the system if
• Programmable controllers and I/Os are connected via non-floating interface modules or
• Cables are shielded at both ends but grounded via different sections of the system.
Potential differences may be caused, for instance, by differences in the system input voltage. These
differences must be reduced by means of equipotential bonding conductors to ensure proper
functioning of the electronic components installed.
Note the following for equipotential bonding:
• A low impedance of the equipotential bonding conductor makes equipotential bonding more
efficient.
• If any shielded signal cables connected to earth/protective earth at both ends are laid between
the system sections concerned, the impedance of the additional equipotential bonding conductor
must not exceed 10 % of the shield impedance.
• The cross-section of the equipotential bonding conductor must be matched to the maximum
compensating currents. The following cross-sections are recommendable:
- 16 mm copper wire for equipotential bonding line up to 200 m (656.2 ft).
2
- 25 mm copper wire for equipotential bonding line over 200 m (656.2 ft).
2
• Use equipotential bonding conductors made of copper or zinc-plated steel. Equipotential bonding
conductors are to be connected to earth/protective earth via a large contact area and to be
protected against corrosion.
• The equipotential bonding conductor should be laid in such a way as to achieve a relatively
small contact area between equipotential bonding conductor and signal cables (see Figure 3-31).
Figure 3-31. Laying Equipotential Bonding Conductor and Signal Cable
EWA 4NEB 812 6115-02b
signal cable
equipotential bonding conductor
Installation Guidelines
3-35