Siemens S7-400 installation manual Potential Differences, Equipotential Bonding Conductor

Assembling and Installing Systems

A.6 Equipotential Bonding

Potential Differences

Potential differences can occur between separate system components, leading to high transient currents; for example, if cable shields are fitted on both sides and grounded at different system components.

Potential differences can be caused by different electrical supplies.

!	Caution
	This can result in damage.

Cable shields are not suitable for equipotential bonding.

Use the prescribed cables exclusively (e.g. those with a 16 mm2 cross-section). Ensure also that the cable cross-section is adequate when installing MPI/DP networks, since otherwise the interface hardware may be damaged or even destroyed.

Equipotential Bonding Conductor

You must reduce the potential differences by laying equipotential bonding conductors to ensure that the electronic components used function correctly.

Observe the following points for installing an equipotential bonding conductor:

•The lower the impedance of the equipotential bonding conductor, the higher the efficiency of the equipotential bonding.

•Where two sections of an installation are interconnected via shielded signal lines whose shields are connected to the ground/protective conductor at both ends, the impedance of the additional equipotential bonding conductor must not exceed 10% of the shield impedance.

•The cross-section of an equipotential bonding conductor must be rated for the maximum circulating current. In practice, equipotential bonding conductors with a cross-section of 16 mm2 have proved to be effective.

•Use equipotential bonding conductors made of copper or zinc-plated steel. Provide a large-area contact between the cables and the ground/protective conductor and protect them from corrosion.

•Lay the equipotential bonding conductor in such a way that the surface between the conductor and the signal lines is as small as possible. (see Figure A-5).

Automation System S7-400	Hardware and Installation	A-15
A5E00850741-01