13-08-2013, 04:15 PM
Basics of EMI and EMC
Basics of EMI .pdf (Size: 626.19 KB / Downloads: 122)
Introduction
Earthing, equipotential bonding and earthing are a major part of all new buildings and
facilities. These have a great influence on the EMC of the system and the mitigation of EMI
wherever applicable.
As the number of electronic devices increases, every building owner is required to abide by
all applicable EMC regulations and laws. In regards to telecommunications equipment and
cabling systems, there is often an uncertainty about what to do and to find the correct way
for a proper installation.
This guide is intended to give some basic explanation of these issues as they relate to
cabling systems. In general EMC is a vast subject and there are various books and literature
available.
This guide briefly highlights the parts covering earthing, equipotential bonding and electrical
power distribution. But all parts are important in regards to EMC and are valid for shielded
and unshielded cabling systems.
There is often a misunderstanding between the requirements for earthing and equipotential
bonding for both shielded and unshielded systems.
Save the life of humans and animals in case of any electrical fault.
This can be achieved by installing a low impedance connection to the protective conductor.
At the other end of this conductor there is a connection to an electrode in the ground.
The main connection to ground is called the protective earth (PE) and is recognised by the
typical green/yellow insulation colour.
A second function is to have a defined path for surges in the power system, lightning and
emissions from outside sources like radar station, broadcast stations etc. It is fundamental to
understand, that only a proper earthing system can prevent harm from the issues referred to
above. The intention of European standard EN 50310 is to provide the optimum earthing and
equipotential bonding conditions for buildings. Even though the focus of this discussion is for
buildings with communication technology installation, the standard shall be applied for at
least all new buildings and if possible for existing buildings.
Equipotential bonding
This refers to the need to connect all metalwork or conducting parts within an electrical panel
or on a machine to the protective earth. Equipotential bonding has a safety and an EMC
aspect. This is also the case in a house or commercial building, where ideally all metallic
components are connected to the equipotential bonding network. These include:
• All metal conduits within the building, e.g. water and gas conduits
• All metal parts of the building or the construction
o steel girder
o Metal Facade
o Steel in cement
• Metal cabinets for data or power distribution
• Raised floors with metal uprights
• Metal cable conduit
Installation of IT cabling systems
As any building today contains IT equipment, electrical and other standards reflect this in
their content.
This means that all rules and recommendations in regards to EMC and safety apply to any
kind of IT system. From a practical point of view, the most common equipment includes
racks and metal panels, metal path ways, raised floors with metal frames.
In regards to safety and EMC all equipment needs a defined path to EB (equipotential
bonding).
Conclusion
The efforts and cost for a well designed eathing and bonding system is independent of the
kind of media that is installed. This is recognised by EN 50310 and EN 50174-2.
The illusion to save money or avoid trouble by installation of fibre optic cables or UTP cables
is an old fairy tale. All standards state this clearly in their publications. Fibre connections
shall be installed between buildings. This is applicable for large installations and plants.
With respect to 10 Gigabit Ethernet, the combination of a shielded system and a well
designed EB system provides maximum EMC performance of the building. The ANEXT and
background noise issues emphasise this.