EMC behaviour of different electrical distribution architecturing
The system earthing arrangement must be properly selected to ensure the safety of life and property. The behaviour of the different systems with respect to EMC considerations must be taken into account. Figure R1 below presents a summary of their main characteristics.
European standards (see EN 50174-2, EN 50310 and HD 60364-4-444) recommend the TN-S eathing system which causes the fewest EMC problems for installations comprising information-technology equipment (including telecom equipment).
|Safety of persons||Correct
Use of residual current devices (circuit breaker)is mandatory
Continuity of the PE conductor must be ensured throughout the installation
|Safety of property||Correct||Poor||Correct||Poor|
|Medium ground-fault current (< about ten amps)||High ground-fault current (about 1 kA)||Low ground-fault current for first fault (< about ten mA), but high for second fault||High ground-fault current (about 1 kA)|
|Availability of energy||Correct||Correct||Excellent||Correct|
||Poor (to be avoided)
||Poor (not recommended)
When an installation includes high-power equipment (motors, air-conditioning, lifts, power electronics, etc.), it is advised to install one or more transformers specifically for these systems. Electrical distribution must be organised in a star system and all outgoing circuits must exit the main low-voltage switchboard (MLVS).
Electronic systems (control/monitoring, regulation, measurement instruments, etc.) must be supplied by a dedicated transformer in a TN-S system.
Figure R2 below illustrates these recommendations.