System earthing arrangements for installations comprising UPSs
Application of protection systems, stipulated by the standards, in installations comprising a UPS, requires a number of precautions for the following reasons:
- The UPS plays two roles
- A load for the upstream system
- A power source for downstream system
- When the battery is not installed in a cabinet, an insulation fault on the DC system can lead to the flow of a residual DC component
This component can disturb the operation of certain protection devices, notably RCDs used for the protection of persons.
Protection against direct contact
(see Fig. N23)
All installations satisfy the applicable requirements because the equipment is housed in cabinets providing a degree of protection IP 20. This is true even for the battery when it is housed in a cabinet.
When batteries are not installed in a cabinet, i.e. generally in a special room, the measures presented at the end of this chapter should be implemented.
Note: The TN system (version TN-S or TN-C) is the most commonly recommended system for the supply of computer systems.
|Type of arrangement||IT system||TT system||TN system|
|Techniques for protection of persons||
|Advantages and disadvantages||
Essential points to be checked for UPSs
Figure N24 shows all the essential points that must be interconnected as well as the devices to be installed (transformers, RCDs, etc.) to ensure installation conformity with safety standards