View source for System earthing arrangements for installations comprising UPSs

{{Menu_Characteristics_of_particular_sources_and_loads}}__TOC__
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 {{FigRef|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.

{{tb-start|id=Tab1363|num=N23|title=Main characteristics of system earthing arrangements|cols=5}}
{| class="wikitable"
|-
! Type of arrangement 
! IT system 
! TT system 
! TN system
|-
| '''Operation''' 
| 
*Signaling of first insulation fault 
*Locating and elimination of first fault 
*Disconnection for second insulation fault
| 
*Disconnection for first insulation fault
| 
*Disconnection for first insulation fault
|-
| '''Techniques for protection of persons '''
| 
*Interconnection and earthing of conductive parts 
*Surveillance of first fault using an insulation monitoring device (IMD) 
*Second fault results in circuit interruption(circuit-breaker or fuse)
| 
*Earthing of conductive parts combined with use of RCDs 
*First insulation fault results in interruption by detecting leakage currents
| 
*Interconnection and earthing of conductive parts and neutral imperative 
*First insulation fault results in interruption by detecting overcurrents (circuit-breaker or fuse)
|-
| '''Advantages and disadvantages''' 
| 
*Solution offering the best continuity of service (first fault is signalled) 
*Requires competent surveillance personnel (location of first fault)
| 
*Easiest solution in terms of design and installation 
*No insulation monitoring device (IMD) required 
*However, each fault results in interruption of the concerned circuit
| 
*Low-cost solution in terms of installation 
*Difficult design (calculation of loop impedances) 
*Qualified operating personnel required 
*Flow of high fault currents
|}

== Essential points to be checked for UPSs  ==

{{FigureRef|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

{{FigImage|DB422659_EN|svg|N24|The essential points that must be connected in system earthing arrangements}}