points why ups required separate earth pit UPS input particularly converter section always consists of iii phases only. The UPS static bypass switch also consists only iii phases. The service switch comprises iii phases + neutral of the system which will be brought forward to the load distribution board. As an international standard practice, the neutral is always brought via the knife switch and the rest 3 phases via a breaker or dis connector. Also, at output of the service switch, the neutral is connected via knife switch. This is so that there shall be continuity of the neutral. As far as UPS Inverter section is concerned either isolated or non-isolated type, the inverter section is always built with 3 phase output only. Particularly with PWM technology, it is very hard to design the 4 wire system. Hence, UPS output always consists 3 phases only. The Inverter accepts the unbalanced load i.e. difference in phase currents without the floating neutral. The technology accepts the different in leg currents of the inverter. To cater for the phase to neutral voltage, UPS takes as reference of the system neutral. The neutral must be earthed i.e. the system neutral and the UPS neutral are being brought at the same level. This is the correct meaning of the UPS to be earthed. Theoretically, UPS need not be earthed but practically the system neutral shall be referenced. Depending upon the UPS configuration one has to consider for merging of the system neutral. SN Earthing Noida