How to ground the UPS battery cabinet

Essentially, the UPS enclosure must be connected to ground through the building's grounding-electrode system by way of a grounding electrode conductor. This connection in an ungrounded system serves as the grounding reference point for all conductive equipment in the ungrounded system that does not carry current under normal conditions.

Without a properly installed grounding system, your UPS won't function correctly. A grounding system allows circuit protection to clear a ground fault, and provides paths for diverting surge current away from the UPS and for removing undesirable currents from the critical load. So what can you do to ensure your grounding system allows your UPS

The cabinet grounds are inherently connected to the UPS ground bus via the metal chassis. You must connect the supporting racks of a wet-cell installation to the battery disconnect and to the UPS module ground bus. You should connect the racks directly to the local UPS room ground bus only if required by local electrical codes.

It is important to note that even though the UPS enclosure and downstream equipment may still be effectively bonded to the supply-source enclosure in this condition, the system is not considered grounded unless a current-carrying conductor is connected to ground.

Typically, the grounding point is a copper bar mounted on insulators in the electrical room and bonded to the local building steelwork. Whenever you use a delta-connected supply for a UPS system, you must create an artificial neutral. In such cases, a three-resistor network typically provides a logic reference point for the bypass input.

Bond the neutral of the UPS output to the local UPS room ground bus. Some UPS modules come equipped with an input isolation transformer, but these don't influence whether you deem the system to be a separately derived source.