Liebert 600TTM installation manual Grounding Configuration with Ungrounded Delta Source Input

7.2Grounding Configuration, 480 or 600 VAC Input and Output, Delta Source

Figure 4 Grounding Configuration with Ungrounded Delta Source Input

As previously mentioned, Series 600T UPS systems require a bypass input netrual for sensing and monitoring. With a wye-connected input source, the installer should always connect the building service neutral to the System Control Cabinet (SCC) output neutral to achieve this. When the building service is delta-connected, however, the installer must take special steps to ensure reliable UPS functioning.

If building service is ungrounded delta (and there is no intent to operate with one corner of the delta grounded, either on purpose or accidentally), the SCC requires the Series 600T Artificial Neutral Kit for proper operation. This kit uses a resistor network to create a reference point for the bypass input. In this case, the SCC output neutral must be bonded to the SCC ground.

If the building service is corner-grounded delta or an Impedance-grounded wye, the SCC requires the Isolated Neutral Kit. This kit uses control isolation transformers to create a reference point. For this application, the SCC output neutral must not be bonded to the SCC ground.

NOTE

The Artificial Neutral Kit introduces a maximum current of 0.3 amps to ground. Take care to ensure that this does not interfere with the operation of any upstream ground-fault detection devices.

16 Configuring Your Neutral and Ground Connections