Configuring Your Neutral and Ground Connections
6.1Preferred Grounding Configuration, Wye-Connected Service
The most common configuration of Series 610 UPS Multi-Module Systems is with 480 VAC input, 480 VAC output and a connected load consisting of multiple Power Distribution Units (PDUs) with isolation transformers in the PDUs to produce 208 VAC. For Canadian customers, the UPS modules usually have 600 VAC input and output. The same principles apply if the connected load is an isola- tion transformer feeding various loads. Figure 4 shows a typical installation. The Maintenance Bypass Switchgear is shown separately for clarity, but may be contained within the System Control Cabinet (SCC)/switchgear.
Notice that the UPS module input and the system bypass input are connected to a grounded-wye ser- vice. In this configuration, the UPS module is not considered a separately derived source.
All of the UPS module output neutrals are solidly connected to the SCC neutral. A parity-sized neu- tral is recommended between the UPS module and the SCC for best system performance. The SCC neutral is solidly connected to the building service neutral, which is bonded to the grounding conduc- tor at the service entrance equipment.
The isolation transformers in the PDUs are considered a separately derived source. Therefore the PDU neutral should be bonded to the PDU grounding conductor and connected to a local grounding electrode in compliance with NEC 250-26. (PDUs are connected to the critical load output of the SCC, but are not shown in Figure 4 for clarity.)
Figure 4 Preferred grounding configuration, wye-connected service
Impedance-grounded wye sources require an Isolated Neutral Kit in addition to the grounding and neutral conductors shown above—see 6.5 - Grounding Configuration, Corner- Grounded Delta or Impedance-Grounded Wye.
NOTE
If there is a 4-pole Automatic Transfer Switch (ATS) between the service entrance and the UPS, this configuration cannot be used. Refer to 6.2 - Alternate Grounding Configuration, Wye- Connected Service or 6.3 - Preferred Grounding Configuration With Isolated Bypass to determine a suitable configuration.
