Liebert NX User Manual page 27

NOTE
Both the rectifier and bypass feeds must come from the same utility source. The UPS can be
powered from separate sources provided all the following conditions are met:
1. The transformers are delta/wye isolation transformers where the wye secondary's are
connected to the NX 480V UPS.
2. The individual transformer used to supply the Bypass of the NX 480V is solidly bonded to
earth ground at the transformer.
3. The individual transformer used to supply the Input (rectifier) of the NX 480V is solidly
bonded to earth ground at the transformer.
4. There are no appreciable ground currents flowing between the two transformers.
5. No delta/delta (ungrounded or corner grounded) transformers are used as a source to the
NX 480V UPS.
6. No high resistance or low resistance grounds can be used in the neutral bonding path to
ground of the delta/wye isolation transformers described above in Items 2 and 3.
7. All applicable NEC standards and wiring rules are enforced.
8. The internal bypass to input (rectifier) shorting bars in the NX 480V UPS are removed.
The above all apply to single-module systems.
9. For 1+N paralleled system, the Bypass to each unit must be fed from the same utility
source.
Output System Connections—Ensure Correct Phase Rotation
10. Connect the system output cables between the UPS output busbars (A-B-C terminals) and the
critical load and tighten the connections to 88 lb-in. (10 N-m) (M8 bolt).
WARNING
!
Risk of electric shock. Can cause injury and death.
If the load equipment will not be ready to accept power on the arrival of the commissioning
engineer, then ensure that the system output cables are safely isolated.
Observe the battery cable polarity. Be sure that the battery connector is made with the
correct polarity.
11. Refit all protective covers removed for cable installation.
Frequency Converter Mode
If a frequency converter configuration is used, connect the AC input supply cables to the rectifier
input busbars (A-B-C terminals). Torque to 88 lb-in (10N-m) for M8 bolts. Ensure correct phase
rotation. There will not be any AC bypass supply cables to the bypass input (A-B-C terminals) and
tighten the connections.
NOTE
The operations described in this section must be performed by authorized electricians or
qualified technical personnel. If any difficulties arise, contact Liebert at 1-800-LIEBERT.
NOTE
For frequency converter operation, ensure that the linking busbars between the bypass and the
rectifier input are removed.
® ™
Liebert NX 17
Electrical Connections