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Installation Instructions
16
Signal Reference Grid
If the unit is used to supply power to a computer room or area that is equipped with a signal reference
grid or a grounded raised-floor stringer system, a grounding conductor should be connected from the
system ground bus to the grid or floor system. This conductor should be stranded or braided #8 AWG
or larger, and as short as practical. Less than 3 ft. (1m) is recommended.
1.3.4 Grounding Electrode Conductor for FPCs With Transformer
Required by code - The Liebert FPC with transformer must be grounded according to the safety
practices of NEC 250-26. A local grounding electrode conductor is recommended in addition to the
equipment safety ground which is normally run with the input power conductors. (See Figures 5
through 8.)
As shown in Figure 12, the grounding electrode conductor is run from the unit to the nearest effec-
tively grounded location (listed in order of preference):
• Building steel
• Metal water pipe
• Other made grounding electrode
The grounding electrode conductor’s size is based on the secondary circuit conductors. Table 10
shows the minimum recommended grounding electrode conductor according to the NEC
(Table 250-66).
Recommended methods for running the grounding electrode conductor (arranged by preference for
system performance; as acceptable by local and other applicable codes):
• Outside of conduit (where not subject to damage)
• Inside non-metallic conduit
• Inside non-ferrous conduit
• Inside ferrous conduit, bonded to the ferrous conduit at both ends, as acceptable by local and other
applicable codes
Table 10 Minimum grounding electrode conductor size (AWG)
kVA
Output Voltage
208V 380V 415V
15 8 8 8
30 8 8 8
50 4 8 8
75 2 6 6
100 0 4 4
125 0 2 2
150 00 2 2
200 00 0 0
225 00 0 0
300 00 0 0
AWG wire size based on 75°C copper conductors