Vertiv Liebert STS2/PDU - Figure 3 Typical One-Line Diagram of Two Pdus and a Liebert STS2

Vertiv™ | Liebert
®
STS2
™
100-1000A, 50/60Hz User Manual | Rev. 12 | 11/2017 11
4-Wire-Plus-Ground Systems — When 4-wire-plus-ground input feeds are utilized, the input power sources
must be properly grounded. Because the neutral is not switched by the Liebert STS2, the neutrals of the two
power sources are solidly interconnected. The NEC prohibits grounding a power source at more than one point.
Connecting the neutrals of two grounded power sources together effectively grounds each of the sources at
more than one point, which allows neutral current to flow on the ground system, defeats ground fault protection,
creates a safety hazard, and violates the NEC.
Where possible, the two power sources should be located in close proximity and a single neutral-to-ground bond
made (as shown in Figure 3 or as is typical with a double-ended substation).
Figure 3 Typical one-line diagram of two PDUs and a Liebert STS2
K1 K3K2 K3
K2K1
CB1
CB2
STS1 STS2
CB4 CB5CB3
225 A 225A 225 A 225A 225A 225A
Source 1 Source 2
MICB1
MICB2
Isolation
Transformer
Isolation
Transformer