Phase Imbalance
All systems are provided with 2 bulk power assemblies (BPAs), with separate line cords. Each BPA uses
only 2 phases of a 3-phase power system, causing phase imbalance. Single-phase systems use either two
phases of a 3-phase power system, or one phase and neutral. Phase currents will be divided between 2
line cords in normal operation.
The Eserver pSeries 670 has one bulk power regulator (BPR) per BPA, with its Phase A and Phase B (or
neutral) Line Currents determined by Power/Vline, and a Phase C Line Current of 0.
Note: Power is calculated from “Total System Power Consumption” on page 140. Vline is line-to-line
nominal input voltage.
Balancing Power Panel Loads (3-Phase Systems)
The Eserver pSeries 670 requires three-phase power. Two of three phases will carry an equal amount of
current, with no current drawn on the third phase. The following figure is an example of feeding several
loads of this type from two power panels in a way that balances the load among the three phases.
Note: Use of ground-fault-interrupt (GFI) circuit breakers is not recommended for this system because
GFI circuit breakers are earth-leakage-current sensing circuit breakers and this system is a high
earth-leakage-current product.
The method illustrated in the preceding figure requires that the connection from the three poles of each
breaker to the three phase pins of a connector be varied. Some electricians may prefer to maintain a
consistent wiring sequence from the breakers to the connectors. The following figure shows a way to
balance the load without changing the wiring on the output of any breakers. The three-pole breakers are
alternated with single-pole breakers, so that the three-pole breakers do not all begin on Phase A.
Chapter 2. Physical Characteristics of Systems 129
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