User`s guide

Eaton
®
User's Guide for Basic, Monitored, and Switched ePDUt S 164202115 Rev 1
11
Chapter 4 Three-Phase Load Balancing
This chapter explains the relationship between input and output load currents in a
three‐phase Monitored ePDU . This information applies to any three‐phase Monitored
ePDU. See Figure 5 for an example of a 30A three-phase system.
Display
L21 - 30P
30A/208V Three-Phase
Figure 5. 30A Three-Phase System Example
The three-phase input voltage is 208V phase-to-phase and 120V phase-to-neutral.
Figure 5 shows two types of outlets:
S IEC 320-C13 outlets. These outlets are connected across phase-to-phase and provide
208V to the supplied equipment.
S NEMA 5-15 outlets. These outlets are connected phase-to-neutral and provide 120V
to the supplied equipment.
C A U T I O N
S The current limit values defined for the ePDU output circuits should be observed (13.9A shown in
Figure 5) to prevent input overload. The input load current limits for the supply must be observed to
prevent the risk of overload to the supply circuit breaker (4, 5, and 6, with a 24A limit shown in Figure 5).
S Failure to observe these limits may cause loss of power because the circuit breaker will open when
overloaded.
The output branch circuits are protected by a 20A rated branch circuit breaker (UL489)
in line with the National Electrical Code
®
(NEC
®
) requirements and the maximum
design load of each output circuit (if not limited by other factors) would be 16A
(80% rated).
If the applied load uses the IEC 320-C13 outlets, each input phase wire is connected
to two output circuits (as shown in Figure 5). The value of the input phase current is
therefore the sum of the two output circuit currents. However, the value is not a
simple sum because the load currents of the two output circuits are not in phase with
each other. The sum of the current is a function of three-phase electrical circuits,
where the input phase current is 1.73
the output current. For example, 1A on each
output circuit results in 1.73A on each input phase.