HP ProLiant BL660c ISS Technology Update, Volume 8, Number 3 - Page 4

ISS Technology Update, Volume 8, Number 3, Calculating 3-phase input power

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ISS Technology Update Figure 2-1. Physically mapping 3-phase power to c7000 AC input module. Volume 8, Number 3 Calculating 3-phase input power Figure 2-2 shows how the power is electrically mapped for both North America and International 3-phase power into the singlephase power supplies. International 3-phase power uses five conductors, including a true neutral conductor, allowing each of individual phases to deliver the full 230 volts. North American 3-phase power uses four conductors. The neutral conductor for one phase is one of the line conductors for another phase. Thus, only a differential voltage and not the full 208 volts is delivered to each of the power supplies. Additionally, North American standards state that circuits should not continuously draw more than 80% of their rated current. Therefore, a 30 Amp circuit delivers only 24 Amps continuously. All of this must be taken into consideration when calculating the total input power from 3-phase circuits. For a 30 Amp, 3-phase North American circuit, the input power delivered is calculated as follows: Continuous power = 1.732 x 208V x (.8 x 30A) = 8.6 kVA For a 16 Amp 3-phase International circuit, this would be the input power delivered: Continuous power = 3 x 230V x 16A = 11.1 kVA 4

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ISS Technology Update
Volume 8, Number 3
4
Figure 2-1. Physically mapping 3-phase power to c7000 AC input module.
Calculating 3-phase input power
Figure 2-2 shows how the power is electrically mapped for both North America and International 3-phase power into the single-
phase power supplies.
International 3-phase power uses five conductors, including a true neutral conductor, allowing each of individual phases to
deliver the full 230 volts. North American 3-phase power uses four conductors. The neutral conductor for one phase is one of
the line conductors for another phase. Thus, only a differential voltage and not the full 208 volts is delivered to each of the
power supplies. Additionally, North American standards state that circuits should not continuously draw more than 80% of their
rated current. Therefore, a 30 Amp circuit delivers only 24 Amps continuously. All of this must be taken into consideration when
calculating the total input power from 3-phase circuits.
For a 30 Amp, 3-phase North American circuit, the input power delivered is calculated as follows:
Continuous power = 1.732 x 208V x (.8 x 30A) = 8.6 kVA
For a 16 Amp 3-phase International circuit, this would be the input power delivered:
Continuous power = 3 x 230V x 16A = 11.1 kVA