Device Input Power; Btus Required For Cooling; Input/Inrush Current; Leakage Current - HP ProLiant BL280c - G6 Server Introduction Manual

Device input power

The amount of power a device turns into work and dissipates as heat is known as real (or true) power
and is measured in watts (W). Since any heat created by electrical equipment must be extracted,
knowing the total amount of watts dissipated by systems in a data center helps determine the cooling
capacity needed in the facility.

BTUs required for cooling

The British Thermal Unit (BTU) is the standard for measuring the capacity of cooling systems. The
amount of power (watts) consumed by equipment determines the number of BTUs/hr required for
component cooling, based on this formula:
BTUs/hr = watts x 3.41.
For example: 399 watts x 3.41 = 1360 BTUs/hr
Air conditioning equipment is typically rated in terms of tons of cooling, an old measurement based
on the cooling ability of tons of ice (1 ton of cooling = 12000 BTUs/hr).

Input/inrush current

Input current is the amount of amperes a system draws during normal operation. However, when AC
voltage is first applied (power cord is plugged in and/or a circuit breaker is switched on), power
supplies of electrical components can momentarily draw several times more current than they will
draw while operating. This inrush current is cumulative across devices within a common power circuit,
and it must be considered when building a rack. Power supplies in HP servers include circuitry that
minimizes inrush current. Staggering activation of segmented circuits can further reduce the effects of
inrush current.

Leakage current

Leakage current (typically measured in milliamps) is residual current that originates in power supply
filters and flows from chassis ground to the phase and neutral power conductors. Leakage current is
cumulative across components within a power distribution circuit and can become a hazard if proper
grounding procedures are not used
.

Determining power needs and achieving power efficiency

Power supplies for ProLiant servers include a chassis nameplate that typically includes the following
information:
• Input requirement—the AC input voltages (or ranges) and associated maximum current draw
• Output power—the DC voltage, maximum current (amperage), and maximum power (wattage)
Nameplate ratings, therefore, define the input requirements of a power supply operating at full
power. Since power supplies rarely operate at their rated capacity, using nameplate ratings for
estimating system power requirements could yield inflated numbers that result in excessive power
infrastructure costs.
Figure 1 illustrates how the use of nameplate ratings can distort power distribution planning. The
ProLiant DL380 G6 implements the HP Common Slot Power Supply bay. This bay design, used across
several ProLiant platforms, can accommodate 460W, 750W, and 1200W power supplies.
Factory configurations of the DL380 G6 include models equipped with 460W and 750W, and
customers can build or specify custom configurations. Customers building a system with custom-
configured DL380 G6 servers might choose the 750W power supply to ensure headroom for server
needs and use the associated nameplate ratings as a guide for power distribution needs. This
approach yields nameplate ratings-based figures that will likely be unrealistically high. As indicated in
3