What Servers and Your Clothes Dryer Have in Common

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With prices for many everyday goods on the rise, small and midsize businesses are always looking for ways to cut costs and increase their return on investment (ROI). Even if "going green" hasn't earned a spot on the IT staff's priority list, there's an easy solution to cutting power and cooling costs -- and it's no further away than the electrical outlets in your server room.

If every server were in a house, 120 volts would make sense for every server. We are a 120-volt society. Since electrical codes in the United States require habitable space to be wired with 120V, 120V outlets are the primary power source in small office buildings as well. To accommodate their customers, technology vendors ship entry-level and midrange servers with a 120V power cord as standard equipment.

Since 120V is the standard, one might assume the servers would operate most efficiently at this voltage. But most servers are designed to accept both 120V and 208V. Most even have auto-sensing input circuitry that automatically adjusts to the applied input voltage.

While 120V power may be convenient, there are fundamental limitations to the equipment it can support. The majority of wall receptacles are rated at 15Amps (15A), and since Underwriters laboratory (UL) specifies that a single piece of electrical equipment is not permitted to draw more than 80% of the receptacle's rating, this limits the power supply to 12 Amps for a 15A circuit. This limitation restricts the power supply system and efficiency of the environment.

Benefits of 208V

There's a good reason that heavy-duty household appliances run on 208 to 220 volts. Remember this equation from your high school physics?

P (watts) = I (amps) x E (volts)

In other words, to produce the same wattage for a server rack, operating at higher voltage means you draw less current from the power supply so more energy will get to the server instead of being dissipated in the wires. That saves energy and reduces strain on the hardware.

Because 208V produces less current and allows more power to enter the server, running servers at 208V vs. 120V will have an impact on your ability to output power, convert power efficiently, operate your thermal power supply and improve the reliability of the general power supply. Since the most common ratings for 208V wall receptacles are 20A and 30A, the receptacles can support 300 watts and 5400 watts of power supply output in a server.

Running equipment at 208V is the superior choice even for SMBs. Although the convenience of using 120V may seem desirable, running at a higher current draw enables energy efficiency and ultimately extensive cost savings. The initial investment is small and the ROI is astounding. That's definitely something to take to management.

Once an IT manager recognizes that 208V is an option, the next step is to call in an electrician in to rewire the office space to support 208V in selected locations. Moving to 208V eliminates the need to purchase a transformer to step down load of high capacity equipment to 120V which not only saves money, but also space in the server rack. Existing servers with 120V can easily be upgraded to 208V just by purchasing an inexpensive power cord.

This story, "What Servers and Your Clothes Dryer Have in Common" was originally published by Network World.

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