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Can I use a transformer that doesn't match my high-voltage server?

The specs of the 480-V power equipment are all the same as a 400-V step-up transformer. The only difference is voltage. Can we use the 480-V transformer with 400-V servers?

If the designed power supply voltage is wrong, don't try to use it for something else. And never run any equipment...

on a voltage higher than it was designed to use.

Trying to use another type of transformer is not only dangerous, but it also violates a server's UL listing since you would not be using it for the purpose that UL tested and listed it.

There are two important parameters for a transformer: voltage and current.

Regarding the difference in transformer and server voltage, 480 Volts is a three-phase power standard used in North America. Although there has been some discussion about designing servers for 480-V power, they are not readily available.

This higher voltage distributes power to transformers that step it down to 120/208 V (120 is the phase-to-neutral voltage and 208 is the phase-to-phase voltage, either of which can be used to run servers). In rare cases, transformers are used in reverse to step up 208 Volts to 480 V. Large motors and heaters are typically the only equipment run on 480 V.

High voltage, low waste

Industry groups have advocated for 400-V European standard power, which is actually used in some U.S. data centers today. It yields higher energy efficiency and simplifies phase balance. This is accomplished with special 480 to 400 V three-phase transformers that are not commonly available. The servers still run at 230 Volts supplied power.

Primarily in Europe, 400 V is the three-phase power standard. A lower voltage can be derived from 400 V without an additional transformer, as is needed for 480 V. Depending on location, the supplied and stepped-down voltage might be 380/220, 400/230 or 415/240 -- all generally referred to as 400-Volt service. Importantly, servers run on the lower phase-to-neutral voltage of 220, 230 or 240 V, not the phase-to-phase voltage of 380, 400 or 415.

Check your ratings

The nameplate on a server is a legally required marking that gives the electrical characteristics, usually with the model and serial numbers and standards with which it complies. Your high-voltage server is probably rated at 250 Volts (and possibly also at 110, 115 or 120 V).

All modern servers should be designed to operate on input power up to 250 V. This allows the same server to operate in a U.S. data center on 120 or 208 V, or in a European 220-, 230- or 240-V service without modification.

About the author:
Robert McFarlane is a principal in charge of data center design at Shen Milsom and Wilke LLC, with more than 35 years of experience. An expert in data center power and cooling, he helped pioneer building cable design and is a corresponding member of ASHRAE TC9.9. McFarlane also teaches at Marist College's Institute for Data Center Professionals.

This was last published in March 2015

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I don't know why anyone would consider running a server on a power supply voltage that is greater than its specification, doing that is dangerous.
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