Attachment 3 - Basic Guidance - 208V Power Distribution White Paper.pdf

Basic Guidance: 208V Power Distribution White Paper

VA standards for power distribution in telecommunications spaces specify the use of 3-phase 208V power at the IT equipment enclosure.

All modern IT equipment is equipped with auto-ranging power supply units (PSUs) that allow a range of voltage inputs, typically from 100V to 240V. This equipment functions more efficiently at higher voltages.

There is a 1 to 2 percent improvement in power supply efficiency when using 208V distribution over 120V distribution. In order to supply the same number of Watts to a server, a 120V circuit has to push more amperage than a 208V circuit. The more current carried, the more resistive heat generated, and the harder the server fans and overall data center cooling systems have to work. Less power is consumed when using the higher voltage.

The Solution Delivery (SD) Data Center & Infrastructure Engineering team has developed this guidance as a supplementary narrative to the OIT Design Guide Templates in order to provide additional detail for field OIT and FMS staff, A/Es, and implementing contractors and VA staff. Please contact the Data Center & Infrastructure Engineering team for additional detail as necessary.

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Unless otherwise specified, some servers and switches are shipped with 120V power cords.

Using IEC-60320 208V power cords (“couplers”) allows us to use the 208V banks in the standard 3-phase Rack PDUs specified in the Infrastructure Standard for Telecommunications Spaces, and to deliver up to either 15A (C13-Type E) or 20A (C19-Type I) to the IT equipment at the higher voltage. Specification of the IEC-60320 power cord option when ordering active equipment is necessary. (Note: The C13-Type E power cord is typically referred to as a C13-C14 power cord by retailers.)

The standard 3-phase Rack PDUs required for IT equipment enclosures in the data center and in Telecommunications Rooms (TRs) have Type F and Type J outlets (receptacles) typically grouped into three banks.

Each bank is provided from a different pair of the single-phase 120V phases. These may be grouped together, color-coded, or both.

The use of the 3-phase distribution equipment also simplifies power management within the telecommunications space, as phase balancing can be accomplished simply by relocating a power cord from one bank to another.

Practically speaking, 208V distribution requires the use of 3-pole circuit breakers on 120/208V circuit breaker panelboards, and circuits with 5 wires (A phase, B phase, C phase, neutral, and ground, or L+L+L+N+G). The power distribution equipment connected to these circuits – typically a Rack PDU – then supplies 208V power as the difference between the voltages on any pair of the phase wiring (A & B, B & C, or C & A). (Phases A, B, and C may also be called lines 1, 2, and 3, or L1, L2 ,and L3.)

Where the voltage on each individual phase or line varies between 0 and 120 volts, following a sine wave that repeats 60 times each second (60Hz), the resultant of combining two of these phases gives us a sine wave with a voltage that varies between 0 and 208 volts. This is shown graphically below.

References:

VA OIT Infrastructure Standards for Telecommunications Spaces:

https://www.cfm.va.gov/til/dguide/OIT-InfrastrucStdsTelecommSpaces.pdf VA OIT Design Guide Templates:

https://www.cfm.va.gov/til/dGuide/OIT-DGTemplates-CriticalTelecommSpaces.pdf

-240 -210 -180 -150 -120

-90 -60 -30

0 90 180 270 360 450 540 630 720

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208V Power from (2) 120V 60Hz phases

Phase A Phase B 208V Resultant https://www.cfm.va.gov/til/dguide/OIT-InfrastrucStdsTelecommSpaces.pdf https://www.cfm.va.gov/til/dGuide/OIT-DGTemplates-CriticalTelecommSpaces.pdf