S02 - Attachment 4 - Basic Guidance - Zone PDU Power Distribution.pdf

OIT Solution Delivery Data Center & Infrastructure Engineering 8 July 2020

Basic Guidance: Zone PDU Power Distribution

VA standards for power distribution in telecommunications spaces specify the use of zone Power Distribution Units (zPDUs) at the IT equipment enclosure when busbar distribution is not utilized. This document describes why zone PDUs are specified, and why specific configurations of the devices are necessary.

What is a zone PDU? As used in VA telecommunications spaces, the zone PDU is a rack-mounted power distribution unit designed to be installed in a standard rack with EIA/TIA 19” wide rails. The zone PDU has multiple A/B redundant inputs and multiple A/B redundant outputs. It provides standardized power distribution to IT equipment enclosures (it’s serviced “zone”), thereby minimizing the number of branch circuits that must be installed in the telecommunications space. An example of how a zone PDU is used to support a pair of IT equipment enclosures is shown in the simplified graphic below.

Two (2) standard configurations of zone PDUs are utilized in VA telecommunications spaces.

The 60A input zone PDU was introduced in v3.0 of the Infrastructure Standard for

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.

mailto:%20VAITESEDatacenterEngineering2@va.gov?subject=RE:%20Single-Rack%20TR%20Design%20&%20Outfitting

Zone PDU Power Distribution White Paper

Data Center & Infrastructure Engineering 13 July 2020

Telecommunications Spaces, used to power up to three Standard Density (SD) IT equipment enclosures. The 30A input zone PDU was introduced in v2.2 of the standard, used to power pairs of SD IT equipment enclosures at a reduced total power capacity suitable to legacy VA operating environments.

Standard Density (SD) IT equipment enclosures are specified to support up to 5kW (5,000W) of IT equipment load. In older legacy VA telecommunications spaces, existing heat rejection systems are generally not capable of maintaining this density level; thus, IT equipment enclosures in these spaces are derated to only support 3.5kW (3,500W) of IT equipment load.

The chart below compares the power delivery capabilities of each of the standard zone PDU configurations used in VA.

60A Zone PDU 30A Zone PDU Total power capacity (either distribution leg) 21,600W 10,800W

Power capacity per enclosure (either distribution leg)

7,200W 5,400W evenly distributed

Derated power capacity per enclosure (either distribution leg)

5,760W 4,320W

As is obvious, the 30A zone PDU is not capable of supporting both of its IT equipment enclosures at the SD level (5,000W) simultaneously. It is capable of supporting the derated legacy density of 3,500W per enclosure.

Why are zone PDUs specified for use in VA telecommunications spaces? The primary benefits of zone PDUs are standardization of branch circuits to racks and cabinets, modularity, lower costs for circuit installations over lifecycle, and delivery of three-phase power at the enclosure level.

A single in-rack power distribution solution across all VA telecommunications spaces simplifies procurement and inventory management. Rather than custom-engineering power delivery solutions for each telecommunications space and the IT equipment installed, a single modular power solution is used to support every IT equipment enclosure (at standard density). The zone PDU solution also provides flexibility to use high density (10kW) enclosures in future data center locations that are able to support that level of heat density. Electrical topologies for all standardized power chains are shown in detail in the Infrastructure Standard for Telecommunications Spaces.

The use of zone PDUs reduces the number of branch circuits (power whips) that are necessary to deliver power to the critical load. When using the 60A zone PDU, the number of circuits are reduced from six to two. When using the 30A zone PDU, the circuits are reduced from four to two. There is an increase in the size of the conductors to accommodate the greater power being supplied, but the overall cost for the materials is significantly reduced. More importantly, Zone PDU Power Distribution White Paper

Data Center & Infrastructure Engineering 13 July 2020 the amount of labor necessary to install the power to multiple enclosures is reduced by half or two-thirds.

Additionally, fewer circuit breaker spaces are needed in the upstream distribution power panels when zone PDUs are used. This becomes increasingly important as higher-density telecommunications spaces are implemented to support future generation IT hardware and systems. The cost benefits of not requiring additional upstream distribution can be significant.

Finally, the standard zone PDUs used in VA telecommunications spaces ensure that three-phase power is supplied to each IT equipment enclosure. This has the additional benefits of providing more efficient 208V power to the IT equipment and allowing simplified phase balancing, as discussed in the Basic Guidance: 208V Power Distribution.

The use of zone PDUs does add an additional piece of equipment to in-rack power distribution topologies. However, the risk of equipment failure to the power chain supporting the IT equipment is minimal. The only components in the Zone PDU that have a common failure mode are the output circuit breakers protecting each power phase conductor. Data Center & Infrastructure Engineering has assessed that the additional risk involved to the power chains, which are 2N redundant at this level, are negligible and therefore acceptable.

Two standard configurations of the zone PDU are specified for use in VA telecommunications spaces. Alternative configurations are not acceptable without an approved variance from Data Center & Infrastructure Engineering.

• The output branch receptacles for each configuration are always L21-20R, allowing connection of the standard 20A 3-phase rack PDUs specified for use in the Infrastructure Standard for Telecommunications Spaces.

o The 30A zone PDU will have two L21-20R outputs on each redundant distribution leg (a total of four outputs).

o The 60A zone PDU will have three L21-20R outputs on each redundant distribution leg (a total of six outputs).

• The input receptacles for each configuration vary.

o The 30A zone PDU will have one L21-30R input on each redundant distribution leg (a total of two inputs).

o The 60A zone PDU will have one hardwired junction box with lugs to connect five conductors (3 phase conductors, 1 neutral conductor, and 1 ground conductor) on each redundant distribution leg (a total of two inputs).

References:

VA OIT Infrastructure Standard 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 Basic Guidance: 208V Power Distribution https://www.cfm.va.gov/til/dguide/OIT-InfrastrucStdsTelecommSpaces.pdf https://www.cfm.va.gov/til/dGuide/OIT-DGTemplates-CriticalTelecommSpaces.pdf