The Design and Organization of Data Centers/Electrical

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Types of Service[edit]

  • 120 V 1 phase
    • Hot, Neutral, Ground
  • 240 V 1 phase
    • 2 Hots, 1 Ground
  • 208 V 3 phase
    • 3 Hots, 1 Neutral, 1 Ground
  • 208 V 1 phase
    • 2 Hots, 1 Ground
  • 480 V 3 phase
    • 3 Hots, 1 Neutral, 1 Ground
  • 48 V DC
    • Positive & Negative

Uninteruptable Power Supplies[edit]

Absolutely necessary


Central UPS[edit]

All equipment stays up for same length of time.

Rack-mounted UPS[edit]

Put batteries where they are needed most. Easy redundancy with dual power supply computers.

Server-mounted battery[edit]

Google servers are connected directly to the AC feed with no UPS in the middle. Instead, each server has its own 12 VDC battery, which is used to power the server during power outages.[1][2]

Brick UPS[edit]

Good for smaller installations. Easy redundancy with dual power supply computers.


Loads that cannot tolerate any outage shall be placed on UPS power. Critical systems, such as the air conditioning cannot tolerate a brief outage, so they should be supported from generator power. Battery run time for UPS loads are dependent upon the budget and level of reliability required. With a well designed backup generation system, UPS runtime may be minimized since the gensets will be online in 8 to 20 seconds.

Power Interruption[edit]

Plan for unattended shutdown and restart whenever possible.

Consider remote alert of power interruption.

Make sure the KVM is also on UPS.

Make sure you have emergency lights and flashlights for working in the dark.

Estimating remaining run time

Restart of UPS after full drain

Redundant UPS systems[edit]

Rack-mounted - side to side redundancy.

Central UPS - need two of them with separate breaker boxes/PDUs and color coded system.


Determine your local outage characteristics for your power supplier. Do they tend to be infrequent, but long? Common, but short?

On-site vs delivery contract

On site minimizes need for large UPSes

Environmental issues and permit requirements for fuel storage

Layout and Redundancy[edit]

Look for computers with dual power supplies, or, less preferably, make sure you have redundant boxes per function. This allows for rearranging power cables and moving a box from one area to another without turning it off.

Maintain side-to-side redundancy by placing power strips on separate breakers or UPSes.

Remote Power Control[edit]

Remote power on and off

Resetting stuck machines and routers

Power on sequencing

Electrical Grounding/Earthing[edit]

All metal server or network racks and cabinets, overhead raceways and metallic conduit must be properly grounded to each other and to ground.

  1. "Google Unveils Custom Server/UPS/Power Supply" by Joe Polastre, April 1, 2009
  2. Slashdot: "Google Reveals "Secret" Server Designs" April 02, 2009