In my previous posts, I’ve discussed the green power savings achieved by using DC power to operate the data center. I’ve also discussed some design considerations for insuring the greenest performance of the DC power plant. In this post, I’ll be talking about one of the things that gets neglected the most, grounding.
Good solid grounding is critical for efficient operation of a data center. It’s critical for proper operation of AC power systems. Grounding the neutral of split phase (240/120VAC) or wye (208Y120) is important to insure the voltage stability. Certain delta power may be grounded for safety (“corner grounded delta”).
On the DC power plant, what is commonly referred to as ground is the return to the power plant (battery is the supply lead from the DC power plant, return completes the circuit back). Per standards, the return side of the DC power plant is required to be connected to the AC power ground. In addition to the safety aspect, this makes the DC power by providing a path for noise created by the AC power system. Additionally, this adds safety in case AC power gets crossed with DC.
One of the most critical parts of the ground system is the connection to the earth. No connections to water pipes! As long as there is at least 6 feet of earth and you’re not in a dry area like the desert, I recommend a ground plane made of three ground rods driven in a triangle approximately ten feet per side and connected together.
In cases where the ground rods can’t be driven, usually because of rock close to the surface, it may be required to bury the ground rods horizontally. In extremely dry areas, it may be necessary to drive the rods deeper or use more of them. The important thing is to get as good an electrical connection to the earth as possible.
The ground cable should be generously sized, copper, and is expected to be thermally welded where it’s spliced. Alternatively, brass compression connectors will serve. The important thing is to make sure that all connections are electrically and physically solid.
The optimal configuration is to use copper buss bars at the interconnection points and avoid splicing the cable at all (believe me, you don’t want to be trying to weld 4/0 cable).
For more information on grounding DC power systems, I recommend picking up a copy of ANSI J-STD-610.
Ground your data center DC power plant properly and you’ll be safe, reliable, and the greenest shade of green.
Vern, SwiftWater Telecom