by Reza Tajali, P.E.

Data center power systems are designed with stringent requirements for power availability and quality. A common approach is to use solidly grounded low voltage power sources. These sources are tied together through various arrangements of circuit breakers with automatic transfer schemes. Because of the multiplicity of ground return paths, design of the ground fault systems for these switchboards is rather complex. However, no industry standard exists to guide the consulting engineers and users who ultimately specify these systems. This paper serves to illustrate the basic principles and the problems with solid grounding through the case history of the design of one data center. Further, this paper will demonstrate that the ideal circuit breaker for these applications incorporates two independent ground fault sensing units.