[en] The seismic response of light secondary systems such as pumps, valves, control devices, and piping systems in a power plant is produced by the response of the primary structural system to the seismic ground motion with the result that very high accelerations can be induced in such secondary systems. This response can be reduced through the use of base isolation. In a series of experiments designed to evaluate the effect on equipment response of three forms of base isolation system, a large-scale structural model was subjected to dynamic testing on a shaking table. Each of these systems - a fully isolating system of elastomeric bearings only, a friction-damped system, and a system incorporating bearings and an energy-absorbing device - produced substantial reductions in the seismic response of the secondary structural components. Each, however, also gave rise to unanticipated behavior. A system in which the advantages of greater protection and ease of design afforded by base isolation would be realized and the undesirable side effects minimized, could be achieved by a combination of base isolation principles, the particular combination to be determined as the result of further research work