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In-Cabinet Seismic Response Spectra

Helping clients define practical test requirements

Project Objective

Kinectrics' customer needed replacement components qualified for installation within a Motor Control Center (MCC), but had only the original seismic qualification data for testing of the entire MCC versus the specific location where the replacements would be installed.  It was impractical to re-test the entire MCC. Therefore, to qualify the replacements, data for specific in-cabinet required response spectra needed to be developed.

Scope of Work

This project consisted of reviewing the original seismic qualification test report for the MCC, extracting information recorded from various accelerometers during the testing, and deriving suitable required response spectra that could be used to qualify the replacement component.

The Kinectrics Solution

  • Kinectrics obtained the original qualification test report from the customer and pulled over 110 test plots from the report to be used in the analysis.
  • The test plots were manually digitized to extract over 3000 individual data points from the control and survey accelerometer output.
  • The data was analyzed to determine worst-case, frequency dependent observed amplification at various locations within the MCC relative to the MCC anchorage location.
  • The amplification factors were applied to the MCC base required response spectra, to obtain amplified required response spectra relative to survey accelerometer locations throughout the MCC.
  • Using the amplified response data, a composite envelope of all likely locations where the replacement item could be installed was developed in each of the three orthogonal directions.
  • The composite envelope response spectra were then established as the location-specific required response spectra to be used to seismically test the replacement items.


When location-specific required response spectra are not available, customers often choose one of three options, i.e.


·         Specify a generic level requirement
·         Specify a test to the facility’s physical limits
·         Use survey accelerometer data from original tests directly
All of these options tend to apply considerable conservatism, which is technically defensible, but may result in over-testing and component failure during the test. By carefully analyzing the data and back-correlating data to the initial requirements, excess conservatism is removed, location-specific response spectra remain just as defensible, and the risk associated with establishing a requirement that is too conservative, is eliminated.