Planning of maintenance should take into account the condition of the different pieces of equipment instead of having a prescribed interval of certain number of years.

The working group A3.43 of CIGRE, an organisation for high-voltage electrical technology, studies maintenance strategies for circuit breakers, a key component in electric grids. It has compiled a 46x39 matrix, which maps the connection between failure modes and diagnostic methods as estimated by experienced engineers. Each element is a number from 0 to 3, where a higher number indicates a clearer connection between them.

In order to understand better how the failure modes and the diagnostic methods are related to each other, a clustering method is applied to the matrix. The chosen method is a hierarchical clustering, where both rows and columns are reordered using the Euclidean and the Manhattan distance function.\cite[p 301]{cha2007} The result is presented as a heatmap with dendrograms showing the possible clusters in the columns and the rows, respectively.

The results are graphs that give a comprehensive picture of how the failure modes and the diagnostic methods are related. This is valuable for newcomers in the field. The Manhattan distance function gives less value to elements in the matrix.