There is no exact number of repetitions to be measured. The size of the sample depends on the desired analysis. The larger the sample size, the more reliable the results.

For energy consumption measurements in a controlled environment, we recommend a minimum of 30 repetitions. In this way, the sample distribution will tend to be normal regardless of the population distribution.

Refences:

• Field, A. (2013).  Discovering statistics using IBM SPSS statistics.