Effect of continuous (intermittent) use on the power output of domestic microwave ovens

The power output of five recent domestic microwave ovens (on the market 2003/2004) was measured using a standard 1000 g water load during 30 min of continuous use. The power output of the ovens declined significantly (P <= 0.05) in the first 5 min of use, ranging from a minimum of 7.0% to a maximum of 19.7%. Further but not always significant declines (P <= 0.05) were measured after 20 min of continuous use. No significant reductions were measured between 20 and 30 min. Overall, the mean reduction in power output after 30 min of continuous use was 17.3% for these five ovens compared with 13.5% for five ovens in a previous study. Based on trials carried out approximately a decade apart, there has not been any improvement in the performance of domestic microwave ovens in terms of the decline in power output after continuous or prolonged use. The authors believe that many users, including consumers, caterers and those using domestic microwave ovens for research purposes, would benefit from a greater awareness and understanding of how the rapid reduction in power output in the first 5-20 min of use is likely to affect the expected heating performance.