IEC 60255-11:2008 specifies the general requirements for a.c. and d.c. power supplies, for measuring relays and protection equipment for power system protection, including the control, monitoring and process interface equipment used with those systems. The objective of the tests is to confirm that the equipment under test will operate correctly when energised and subjected to dips, interruptions and alternating components (ripple). The main differences with respect to the previous edition are as follows: addition of voltage dips and interruptions test in a.c.; addition of gradual shut-down/start-up test; addition of reversal of d.c. power supply polarity test.