A yearlong experiment by the Federal Energy Regulatory Commission with the nation’s electric grid could mess up traffic lights, security systems, and some computers — and make plug-in clocks and appliances like programmable coffeemakers run up to 20 minutes fast.

Officials say they want to try this to make the power supply more reliable, save money, and reduce what may be needless efforts. The test is tentatively set to start in mid-July, but that could change.