Abstract: A maintenance worker was assigned to connect an electric welder to a 480-volt circuit. To identify individual conductors, he asked a coworker to activate switches in a panelboard. The maintenance worker used a small digital tester to test the conductors as the other employee opened and closed the switches. The maintenance worker asked the coworker to close switch #3. When that was done, the maintenance worker immediately said to open it. When the coworker complied, the maintenance worker jumped or was thrown back and fell to the floor. He had apparently been in contact with a circuit part when the switch was closed. He did not respond to employees. Emergency medical services arrived, but they could not revive him. He had been electrocuted.