1.He repaired and reused the defective circuit breaker without replacing it. After repairing, he judged that the breaker was no problem only by a circuit tester check. But, it is supposed that the condition of the breaker was to cause a short circuit if a voltage was impressed. (Although he has license of High and low voltage electric construction, he lacked the knowledge of a breaker.)
2.Although he had the control panel with his hand, he turned on a switch of the breaker without installing the control panel to the outlet panel after installing the breaker on the control panel.
3.He had worked wearing cotton gloves without wearing insulated gloves.