OSHA allows only very limited wotk on live equipment. Troubleshooting is the most common reason to work equipment live. There are very few others and they involve equipment where the deenergization of the equipment would introduce more serious safety hazards. Some chemical processes fall into this catagory. Even when OSHA permits work on "hot" equipment, special PPE (personal protective equipment) is required. 1000 volt rated tools and gloves is the minimum. If the energy level is high then much more is required, up to and including full head covering with flash protective lens and full insulated nomex (or other flame resistant) outer clothing. Non-electrically qualified people can not be within 3'6" of any exposed energized electrial equipment of any voltage above 50 and less than 750 volts.
These rules have been in OSHA for at least 10 years and the industry is just now starting to follow them. Also look at NFPA 70E, Standard for Electrical Safety Requirements for Employee Workplaces.
LOTO= lock out/tag out
