How far should a scissor-lift be kept from power lines?

As far as possible! Here are the OSHA requirements. If the voltage is unknown stay 18 feet away. 13,000 - 69,000 volts10 feet115,000 - 138,000 volts11 feet230,000 volts13 feet500,000 volts18 feet This is no joke, the current will arc to equipment too close to the lines, and may make it near impossible to rescue the equipment operator. It's like being struck by lightning.