Here is a similar excerpt from a safety sheet: "GUIDELINES FOR THE USE OF SCISSOR LIFTS (ELEVATING WORK PLATFORMS) AND AERIAL BOOM LIFTS (EXTENSIBLE BOOM PLATFORMS)";
- Use caution when working near lines of lower voltage.
Aerial lifts rigged with electrical lighting, special effects, or grip equipment should not be operated over low voltage electrical utility lines (600 volts or less), including supply lines for residences.
In this context it's clear that "over" means "located above" -- in other words, the lift should not be physically above lower-voltage power lines, possibly because of the danger of the lift collapsing onto the power lines and causing a short or a fire or some other unwanted and dangerous result.
(I'm not an experienced electrician and so I don't understand why this would be more of a danger than if they are located over higher-voltage power lines. It seems to me a bad idea to locate a lift over any power lines, but I suppose there is less danger if the lines carry similar voltage.)
Gustavson's answer would be correct if the context meant that the lifts were powered by the lower-voltage electrical lines, meaning that the lines might not provide enough electricity to safely operate the lift. However, it does not seem like the right definition in this context.