Residual energy sources when isolating machinery or equipment.

That's an excellent question! It is important to remember that in order to be effective, machinery uses force to achieve some type of work outcome. Machinery and equipment are specifically designed to work in very specific manners to accomplish the type of work they perform. In doing so, many machinery and equipment types use hydraulics, pneumatic, gravity, etc to help achieve the work outcome.

When machinery or equipment is disconnected from its electrical source, that doesn't mean it is safe to access yet. The residual energies of the hydraulics, pneumatic, the effects of gravity, etc may still apply, meaning the machine can still operate on a limited capacity and still injury or kill a person working on it. These residual energies need to be checked too and safety measures put into place to make these safe.