The correct answer is A) contactors and relays are mounted on non-conducting panels. Motor controllers are less prone to grounding issues because the contactors and relays that control the motor circuits are typically mounted on non-conducting, insulating panels within the controller cabinet. This insulating mounting prevents ground faults from developing, as there is no conductive path for current to flow to ground. The other answer choices, while potentially relevant in some situations, do not directly address the reason why motor controllers are seldom troubled by grounds. Shock mounts can help reduce vibration, special insulation can protect critical circuits, and cabinet heaters can prevent moisture, but none of these factors specifically address the non-conducting mounting of the control components.