What grounding requirement exists for electric welders?

The requirement that the case of electric welders must be grounded unless they are powered by an internal combustion engine is crucial for ensuring safety in welding operations. Grounding the welder's case helps to prevent electrical shock hazards. When properly grounded, any stray voltage that might build up on the welder's body can be safely directed to the ground, reducing the risk of electrical injuries to the welder and nearby personnel.

In many welding applications, especially those involving high voltages or currents, there is a significant risk of electric shock or electrocution if the equipment is not adequately grounded. This requirement is particularly important for electric welders, as they are connected to an external power supply that can pose serious risks if electrical faults occur.

Other options suggest incorrect practices, such as insulating the frame or asserting that grounding is unnecessary. Insulating the frame could actually increase the risk of shock, as it would not allow stray voltages to be safely directed away. Also, stating that grounding is unnecessary overlooks the fundamental importance of grounding in preventing electrical hazards. Finally, requiring only the tools to be grounded misses the critical aspect of grounding the entire welder, which is the first line of defense against electrical accidents.