Why do welding equipment need protective grounding?

Two welders, A and B, were spot welding a metal casing at a factory when they discovered that one lead coil of the welding machine was broken. A found a piece of flexible wire and asked B to replace it. While replacing the wire, B noticed that the bolts on the primary connector plate were loose and tightened them with a wrench. A was not present at this time. B then made a few trial welds and left the work area. When A returned, unaware of the situation, he began spot welding, but collapsed after only one weld. Worker C immediately cut off the power, but also died due to delayed rescue.

The main causes of the accident were:

(1) A short circuit was caused by the coil touching the welding machine casing due to a burnt-out connector plate.

(2) The welding machine casing was not grounded.

How can this accident be prevented?

(1) Equipment maintenance should be performed by an electrician.

(2) Welding equipment should be protectively grounded.