A missing third prong from an electrical plug resulted in the electrocution death of a worker. He was climbing a ladder to hand a power drill to another worker when he received a fatal shock. Investigators found the extension cord was missing its grounding prong. The grounding wire and the frame of the drill were being electrified off and on by the energizing wire. The drill was not double insulated.
Grounding is not necessary for a circuit to work, it is only there for the protection of individuals from stray current. In a normal circuit, electricity flows from the “hot” wire (which is usually black) to the electrical device and back to ground potential through the neutral wire (which is usually white or gray). A ground wire (which is usually bare or green) is provided so there can be an alternate path for the electricity to flow back to ground potential if an electrical short occurs. For example, if the wires inside an electrical device have become worn or the insulation has broken down such that the hot wire makes contact with the case on the device, then the current could flow through the individual using the device back to ground. If a ground wire is present, however, the current will take the path of least resistance and flow through the ground wire back to ground instead of flowing through the individual causing an electrical shock.
Never destroy or cut off the round grounding prong on a plug to fit it into a socket or extension cord that does not accommodate the prong. If the equipment you are working with does not have a ground wire, then consider rewiring the device to accommodate the grounding feature. Another option is to use double-insulated tools. These tools have an air space around the device to help insulate you from an electrical shock.
Remember to inspect a power tool and any extension cords before you use them. If you find signs of damage or wear, discard it or turn it in for repair by a qualified person. Don’t attempt electrical repairs unless you are trained and qualified.
DISCUSS WITH YOUR CREW
- Are you aware of any extension cords or corded tools that we have that have a missing or damaged grounding prong?
- Do you know who to notify if you find an extension cord or corded tool with a damaged or missing grounding prong?
- What other defects would make an extension cord or corded tool unsafe to use?