Poor equipment design and a Code violation proved to be a deadly combination.
As six-year-old Laura gazed out her living room window she saw her mother (who had been cleaning the house with an electric power washer) lying motionless in the yard. “Mommy's asleep in the grass,” she told her two older sisters. Sarah, the eldest daughter, rushed to her mother's side. As she bent down to touch her mother, Sarah received a painful electric shock and noticed the grass in the area was wet. Soon thereafter, a neighbor unplugged the pressure washer from its receptacle. Emergency medics arrived and administered CPR, but the effort failed to revive the woman.
An attorney for the widower and daughters asked me to inspect the pressure washer. As I began my investigation, I was surprised to learn a fellow electrical engineer had modified the pressure washer during his initial inspection. The engineer had discovered the ground conductor (green wire) was not properly connected to the metal frame at the motor's junction box and had corrected the problem. Although his intentions were good, he had modified evidence and put into question its use in court.
Using a multimeter, I discovered one of the two supply conductors feeding the motor registered a short circuit to the motor's frame. However, I could not find the source of the short circuit without loosening one or two external parts of the washer to get a better look inside. In light of the previous modification, the lawyer representing the woman's family thought it best to leave the unit alone.
During this first inspection, I learned the pressure washer was powered by a 1.5-hp, 3,450-rpm motor wired for 120V. The motor was belted to a high-pressure water pump with a standard rubber belt (Photo 1 in original article). A long rubber hose ran from some metal fittings on the pump to a metal hand wand, which had interchangeable nozzles that allowed the user to adjust the spray pattern and water pressure for different cleaning applications. A handle was mounted to the bottom of the wand, with an electric switch positioned as a trigger. Separate tests taken with a multimeter by myself and the first electrical engineer revealed the switch was wired on a separate low-voltage circuit that couldn't have lethally shocked the woman.
I found what appeared to be the problem in an unexpected place. The rubber hose was protected from bursting by a braid of steel stranding. This braid ran the length of the hose and was securely fastened to the fittings at each end, providing a continuous electrical path from the hand-held metal wand to the metal frame of the pressure washer. Because the motor was directly bolted to the metal frame, a short circuit in the motor would provide an electrical path to the metal hand wand.
Although the washer's power cord still had its round grounding pin in place, the grounding pin was missing from the orange extension cord plugged into the washer (Photo 2 in original article). (The deceased woman's family received a much smaller settlement because the grounding pin had been sawed off the extension cord.) Because both spades of the extension cord were small, the male connector could plug into a standard receptacle either right-side-up or upside-down. If plugged in right-side-up, the supply conductor (black wire) of the receptacle would match the supply conductor (black wire) of the extension cord, which connected to the supply conductor (black wire) of the pressure washer motor. If plugged in upside-down, the white conductor in the orange extension cord would become the supply conductor, energizing the metal parts on the pressure washer to 120V.
Nine months later, a group of 15 professionals gathered in the laboratory for a day of inspection. One of the key points of discussion centered around the short circuit between the power washer's neutral conductor (white wire) and its motor frame. They discovered the metal cover on the motor's electrical junction box had a sharp edge that may have cut the conductor's insulation and exposed its bare conductor. The lack of an outer covering or sheath had left the conductors vulnerable to this type of damage. Experts also carefully examined every nut, bolt, screw, and individual component for signs of tampering.
During testimony, we learned the mother had plugged the extension cord into a receptacle located inside the front door of the house. Because the cord wasn't plugged into a GFCI receptacle at the time of the accident, litigation focused on whether the pressure washer's power cord should have had its own ground-fault circuit protection device. It wasn't until a second pressure washer of the same make and model was involved in a similar incident that a break in the case occurred. A supply conductor (in this case the black wire) on this second washer had also been cut, leaving an exposed conductor. This fact pushed the case to settlement and hammered home the importance of proper wire protection and grounding.
Buske is a Principal with Buske Engineering, Benicia, Calif.