Faulty wiring energizes houseboat; exposes swimmers to electric shock

Incident overview

Two swimmers became incapacitated due to electric shock while swimming in a freshwater lake.

 

Regulated industry sector

Electrical, low voltage electrical system 30V to 750V

Location

Lake Cowichan

Investigation conclusions

Site, system and components

Residence on a fresh water lake with a dock and houseboat.

Failure scenario(s)

Housing of 12 volt DC /120 volt AC RV style refrigerator became energized by the shorted AC circuit. The 12 volt DC system was also connected to the aluminum hull of the boat through the engine and the grounded negative, making both systems common.

Facts and evidence

Witness statements confirmed that at approximately 4 pm on May 26^th two swimmers jumped from the top of a houseboat into Lake Cowichan and received a shock.

The houseboat wiring had been altered and an alternating current (AC) circuit was added. Non-metallic sheathed cable (NMD90) fed receptacles and fridge. The fridge was capable of running on either 12V DC or 120V AC.

Testing revealed damaged non-metallic sheathed cable shorted out to a metal device box which housed a receptacle located at the forward part of the cabin. The short to ground was able to make a path back to its source through a 12V/120V fridge that was bonded to the aluminum hull of the boat via the 12V system.

The neighbours dock had a galvanized steel cable run along it, the cable ran up the bank between the two properties to where it was connected to a power pole guy line. The guy line anchor was located approximately 7 feet from the neighbour’s service ground electrode. The steel cable was in the water directly across from where the swimmers jumped into the water. The steel cable through the guy line anchor and the neighbours service ground electrode was a good return path to the common transformer feeding both properties (See Diagrams).

Causes and contributing factors

The facts and evidence strongly suggest that the houseboat became energized by faulty wiring. This was exacerbated by the lack of GFCI protection and possibly a poor bonding connection and or voltage drop that prevented the breaker from tripping. This in turn energized the water and leaked current to the steel cable on the neighbour’s dock. The swimmers jumped directly into the path of the leaking current.

 

Impact

• Injury
  • Qty injuries: 2
  • Injury description: 2 people received electric shock
  • Injury rating: Insignificant
• Damage
  • Damage description: 120 volt receptacle and non-metallic sheathed cable melted/burnt.
  • Damage rating: Moderate

Incident rating

Moderate