What is grounding?
In an AC electrical system, the wire that carries away fault currents is called the ground wire. The equipment ground allows the GFCI (Ground-Fault Circuit Interrupter) to disconnect the circuit and prevents fault current from electrifying a grounded surface. There are three main types of grounding related to shore power conversion.
Equipment Ground
As mentioned above, the equipment ground is necessary to redirect fault current. Every shore power converter must have its own equipment ground terminal connected to the ship’s hull.
Shore Ground
The shore ground originates at the dock and connects only to the input transformer fault shield via the shore ground connection.
LV Common
The LV Common ground is utilized for all small-signal AC and DC circuits. For paralleled converters with a TN-S configuration, this type of grounding is accomplished via the equipment ground. For paralleled converters with an IT configuration, this grounding is accomplished via a separate three-conductor cable passing between converter cabinets.
Why is it important?
According to statistics reported by ESFI, between 2003 and 2007 electrocution was ranked as the 6th most common cause of fatal accidents in the workplace. To combat the danger of electrical accidents, OSHA has published specific regulations for grounding including requirements specific to shipyards and general marine operations.
Safety and Compliance
When shore power enters the boat it has the potential to also enter the water surrounding the boat; this creates a serious shock hazard for nearby swimmers. Leaky fault current can also electrify nearby surfaces and endanger anyone on board the ship as well as the equipment. Grounding electrical systems greatly reduces the risk of potentially fatal electric shock. Proper grounding also protects on board equipment from serious damage.
Problems Caused By Grounding
Although the ground provides a path for fault current to return to the source, it also exposes the boat to electro galvanism. Electro galvanism causes galvanic corrosion, which eats up expensive metal equipment. To combat this side effect, it has become standard practice to use a galvanic isolation transformer, such as those found in every ASEA shore power converter. Isolation transformers also offer an indirect connection to the boat via a magnetic field for increased safety and protection against polarization.
Learn more about how isolation transformers can protect you and your boat here.
The Bottom Line
Grounding is necessary for electrical systems on board any vessel in order to:
- Prevent potentially fatal shocks on board and in the water.
- Protect on board equipment from costly electrical damage.
- Comply with local requirements to avoid fees and rework.
References
Chao, E. L. (2002). Controlling Electrical Hazards . Retrieved from United States Department of Labor: https://www.osha.gov/Publications/3075.html
ESFi. (2018). Workplace Injury & Fatality Statistics. Retrieved from Electrical Safety Foundation International: https://www.esfi.org/workplace-injury-and-fatality-statistics
OSCHA. (2010). 1926.600 – Equipment Standards. Retrieved from United States Department of Labor: https://www.osha.gov/laws-regs/regulations/standardnumber/1926/1926.600
OSCHA. (2015). Shipyard Industry Standards. Retrieved from Occupational Safety and Health Administration: https://www.osha.gov/Publications/OSHA_shipyard_industry.pdf