Article by Capt. Steve Katz
The Green Wire
A quick look at the electrical wiring on your boat will easily demonstrate how popular green wiring is in a vessel. What make this green wire so popular and what is its purpose?
In general, the color green is used for grounding and bonding on a boat, similar to the land-based use in residential and commercial electrical wiring. Though just looking at the wire’s color on a boat is not enough to understand its purpose unless you know how it is connected.
The most common use of the green wire is to act as an electrical safety ground for AC (Alternating Current) that is supplied by shore power or your generator. This is similar to household wiring in color and function. Alternating current uses at minimum, a pair of electrical wires to carry power to an appliance, light or other consumer of electricity. The green ground wire is NOT normally a current carrying conductor unless there is a fault in the appliance, equipment, wiring, etc. This green grounding wire is often referred to as a safety ground.
This green wire can act as an alternate electrical current path in the event of a short circuit at any of the AC appliances on board.
Without this green ground, the electrical current could flow to a person as a ground – which could be felt as an electrical shock. A properly wired ground will allow the leaking electrical current to flow to the ground and therefore tripping the circuit breaker, shutting off the source of power to the defective appliance or circuit.
All the green safety ground wires are tied together at a single common point on a boats electrical system, usually behind the main panel.
What if there is an electrical problem that is not a direct short, but a low amperage “leak” due to faulty equipment or wiring? In this case there is not enough loss for the circuit breaker to trip and the small amount of electricity ends up on all the interconnected green wires. This current may go unnoticed until somebody gets shocked when touching something metal on-board or while in the water near the boat.
This shocking situation is avoided if a GFCI outlet was used. A GFCI outlet is used in residential bathrooms, kitchens and other wet or damp areas. This type of device recognizes an imbalance of electrical flow and trips when there is electrical leakage. Installing GFCI outlets on everything that uses AC power on a boat is not practical, but installing a similar special breaker to protect the whole boat has become common practice in new boats and required on most new boats since 2014. The device is called an equipment leakage circuit interrupter or ELCI and functions similar to a GFCI outlet, but protects the entire boat at the entry point of the shore power connection.
Many marinas have begun updating their electrical system to meet new regulations and have installed Ground Fault Protection (GFP) or Ground Fault Equipment Protector (GFEP) breakers at the shore power pedestals. If the boat has electrical leakage, this shore-based breaker will trip and shut off power until the on-board problem is fixed. Often boaters do not know if they have problem until they plug into shore power at a marina with a newer electrical system. This shore-side solution is to help ensure electrical shock safety for all boats, especially those who do not have an ELCI onboard. In addition to helping to prevent on-board problems, these systems help prevent drowning deaths (Electric Shock Drowning) most common in freshwater where the boat’s leaking electrical current energizes the water around the boat and shocks and drowns swimmers or anybody in the water near the boat.
If your boats shore power circuit is tripping one of these safety devices, the exact problem within the boat can be difficult to find and can cause problems between marina staff and the boats crew.
Some common sources for electrical problems relating to shore power imbalance/leakage are:
•faulty power cord, splitter or smart Y adapters
•corroded electrical connections
•faulty galvanic isolators, washers and dryers, hot water heaters, battery chargers, ice makers, refrigerators, air-conditioning control boards, inverters and generator transfer switches.
This is not an inclusive list, but a good place to start if your boats electrical system is having a problem.
If you are experiencing a problem, one way to narrow it down is to turn off power to all devices on the boat by turning off all alternating current breakers on the boat and then try connecting to the dock. If that doesn’t trip the dockside beaker, then turn on one circuit at a time until you find the problem circuit or circuits. Then you can investigate that circuit and the connected devices. If the dockside breaker still trips with all of the breakers off, then the problem is isolated to the shore power cord and connected hardware before the main electrical panel.
For those interested:
•A Ground Fault Protection (GFP) breaker trips at 100 milliamps, Ground
•Fault for Equipment (GFEP) trips at 30 milliamps, Equipment Leakage
•Circuit Interrupter (ELCI) trips at 30 milliamps and a Ground-Fault
•Circuit Interrupter (GFCI) receptacle trips at 5 milliamps.
Green wire on a boat also serves as another important function in creating a bonding system for underwater metals, which we will cover in Part II next week.
Captain Steve Katz is the owner of Steve’s Marine Service and holds NMEA, AMEI and NMEA2000 certificates along with ABYC Master Technician certification and factory training from many manufacturers. To reach Steve, call 410-231-3191.
