Article by Capt. Steve Katz
The Green Wire
As with the other columnists here in the Coastal Fisherman, our columns usually contain real world stories and information, not many theoretical textbook columns here! The topic for this week’s article comes from popular questions and on-board service of electrical systems the past few weeks.
Throughout the day, I am asked a lot of questions regarding electrical and electronics. While some questions will have a few correct answers and dependencies, the use of the green color jacketed wire within a boats electrical wiring has no wiggle room – there are standards regarding the many uses of a green wire.
The term grounding and bonding are often used interchangeably and often misunderstood, since they both use a green colored wire. Let’s review how these are used on a typical fishing boat:
- A green wire is used as an electrical interconnection wire for bonding of metals, usually all underwater metals are interconnected as part of a cathodic protection system to help prevent against galvanic and stray current corrosion. ABYC (American Yacht and Boat council) specifies that this wire be no less than 8 AWG.
- A green wire is part of the grounding conductor in an AC or DC electrical circuit, this is a non-current carrying conductor used to help prevent shock hazard and electrical fire prevention. This wire shall not be smaller than one size under that required for current-carrying conductors supplying the device and not less than 16 AWG.
Let’s review each system
For those who don’t want to read to the end of the column, here is the punch line – The Bonding circuit and the Grounding circuit are two distinct and independent electrical circuits. The Bonding green wire circuit and the AC or DC grounding green wire are interconnected at ONLY ONE POINT on the boat, the engine negative terminal or the DC main negative bus.
BONDING
This is for the protection of metallic hardware that extends below the hull into the seawater. A complete bonding system is an electrical interconnection of underwater metallic components such as through hulls, struts, rudders, shafts and zincs.
Without a bonding system, the combination of individual dissimilar metals in a common electrolyte (saltwater) will create a “battery” with some metals acting as anode and some metals acting as a cathode. A small electrical current is naturally created between the anode and cathode, where electrons leave the anode and travel to the cathode. Depending on what metals are nearby, and their natural voltage potential determines which is the anode and which is the cathode. Luckily for most boaters, this problem is solved by using a sacrificial anode (most commonly a zinc but could be aluminum or magnesium etc. depending on the boat and water etc.) that acts as an anode for most common underwater metals used on a boat. The sacrificial anode (zinc) will slowly “wear” or loose electrons to protect the other underwear metals from becoming an anode. This Galvanic corrosion is a DC electric system not to be confused with what boaters refer to as a stray current, which is an AC or alternating current electrical system that too can cause similar corrosion problem on a boat.
One popular mistake boaters often make is that they think if one zinc is good, more is better. This is not the case, a properly designed bonding system will have the proper underwater voltage potential, too little or too much of a sacrificial anode (zinc) can cause problems with galvanic corrosion.
GROUNDING
In general, the color green is used for grounding, similar to the land-based use in residential and commercial electrical wiring. Though just looking at the wires color on a boat is not enough to understand its purpose unless you know how it is connected. The use of the green wire in a power supply circuit is to act as an electrical safety ground for AC (Alternating Current) supplied by shore power or a generator. This is similar to the household wiring in color and function. Alternating current uses at minimum, a pair of electrical wires to carry current 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 will act as a secondary electrical path in the event of a short circuit at any of the AC appliances on board a boat. Without this green ground, the electrical current could flow to a person as a ground – which would be felt as an electrical shock. A properly wired ground will allow the leaking electrical current to flow to the earth ground and trip the circuit breaker, shutting of 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 a 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 the 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 can be avoided if a GFCI outlet or ELCI breaker is used, in a residential application and often on boats, a GFCI outlet is used in 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. Retrofitting GFCI outlets on a boat may not be desirable but installing a similar special breaker to protect the whole boat has become common practice and is required on new boats since 2014. The device is called an equipment leakage circuit interrupter or ELCI. This functions similar to a GFCI outlet but protects the entire boat at the entry point of the shore power connection.
While the green wires on your boat may all look alike, there serve drastically different purposes. Improper connections to the green wire may cause problems for your boats systems and or passengers.
Steve Katz
