Grounding Wires for Boat Equipment

Sometimes individual pieces of gear are grounded directly. In European-built boats, look for green wires with yellow stripes.

20th August 2013.
By Ed Sherman

Question: Recently I was snooping around in the bilge area of my new boat and I ran into the green and yellow wire attached to a bronze stud in my bilge. The stud appears to go through the hull bottom. I have no clue about what this wire does or what purpose it serves. Any ideas on what this wire is doing?

Trace this grounding wire back to the equipment it's attached to in order to find out what it's protecting.

Trace this grounding wire back to the equipment it’s attached to in order to find out what it’s protecting.

Answer: I can say for sure that the cable in the photo you sent in is serving as a grounding conductor, or as the Europeans refer to it, “earthing.”  I can also say that although you didn’t tell us, your boat was built in Europe unless it was made here in the US by Island Packet. The reason for recognizing this is that wire color code standards allow for the use of either green, or green with a yellow stripe, as appropriate for grounding conductors.

Here in the US the only builder I’m aware of that uses the green with the yellow stripe option is Island Packet. They actually use both the plain green and the green with yellow stripe. They use both options as a means to differentiate between grounding and bonding conductors throughout their boats. The differences there are a topic for another day. The Europeans have always favored the green with a yellow stripe option for their grounding conductors.

What I can’t tell you by looking at your photo is which piece of equipment is being grounded by the wire. Trace it back to the equipment to learn that. Whatever the component is, it appears that the designers wanted an isolated grounding system for their device. That’s what you have.

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About the author:

Ed Sherman

Ed Sherman is a regular contributor to, as well as to Professional Boatbuilder and Cruising World, where he previously was electronics editor. He also is the curriculum director for the American Boat and Yacht Council. Previously, Ed was chairman of the Marine Technology Department at the New England Institute of Technology. Ed’s blog posts appear courtesy of his website, EdsBoatTips.

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