Surveyor’s Notebook: No Wire Nuts Near Salt Water

Wire nuts are fine for shoreside domestic use, but should never be allowed anywhere near salt water, and especially not on a boat. Using them in a damp bilge is especially foolish

I see wire nuts on boats all too often. Many times they are installed by an owner as a temporary measure, “just to make sure it’s working,” or by electricians more used to working on houses than boats. Just to be clear—wire nuts have no place afloat, and if I see them soon after stepping aboard a boat, I know there is almost always more bad news to come.

Wire nuts and seawater make poor bedfellows. Wires that are simply twisted together can easily work loose as a boat moves and vibrates. And when water finds its way in (as it soon will), the inferior metals in the wire nut quickly corrode and increase electrical resistance.

Perhaps most importantly, you often find these connections very close to bilge water, potentially creating a path to ground and a distinct possibility of electrolysis, leading to the swift destruction of underwater metals and the depletion of the boat’s batteries.

I’ve even seen wire nuts used on 120-volt cables, a practice that can potentially kill someone. All wire connections should be made with crimped marine-grade terminals. If there is any possibility of them getting wet, they should also be covered with adhesive-lined heat shrink.

Lifelong boat addict and marine surveyor Mark Corke can be reached at

Photo by Mark Corke; Illustration by AMR

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