Electrical: DC, AC, shore power and corrosion

What to inspect · Power & sail

Electrical faults are a leading cause of boat fires, and older boats carry decades of add-ons. The surveyor checks AC and DC systems against Coast Guard rules and ABYC standards. Pay special attention to the shore power inlet, the batteries, and protection against corrosion and shock.

Why old wiring matters

• BoatUS insurance claims (reported in 2016) put engine electrical faults at 20% of fires, other DC faults at 15% and AC faults at 12%. On boats over 25 years old, aging engine wiring harnesses took an outsized share.
• Most of the AC fires started between the dock pedestal and the boat's shore power inlet. BoatUS suggests inspecting or replacing the inlet on boats more than 10 years old.
• Copper wire that has turned green has corroded and conducts poorly. Tangled, unlabeled wiring usually means years of owner add-ons; decide whether you face a cleanup or a rewire.

What the surveyor checks

• Batteries secured so they can't shift, terminals covered, and each circuit protected by a fuse or breaker close to its power source.
• Wiring faults that could start a fire are top-priority items, and insurers often insist they be fixed. Some standards didn't exist when an older boat was built, but insurers may still require key ones.
• If the boat has a bonding system, it should be checked for continuity.

Shore power, corrosion and shock protection

• Plugging into shore power ties your boat, through the green ground wire, to every other boat on the dock. A galvanic isolator (about $200, BoatUS, August 2026) blocks the small DC currents that eat anodes and underwater metal; larger boats may use an isolation transformer.
• Never cut the green ground wire to stop corrosion. It is the safety path if an AC fault happens.
• An ELCI is a whole-boat ground-fault breaker, set to trip at 30 milliamps under ABYC standards, which first included it around 2008. Many older boats have none. One can usually be added if the boat's AC system is free of faults.
• Never let anyone swim near docks or boats connected to shore power. Electric shock drowning has mostly happened in fresh water, but no water can be assumed safe.

Gasoline boats: ignition protection

• Boats with gasoline inboard engines or generators fall under Coast Guard electrical rules (33 CFR 183 Subpart I, first published in 1977). Electrical parts near gasoline sources must not be able to ignite fuel vapor, unless they are isolated from the fuel.
• On an older gasoline boat, ask the surveyor to confirm that starters, alternators, pumps and blowers in the engine space are rated ignition protected.

General guidance for recreational boaters, researched from the sources listed and written in our own words. Your equipment manuals, local knowledge, the Navigation Rules and a qualified instructor come first.