Household wiring on a boat: solid core cable, wire nuts and how surveyors write it up

Household cable is made to be stapled inside a wall and left alone for 50 years. Inside a boat it's flexed, vibrated, soaked in salt air and run next to engines. The solid conductor work-hardens and cracks, the wire nuts loosen, and a joint that's loose carries current through a smaller and smaller contact until it gets hot.

What marine wiring looks like

Practical Sailor notes ABYC recommends wire meeting UL 1426 and SAE J378. Marine wire is finely stranded, with good insulation, so it bends and vibrates without breaking. Connections are crimped terminals, sealed with heat-shrink where moisture gets in. Practical Sailor didn't test wire nuts at all, because they do not meet any marine code.

Tinning is a bonus. Practical Sailor's other piece points out ABYC has never mandated tinned wire.

How a surveyor checks it

Open the panels, lockers and any lining that comes off. Read the cable: household cable usually has solid conductors; marine cable is marked with its standard and is finely stranded. Look at every joint you can see for wire nuts, twisted and taped connections and household connectors. Look for heat: discoloured insulation, melted plastic, brown terminals.

Additions by owners are where it's usually found: an AC outlet, a water heater, a reading light.

What decides the grade

Heat and place. Overheated household wiring, or household AC cable in the engine room or bilge, is an A. Household cable or wire nuts elsewhere is a B. A small amateur connection in a sound marine system is a C.

What the fix costs

Photos to take

The cable markings, each bad joint, any heat marks, and where the cable runs. With Axsail, say which circuit it is as you take each photo and it goes on the electrical finding.

Writing it up

Name the circuit, the cable type, the connections used, any heat damage and where the cable runs. With heat damage, say the circuit was isolated and shouldn't be used.