Wire is cheap and the labour of replacing it isn't, so surveyors read the printing on the cable. UL 1426 is the North American standard for cable built for boats: finely stranded so it survives vibration, with insulation rated for heat, oil and wet bilges.
What it covers
UL 1426, Electrical Cables for Boats, sets the construction and testing of insulated boat cable. In our words: conductor stranding, insulation and jacket materials, temperature and voltage ratings, and the marking printed on the cable. The text is sold by UL.
A typical listing, from Cobra Wire's catalogue: UL 1426, BC-5W2, rated 105°C dry, 75°C wet, 600 V for AC and DC circuits, Class K tinned copper stranding. The catalogue's jacket legend prints the maker, size, number of conductors, voltage, temperature ratings and BC5W2.
Where it's cited. Practical Sailor notes ABYC recommends wire meeting UL 1426 and SAE J378. For boats under 33 CFR 183, section 183.435 lists a conductor meeting UL Standard 1426 among the accepted conductors for circuits of 50 volts or more.
What surveyors check against it
The printing. Read the jacket. Boat cable carries its standard and rating along its length. Unmarked cable is a question for the owner.
The stranding. Household cable is usually solid core, made to sit still in a wall. Boat cable is finely stranded so it bends and vibrates without breaking. Look where a cable has been cut back at a terminal.
Household cable and fittings. Practical Sailor didn't test wire nuts at all, because they don't meet any marine code. Solid-core cable and household connectors behind panels are the usual finds on boats wired by owners. See household wiring.
Heat. Discoloured insulation near terminals or in bundles. Cable ratings matter because ampacity falls in engine spaces and bundles, which the fuse size calculator allows for.
Citing it in a finding
Cite the cable and where you found it: "Solid-core household cable, unmarked, feeding the cabin lighting circuit behind the saloon panel. Replace with finely stranded marine cable to UL 1426, per ABYC E-11." For AC circuits on boats covered by 33 CFR 183, cite 183.435 as well.