Boat Wiring Important Knowledge For Boaters
A basic understanding of marine electrics, including boat wiring, is good knowledge for all boat owners and skippers. It is essential for boaters wanting to be independent at sea and critical for those aiming to maintain or restore a boat. This article outlines some elementary points.
Virtually all boats are equipped with a DC electrical system with power flowing at either 12 or 24 volts. These systems are typically configured with so-called two wire cabling meaning that all electrical devices are connected with an insulated positive wire and negative wire. The hull is never used for the ground because it can cause corrosion.
A two-wire system is usually grounded by completing a connection to the vessel engine. This connection effectively polarizes the system because the engine and its connecting parts (such as propeller shaft) provide a ground plane. Because of this polarization a two wire, one pole grounded configuration is often called a polarized system. The hull is not used for the ground because it can cause corrosion.
All the cabling in a two wire, insulated system is stranded. Solid cabling is not used since it is more susceptible to vibration breakage compared to stranded wire. By the same token, very fine stranded wire is best avoided since if it is too fine, it is prone to corrosion.
The insulation material used to coat the cabling should be rated as both moisture resistant and flame retarding. Insulation for cabling in the engine and bilge areas should additionally be oil resistant. Split, frayed or cracked insulation should be promptly replaced. The engine and bilge areas generate difficult environments that can erode insulation with time so regular inspections are appropriate.
Wiring should not be positioned in the bilge area if it can be avoided. All wiring that must, by necessity, be routed through the bilge should be positioned as high as possible so as to minimize the risk of it becoming submerged in water. Similarly, wiring should not be routed in areas where they are likely to suffer mechanical damage or spaces that systems liable to emit corrosive vapor.
Cabling should be installed without kinks or sharp ends that might promote metal fatigue and wiring fracture. Similarly, cabling should be fixed so that it does not flex or move with vessel vibrations. To conform with this requirement, wiring is supported at intervals of no greater than 18 inches (45 centimeters).
Water that may run along boat wiring must not be able to enter connections or electrical devices. Drain holes should be drilled in conduits or troughs that carry electrical cabling to prevent water pooling. Wires should approach terminals and devices from below and be fitted with drip loops if necessary.
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