Pre-Purchase Inspections
September 2009 - Electrical Grounds

There's an old axiom about salt water and electricity not mixing very well. Of course any boat owner knows this all too well and yet, the vessels we cruise aboard are awash in electrical and electronic equipment, cables, terminals and bus bars. Take for example the electrical terminals and the way they provide a link between a wire and a termination, typically a screw or bolt. Under ideal conditions this connection should afford a very low resistance, electrically "transparent", connection. To ensure this occurs it's important that only high quality materials are used, such as Type 2 or Type 3 tinned wiring, tinned two stage crimp terminals and a clean connection that's free of paint, oil, dust, salt and other contaminants. Two stage crimp terminals allow the installer to crimp both the conductor as well as the wire's insulation, the latter affording a highly desirable measure of strain relief to the installation. If such a terminal is employed, it's important that the installer crimp both stages. During my inspections I frequently encounter the second crimp unused.

The wire "Type" refers to the fineness or number of strands per conductor. Solid, Type 1 conductors that are used ashore are not approved for marine use for two primary reasons. First, they cannot absorb flexing and vibration without failure and second, they are not designed to be terminated with a crimp-style connector.

The image shown in this month's ad, taken aboard a vessel undergoing an SDMC Systems Inspection, shows an example of a quality tinned crimp terminal. It is installed using a section of heat shrink tubing for strain relief and to prevent water migration and corrosion. So far so good. This is a large cable that's used for an engine block ground, which means it is transmitting high current each time the engine is started and probably for alternator charge output. The fault lies not in the wire or the terminal but rather in the manner in which it's been attached to the engine. The ring terminal has been installed over a thick layer of paint. And, coolant has leaked onto the connection. Paint is an insulator rather than a conductor, so this connection's resistance is probably much higher than it should be, while the antifreeze surely doesn't help. It's likely that all of the current is being "pulled" through the fastener's threads, which is less than ideal. Additionally, the terminal has been installed over the oil pan flange rather than directly to the engine block, which once again ensures that the fastener threads become the primary source of conductivity between the cable and the engine. At best the result is a poor connection, which may lead to an engine that might not start or an alternator that may not charge when needed. At worst connections of this sort may lead to overheated cables and possibly a fire.

If you’re interested in finding out more about pre-purchase inspections, vessel selection assist, the Captains’ Club (simply click on these words to be taken to the relevant sections of this website) or other services offered by Steve D’Antonio Marine Consulting, send an email or call 804-776-0219.