This photo has been making its way around boating message boards, as some poor soul wound up with fried extension cords when he connected to shore power at an unnamed marina. Northern Lights, the marine industry’s power production experts, offers some hints and tips to help ensure that this doesn’t happen to you.
The damage seen in the photo is a result of overheating due to high contact resistance. This occurs when a connection is not tight or is not solid, and provides electrical resistance. This can create enough heat to lead to the cookout you see here.
Potential causes and their cures:
-Corrosion on either the plug (easy to look for) or the receptacle (harder to see, so use a flashlight). Important areas should be scraped clean each time a connection is made.
-Corrosion can also occur if a plug is left in place for a long time. This could be remedied by unplugging the cord and plugging it back in every so often. Do it once a month during routine maintenance.
-Weak contact spring pressure in the receptacle. This is hard to determine, especially since it could only be one bad contact out of the three, but there should be some physical resistance when the plug is plugged in and twisted to lock. If it’s a struggle to connect your plug to shore power, that should be taken as a sign to take a closer look.
-The most likely scenario is that one of the terminals has come loose from the wire. If the plug is molded onto the power cord, the wires should be crimped or ultrasonically welded to the terminal. This will make them less likely to come loose. If the plug is serviceable/removable, the wires are retained by screw terminals, and these can become loose over time. If a connection becomes loose, the resistance goes up, and generates heat when current passes through it.
-Over time, flexing of the cord can cause individual wire strands to break apart, creating heat when current flows through it. This is most likely to happen at the ends of the cord, where it is often bent to plug in, or if it hangs under its weight. After your vessel has been operating under shore power for a few hours, check the ends of the cord for heat, but do so safely. Use an infrared gun to check for unusually high heat signatures. If the cord end is unusually hot, it may be time to replace the cord or cut the cable back and re-install or replace the connector if it is of the serviceable type.
-As to the suitability of shore power at any given marina, the best thing a boater can do is to check the supply voltage with a voltmeter. Invest in a high quality meter, and you will be able to test frequency, too. Also, big hardware box stores carry test plugs that light up to indicate proper grounding and the phase rotation of the supplied power at the receptacle.
-Unfortunately, these tools won’t indicate much about the overall reliability of the power (voltage spikes, fluctuations), or if the shore power outlet is properly wired to handle its rated current. Look for indications that the marina and its electrical system are well-maintained. Are there burn marks on the shore power receptacles? What about corrosion or other visible damage? Look to see if other boaters are plugged in to shore power. Don’t be shy about approaching your moorage neighbors and asking about their experience. Check the internet for marina reviews and comments, as well as checking in regularly on cruising comment and message boards.