PS Advisor April 2018 Issue

Keeping the Shorepower System Safe

One of the often overlooked maintenance items in the pre-season rush to the water is the AC shorepower system. Over the years of surveying, I’ve amassed a small collection of scary photos from past surveys showing the common examples of neglect to this critical system.

Barring improper use or some owner fabricated MacGyverism gone bad (jury-rigged adaptors, botched plug installations, etc.) overheating and corrosion are the primary causes of AC shore power cord problems. Charred plugs and receptacles are the most common and are a result of resistance build up due to loose or corroded connections, which in turn generate heat and the potential for fire. The problem is especially prevalent among boats that continually run high energy loads such as water heaters and air conditioning units.

shorepower
Photo by Frank Lanier

A poor connection at the boat’s shorepower inlet nearly started a fire.

Basic inspections of your AC shore power system are easily accomplished and are well within the ability of any boater. The first step is securing all AC power to avoid accidental shock hazards. Turn off your boat’s main AC breaker, then the shore pedestal breaker. Next unplug the shore power cord and verify that all other sources of power (such as power on-demand generators and DC to AC inverters) are turned off and their respective breakers secured in the off position.

Start your inspection with the shore power cord itself, ensuring it’s constructed of proper marine grade components, uses appropriately sized wiring, and is the shortest cord that will get the job done. Always replace cords that show signs of chafe, cracks, split insulation, or those having electrical tape repairs.

Industry standards call for shore cords to have molded-on plugs with sealing flanges or appropriate weatherproof boots. The plugs themselves should be checked each time you disconnect shore power (prior to getting underway for example) or monthly at a minimum, particularly for discoloration or corrosion on or around pins and plug inlets.

By the time discoloration is visible at the front of a plug or inlet, you’ll typically find that the damage is greater upon opening up the back for inspection. If left uncorrected, the damage will snowball (due to increasing resistance and heat buildup) until it burns a hole through the face of the plug, possibly leading to a fire.

When inspecting your shore power cord it’s also crucial to check the dock pedestal outlet and your boat’s inlet receptacle, ensuring both are corrosion free and undamaged. Upon finding a charred power cord plug, many owners simply replace it or the cord itself, only to find the new one shorts out due to a burned dock receptacle or inlet.

Another good practice is checking the “feel” of the connection when plugging in. Those that feel loose or don’t seem to be making firm mechanical contact likely won’t provide good electrical contact either. Avoid using worn or damaged pedestal plugs and report them to marina personal as soon as possible.

Practical Sailor has looked at a variety of “smart plugs” that warn owners of problems. These include the SmartPlug (PS, June 2010), which watches for shorts, and the West Marine GalvanAlert (PS, October 2009), which checks for wiring defects and reverse polarity. For more on AC safety, see our five-volume eBook series “Marine Electrical Systems,” found at www.practical-sailor.com/books.

Capt. Frank Lanier is an accredited marine surveyor with over 30 years of experience in the marine industry. His website is www.captfklanier.com.

Comments (3)

P.S. The GalvanAlert mentioned in the article was discontinued both by West Marine and by its maker, Marinco, a few years ago. I confirmed this personally with by calling Marinco last fall when I tried to buy it but was unable to locate a retailer with stock. Too bad, it was a good idea.

Jeff Adams
S/Y Zephyrus
Bavaria 38 Ocean
Bainbridge Island, WA

Posted by: SY-Zephyrus | April 15, 2018 1:26 PM    Report this comment

This article couldn't be more timely! We spent the night aboard last night and realized that our main 30 amp breaker was tripping with less than 10 amps of load. We went to bed falsely concluding that the Magnum 2012 inverter charger was simply working too hard to keep our large but old house bank of AGMs topped off so we shut it off at the breaker before bed.

Woke up to a constantly tripping main so I turned of the breaker on the shore pedestal, opened up the access panels and started sniffing for that burnt electrical smell and feeling for warmth on the wires.

In no time I found a "hot one" coming off the back of my Smartplug shorepower inlet on the transom. It also failed the sniff test. We had a spare aboard, replaced it in no time and have been running full power for an hour with no issues.

Lessons:
1. If the shore power cord may have had saltwater intrusion, condemn it and never plug it into an electrically clean boat. Salt water corrosion is a very rapid and dangerous cancer on stranded wire.
2. If you have warning like unexplained breaker trips, look for a problem immediately. Our problem grew quickly.
3. Understand the layout and electrical runs. Keep documentation.
4. Keep a good assortment of spares and reliable tools aboard.
5. Look for other opportunities to make your boat safer. In short order I will be adding a galvanic isolator and a 30 amp breaker within 10 feet of the shore power inlet.
6. Above all else, play it safe.

Jeff Adams
S/V Zephyrus
Bavaria Ocean 38

Posted by: SY-Zephyrus | April 15, 2018 11:50 AM    Report this comment

Like every other electrical connection on a boat, dielectric (bulb) grease prevents corrosion. A little put into the female side of the connection makes a big difference over time. The male becomes coated when inserted.

Tightening up the threaded ring lowers stress on the connection and lowers movement at the contacts.

Posted by: Boston Barry | April 15, 2018 10:28 AM    Report this comment

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