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Understanding Electrical Safety
Larry Budd, applications engineer at Charles Industries’ Marine & Industrial Group, explains how to make safe use of AC shore power.
LB: We rely on shoreside grounding lines to protect against electrical fires and shock accidents. Why do these hazards still exist in marinas? Budd: Most marina safety grounds are far from the individual slips, and the shore power cables that connect vessels to dockside power are often in poor condition, with connections not properly protected. Waterside junction boxes and outlets corrode, and if either path to ground isn’t up to snuff, a short or fault may fail to push enough juice back up the line to trip a breaker. Instead, the fault area will heat up, possibly causing a fire. Worse, the current flowing into the boat may seek another route home through the adjacent water toward land. It doesn’t take much of a leak, especially in less conductive fresh water, to seriously injure or kill a human being. Hence the need for “No Swimming” signs in marinas. LB: What’s the best solution? Budd: Onboard isolation provided by an isolation transformer eliminates the risk of leaking electricity to or from the surrounding water. The transformer has no mechanical connection from the input to the output. Instead, a magnetic connection from input to output is created. Simply put, you electrically float your boat, meaning the boat’s electrical power source is no longer shore power; instead it’s the onboard transformer’s output. Onboard AC faults are prevented from inducing stray current into the water around the vessel; instead, they return to the transformer’s output. LB: Aside from safety, are there other advantages to an isolation transformer? Budd: Being isolated from a marina and other boats means your onboard AC power will be cleaner, unaffected by any other unprotected vessels’ electrical noise that might otherwise be spreading interference to you boat’s onboard circuits and equipment (i.e. buzz in the VHF). In cases where dockside shore power voltage is low, an isolation transformer with boosting capability will allow other onboard AC electrical equipment to operate with the proper rated input voltage, protecting it from damage and extending its service life. PHOTO COURTESY OF CHARLES INDUSTRIES
LB: Is the isolation transformer susceptible to a lightning strike? Budd: Charles isolation transformers are Marine UL listed and unique in that they are designed with a full current carrying shield (E-11) and high-grade insulation. Isolation transformers of this design are capable of withstanding a nearby lightening strike without adversely affecting the boat’s AC electrical system. LB: How does one determine the size of isolation transformer needed? Budd: Typically, they are sized in correlation to the vessel’s AC input shore power. With current (I) and input voltage (E), I x E/1,000 provides the size in KVA (Kilovolt amperes) of isolation transformer required. LB: Where are isolation transformers typically installed? Budd: Mounting location typically depends on the size of the vessel and the size of the isolation transformer. Weight of the unit is also a consideration, so as to ensure the vessel sits balanced in the water. Isolation transformers should follow manufacturer installation instructions and be securely mounted to a solid surface within 10 feet of the vessel’s shore power breaker(s).
CONTACT Charles Industries Ltd. Marine & Industrial Group 5600 Apollo Dr. Rolling Meadows, IL 60008 847-806-6300 lbudd@charlesindustries.com charlesindustries.com
LB: Is there a bad side to using an isolation transformer? Budd: They can be heavy, 15 to 20 pounds per KVA heavy. They’re extremely dense square cubes, ranging in size from an approximate 10” X 10” cube, up to a 24” X 24” cube. Planning ahead for aftermarket installation is essential. Often, Charles works directly with customers to offer advice on product selection and installation. Founded in 1968, Charles Industries provides innovative products and services to telecommunications, municipality, utility, marine and industrial markets worldwide. The company proudly supports “Buy American” initiatives. 83 LAKELANDBOATING.COM O C T O B E R 2 011