Power Play: Preparing a Selene for International Shore Power (Part 1) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
By: Capt. Mark Tilden Republished by Permission from Passage Maker Magazine Shore power is an increasingly vital service for the modern cruising boat. Many boats have most, if not all, the comforts of home. But those comforts come with a nearly insatiable appetite for electrical power as well. Most larger boats have generators aboard, but running them constantly can be expensive and isn't likely to help you make friends at the dock. Fortunately, many modern (and even not-so-modern) marinas offer shore power for visiting yachts. But long before you arrive at that dream cruising port and plug in your TV, microwave, air conditioning, and laptop computer, some careful preparation for the variety of shore power standards you'll encounter will pay off. This two part article outlines the challenges of preparing a cruising powerboat for connecting to international shore power. Part 1 discusses the factors you need to consider in preparing the boat for international shore power. Then, Part 2 looks at several possible solutions and describes their advantages and disadvantages. There are four primary factors to consider in preparing for plugging in to international power:
Are you on the right frequency? Virtually all electrical power delivered by public and private utilities throughout the world is in the form of alternating current (abbreviated AC). Unlike the direct current (abbreviated DC) power that comes from our batteries, where voltage is steady and current flows in a constant direction, the voltage and current in AC power is constantly changing and alternating in direction. In the US, our AC power alternates at a rate of 60 times per second, which is called the "line frequency" and is measured in Hertz (abbreviated Hz.). However, in the majority of the world, the line frequency is 50 Hz instead of 60 Hz. While the difference between 60 Hz and 50 Hz might seem relatively minor, many types of equipment can be damaged by operating on a frequency other than the one it is designed for. Some equipment, like your water heater, will work just fine on either 50 Hz or 60 Hz power. Others will work, but may run slower or use more current on 50 Hz power. One major factor in preparing a boat's electrical system for international power is handling this frequency difference. We'll talk about several approaches to solving this problem in a moment. Getting the Voltage Right The second most important factor in preparing for international power is line voltage. There are a wide variety of voltage standards used throughout the world. The most common in the United States are 120 volts and 240 volts, though there are a few marinas that have 208 volt shore power, or higher voltages for very large yachts and commercial vessels. Differences in line voltage standards are a bit easier to compensate for than frequency differences, but they're just as critical. Mistakenly connecting your appliances or electronic equipment into incorrect voltages—either too high or too low—can cause permanent damage, and is also a potential fire hazard. It's better to be steady Another critical factor to consider is line voltage fluctuation. Line voltage standards are all expressed in "nominal" or "normal" voltage. However, if you've ever been at the outer end of a long pier full of boats in extreme weather, you know that line voltage can vary significantly with the amount of load on the wiring you share with many of your neighbors on the dock. Worse yet, in some countries, the land-based power distribution systems are not as robust or as well maintained as they typically are in the US, so even the voltage fed to the marina from the local utility can vary dramatically as load on the utility changes throughout the day. Some equipment may be fairly tolerant to line voltage fluctuations, simply shutting down without permanent damage if the voltage drops too low or blowing fuses if it gets too high. Other equipment—especially appliances with electric motors—can be severely damaged by operating on improper voltage. Equipment with motors may actually blow fuses when the voltage gets too low as those appliances tend to draw more current as the voltage falls. The amount of power an electrical device requires to do its work is expressed in watts, which is the product of volts and amps (watts = volts x amps). If a device, such as a refrigeration compressor normally uses 400 watts while running, and the line voltage falls by 20%, in order to continue to do the work, the device must now use at least 20% more current (amps) to do the same work. Unfortunately, its current flow that creates heat, so as the number of amps increases, so does the heat. Eventually, this additional heat may cause a variety of failures, from insulation breakdown in wiring to melted cases and even fires. While some devices may tolerate voltage fluctuation better than others, virtually every electrical device works better and more efficiently on a stable line voltage that is within its specifications. Plugging in Finally, physical connection requirements vary throughout the world. Most experienced cruisers end up with a locker full of adapters and shore power cords. In the US, 30 amp and 50 amp "twist lock" connectors are the most common, though new "smart plugs" that promise considerable improvements in reliability and safety are just beginning to appear on boats and marinas. In Europe, the three most common outlets are 16, 32, and 63 amp 230V circuits with European standard connectors that are commonly available. However, for many cruisers in other parts of the world, one of the high priority tasks after moving into a marina is to hunt down a local chandlery to buy adapters or bare connectors that are compatible with local shore power outlets. Some cruisers even prepare a special shore power cord with a connector for their boat on one end, and a junction box at the opposite end. When they acquire the local connector or adapter, it's easy to open the junction box and wire the new connector into their shore power cord. Of course, before connecting your boat to any unknown shore power source, you're wise to carefully verify (even measure!) the line voltage and frequency to be sure it's compatible with your on-board equipment. Also be very sure you know which are the ground and neutral conductors (if there are separate ground and neutrals). Installing an isolation transformer helps protect you and your boat from ground and neutral issues, so it's highly recommended. The table below shows a list of countries with their nominal line voltage and frequency. Where there are multiple entries for a country, it means that several different levels of shore power may be available (analogous to our 30A/120V outlets and 50A and 100A, 240V outlets). Knowing the issues is half the battle. The other half is figuring out what to do about it. There are a variety of approaches to preparing a boat to handle these issues. In the second part of this two-part article, we'll look at three general approaches to this problem and list the advantages and disadvantages of each solution.
International Power Standards
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