AC System


Breakers & Fuses – AC System
  • See ‘Wiring‘ project page.
Dock Cord
  • The size of the extension cord from the AC outlet on the dock to the receptacle on your boat depends on the amount of juice you need. Most boats in the 30 – 40’ range use 30-amp wire, though some opt for the larger 50-amp. Good quality connectors…should be used on either end  (Upgrading the Cruising Sailboat, p. 280)
  • The nature of a shore-power cord is such that it has plugs at both ends. Connections using plugs are not as reliable as bolted connections. If either plug makes a poor fit or has corroded pins or sockets, resistance will be created, which then creates heat – the great the current flow, the more heat. The resistance may also result in arcing. In both cases (heat and arching), the end result may be a fire for which the various over-current devices in the circuit provide no protection. The higher the current flow, the greater is the probability of a fire. These kinds of fires are not that uncommon, particularly with AC-loaded boats, so be warned and pay close attention to the condition of shore-power cords and inlets: replace any that have corroded, pitted, or blackened pins or sockets.  (Cruising Handbook, p. 187)
Outlet & Inlet Fittings
  • Outlets – AC outlets are all polarized….White goes with silver, so the black wire, the hot one, connects to the opposite terminal, usually brass but sometimes dark. The green terminal is fore the green grounding wire…do not loop the stripped wire end under the terminal screws on boat outlets. Also the spring-clip attachments found on lots of outlets are for solid wire, which you are not using. Commercial-grade outlets with screw-tightened clamps are a good choice and you can attach stripped wire ends directly to them. Otherwise crimp ring terminals to the ends, or locking spade terminals if the terminal screws in the outlet are captive.  (This Old Boat, p. 307)
  • Inlet Fitting – the inlet on your boat should be weather tight when connected and when disconnect. Screw-on caps are more secure than those sealed with spring pressure. A high-quality bronze or stainless steel fitting costs only a few dollars more than the plastic variety, but should last the life of the boat. Located the inlet where it is convenient but safely out of the way. Mount it as high as possible The backside of the inlet should be well ventilated and not at risk of mechanical damage.  (Sailboat Electrics Simplified, p. 144)
  • Because the 30 amp locking receptacle has become the norm at most North American and Caribbean marinas, configuring your AC system for 30 amps avoids the compatibility problems that will plague you if you arrive with a straight-blade 15 amp cord. The power cord is the first in the train of components to safely power AC appliances board…From the dock to the boat you need a power cord rated for the amperage of the dock outlet (#10 AWG or larger for 30 amp service) and carrying a hard-service rating of SO, ST, or STO to withstand submersion, abrasion, exposure, and strain.  (This Old Boat, p. 306)
  • The boat end of your cord should attach with a sealing collar to weatherproof the inlet…should be located as high on your boat as is practical and not more than 10 feet (wire distance) from the boat’s main AC circuit breaker. This wire, protected only by the 30 amp breaker ashore, must also be at least #10 AWG.  (This Old Boat, p. 306)
  • Without air conditioning, a single 30-amp inlet is almost always adequate. If air conditioning is installed, a single 50-amp inlet generally handles the boat’s entire AC load; however I recommend separating out the air conditioner and having two independent 30-amp inlets – one running the air conditioner and the other the rest of the boat’s AC circuits. Although the two independent 30-amp circuits create a modest increase in complexity over a single 50-amp inlets, there are two good reasons for this approach: 1) cost, weight, and ease of use – 30 amp shore power cords are well under 1/2 the price, 1/2 the weight, and 1/2 the bulk of same-length 50-amp cord 2) flexibility – with three or four adapters, a 30-amp cord can be plugged in just about anywhere. These adapters are also much cheaper than adapters for 50-amp cords. For times when only one 30amp inlet is available, the boat’s AC selector switch can be configured to line up one o the inlets with all the boat’s C circuits. The shore-power cord cannot support all the loads at once, but at least the boat owner can determine which ones to use.  (Cruising Handbook, p. 189)
  • The female receptacle should be located somewhere on deck where it is relatively free from spray and other sources of moisture. A common location is on the side of the footwell, perhaps near the after end of the cockpit.  (Upgrading the Cruising Sailboat, p. 280)
  • Regarding a shore power connection, the choice (in the US) is between a 30- and a 50-amp inlet (in Europe, it is commonly 16 amps or less).  (Cruising Handbook, p. 189)
  • See ‘Wiring‘ project page

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