Even through electrical systems may vary in complexity from yacht to yacht, there are conditions that can occur in any electrical system that will almost always lead to dangerous conditions that could ultimately end up in damage to your boat, or worse, safety risks to you and your passengers. Below we’ve detailed 4 of the more common problems that can arise in just about any yacht electrical system.
1. Using Incorrectly Sized Wires Throughout Your Electrical System
When designing and implementing the wiring schematics for a yacht electrical system, the size of the wires and their insulation is one of the more important factors to consider. First and foremost, it’s important to use wires with at least 105 degree celsius insulation. Heat is produced within the wire by resistance to the current flow and the ultimate temperature of the wire is a direct correlation to the resistance. Using wires that are properly rated for higher temperatures will reduce the risk for corrosion at wire terminals, ultimately extending the life of your electrical system.
In addition to the insulation temperature rating of your wires, it’s important to ensure your wires are not buried or concealed in insulation and/or bundled too tightly together. Both the bundling of too many wires together and/or concealing wires in insulation will cause compounding of heat produced within the wires collectively, which can ultimately cause greater problems within your yacht electrical system. By ensuring the wires are not only properly rated for higher temperatures, but also ensuring they are properly stored and bundled will allow your yacht electrical system to continue running safely and efficiently.
2. Undersized or Absent Inverter and Charger DC Grounding
Inverters and battery chargers act as the bridges between a yacht’s AC and DC power systems. Within your yacht’s AC, the high voltage levels present a shock hazard and can be lethal it is not properly grounded. While the DC system is typically not a shock hazard, it can still provide a lot of current, so can still be potentially hazardous, for example in the case of fires. To avoid these situations, proper grounding must be installed between the AC and DC system.
Inverters and changers are provided with grounding connections on both the AC side and DC side. This grounding can prevent shocks from AC, and fire hazard from DC. Frequently only the AC grounding connection is made. A fault in the DC side of the system could provide enough current to overheat the AC grounding conductor without blowing the large DC fuse. Therefore, a high amperage capacity DC grounding path back to the DC system is required.
When it comes to properly wiring inverters and chargers, it is best to follow these general guidelines. The ground wire to the DC grounding system should not be smaller than one size below the wire size required for the DC current carrying conductors. The DC over-current protection device should not be sized at more than 150% of the capacity of the grounding conductor.
3. No “Green Wire” or poor-quality connection between DC negative and AC safety ground.
To avoid stray AC current from entering the DC ground system, you should ensure there is a good connection between DC negative and AC safety ground. For example, in a worst case scenario, AC current could make contact with the water around a yacht and injure or kill swimmers near the boat.
The green wire in your yacht electrical system is the safety ground wire that connects the DC negative ground block to the AC safety ground bus. This wire functions to provide a lowest-resistance path to ground for any stray AC current that finds its way onto the DC ground system.
The green wire can be tested and indicate continuity but be unable to safely carry enough current to trip a circuit breaker during a fault. There are ways to check the quality of the connection. An Ohmmeter test may show very little resistance in a green wire installation, yet the wire may be incapable of carrying 30 amperes or the higher currents needed to trip a circuit breaker during a fault. The minimum resistance reading of an Ohmmeter will not necessarily indicate if a connection is compromised, such as a connection making to only a single strand of wire. Careful visual inspection of the grounding connections helps, but even a careful surveyor may have a hard time finding all connections and tracing the wiring path.
In addition to careful visual inspection and a resistance reading, another way to test the green wire connection quality is to connect a heavy 12V load positive to the boat’s battery, and the negative to the safety ground pin of the shore cord. If all wiring is properly done, the safety ground pin should return to the battery negative after first connecting at the AC panel. If the device connected works steadily without fluctuation, there probably is a good grounding system.
4. Not Using the Shore Power Cord Locking Ring
The shore power cord locking ring creates a connection between the power cord plug and hull receptacle. When this connection is not secure, stimulus, such as motion in the water, can cause the plug to wiggle back and forth in the receptacle. Extended wiggling can cause the electrical connection to be compromised, which can result in safety issues like dangerous overheating.
Shore power connectors can have both electrical and mechanical stresses applied. The locking ring keeps the plug from backing out and fixes the two elements together so that the connection is not moved by normal motions. The constant working of the connection between shore power cord plug and receptacle with the boat’s motion can loosen the connection, increase corrosion and weaken spring contact tension.
Maintaining a safe and efficient electrical system on your yacht requires regular audits, inspections and maintenance. Regular inspections and upgrades greatly reduce your risk for electrical system failure, fires and accidental shocks or electrocutions. Contact one of our experienced yacht electricians to discuss setting up a comprehensive audit for your yacht today.
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