The past several years at IBEX, Metstrade and other trade shows, we’ve seen the introduction of electric devices — grills, bow thrusters, trolling motors, air conditioners and such — powered at 48 volts DC. In 2018, Integrel Solutions won a DAME Design Award for its 48-volt alternator. In 2022, Mercury Marine won a Consumer Electronics Show innovation award for its Verado V-12 outboards incorporating a 48-volt alternator. At the 2024 Annapolis Sailboat Show, six of the 16 new boats entered in Cruising World’s Boat of the Year contest had 48-volt house systems.
Suffice it to say that after years of speculation, the 48-volt boat is here. Compared with 12- or 24-volt systems, these higher-capacity systems have clear advantages: greater power, greater efficiency, less weight, lower fuel costs and, most compellingly, the potential elimination of a genset from the boat. But an emerging controversy raises questions for companies that install these systems and the people who service them: Are 48-volt systems low voltage or high voltage? The difference for safety and liability is crucial.
“Most people consider less than 60 volts low voltage, so therefore, 48-volt systems would be considered low voltage,” Bob Tate said in April at the Sur/Tech Conference hosted by the American Boat & Yacht Council. Tate is director of engineering for Navico Connect, a division of the Brunswick Group. The group’s Fathom e-Power System, which won a 2023 National Marine Manufacturers Association Innovation Award, has been installed in more than 6,000 boats and RVs. A growing number of them are designed to run at 48 volts.
But last year, the National Fire Protection Association changed its NFPA 70e Standard for Electrical Safety in the Workplace threshold for low voltage from 60 to 50 volts. The federal Occupational Safety and Health Administration follows NFPA 70e for its workplace-safety guidelines.
Accordingly, the ABYC added the concept of “safety voltage” to its 2025 supplement of “E-11 AC and DC Electrical Systems on Boats.” While the E-11 scope will remain at 60 volts DC, the supplement adds this language: “Safety voltage — an AC or DC voltage which does not exceed 50 volts DC.” That term appears several times in the new version, as in: “Ungrounded conductors exceeding the safety voltage shall have the means at wiring service points to indicate the voltage or shock potential.”
Maciej Rynkiewicz, the ABYC standards developer who oversees marine electrical standards, says it’s important to note that “48 volts DC refers to the nominal voltage. That’s a convenient, standardized engineering term used for identification and design purposes,” he says. “But the actual measured voltage of a nominal 48-volt system is typically above 50 volts.”
Tate adds: “When you have a 48-volt system, it actually sits at about 56 volts when you’re charging it. I just want to make sure everyone here realizes that OSHA thinks 48-volt nominal systems are not considered low voltage. If you’re working on a 48-volt system, it’s important for you to make a determination about what kind of protection equipment you require and how you are going to treat working with the system.”
The critical determination, Tate says, starts from the short-circuit current of the power source, which could be a charger or a DC-to-DC converter, but is almost always the battery. He highlighted a typical bank of two 24-volt lithium-ion batteries connected in series to make 48 volts. “The batteries I work on may deliver 15,000 amps of short-circuit current,” he says.
He also showed a calculation that comes to 1.91 calories per square centimeter. The NFPA threshold for requiring special PPE, such as arc-rated clothing, is 1.2 calories per square centimeter. “If you have an arc-flash event with a 56-volt system, it can jump across a fuse. The fuse is not protection,” he says.
If a company policy treats a 48-volt system as high voltage, that fundamentally changes the training and procedures for techs who work with those systems. For example, who is qualified to work on a live high-voltage system? NFPA 70e defines five formal training levels: aware, informed, competent, authorized and SR authorized. Not all of them are qualified to determine basics such as whether or not a system is live. Personal protective equipment for live high-voltage systems includes arc-rated clothing, arc-rated face shield, leather or rubber gloves, hard hat, safety glasses, hearing protection, leather footwear and insulated tools.
Tate mentioned a simple tool kit of insulated screwdrivers, pliers and socket wrenches. “That’s probably a $1,500 tool set,” he says. “And just putting some heat-shrink tubing over your screwdriver? OSHA isn’t going to accept that.”
Tate adds that another difference with these high-capacity systems is inrush current. “We have seen in 48-volt systems the contacts for battery switches or relays will be welded shut by the inrush current. They were designed in the 12- and 24-volt world, and just are not sufficient. So a device that is supposed to be able to disconnect the battery from the boat now becomes not a disconnect device at all.”
The solution Tate’s team found is to design in a system that precharges the bus before any switches or relays are closed. “Because you can’t trust the boat owner to know the proper procedure for charging the bus before they close the switch, the manual battery switch almost becomes useless,” he said.
The bottom line for manufacturers and service techs who work with 48-volt systems is that they may be different in kind from the 12- or 24-volt systems of the recent past. Before going to work on a 48-volt system, make sure to have a thorough understanding and a clear policy in place. And if 48-volt systems are new to a tech or team, call in a qualified third-party expert.
The 2025 supplement of ABYC’s E-11 standard, published July 31, will include new voltage-drop tables, including those for 48-volt systems.
For Bob Tate’s full presentation or other topics from ABYC’s Sur/Tech Conference, visit abyc.elevate.commpartners.com/products/surtech-conference-2025.
Tim Murphy is the education director for the American Boat & Yacht Council.
