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Definitions Batteries Grounding
Introduction Ignition Protection References
Electrical System Regulations Wiring Page 2

Electrical Systems

Electrical regulations and standards that apply to boat builders and recreational boats.  Batteries, ignition protection, wiring.


Regulations: When referring to laws, that is, Federal Regulations or Statutes,  I will use the word Regulation and/or use a citation such as CFR 183.501, meaning Code of Federal Regulations section 183.501 or USC 4301, meaning United States Code Subchapter 4301.

Standard: Industry standards will be referred to by the name of the standard organization such as ABYC, SAE, UL or NFPA.  In most cases these standards are voluntary and not law.  However, beware! Almost all of them are the accepted practice by the industry and used by builders, marine surveyors, marine investigators, and attorneys as the de facto standard.  If you choose not to follow the standards you should be prepared to defend why your practice is as good or better. See ABYC
See Also Standards Societies.


I am only going to very briefly cover the basics of the electrical standards found in the US Federal Regulations and ABYC Standards. Contact ABYC and the Coast Guard to get the standards for Electrical systems. Canadian, European, Australian, and International (ISO) standards are very similar. Go to Ike's List to find links to these and other standards.

Ike's List
US Federal Regulations (CFR)
ABYC Standards
US Coast Guard Site for Manufacturers
Canadian Coast Guard
International Standards (ISO)


In any case you should read and use reference books on marine electrical systems. Here is a list of a few excellent books on marine electrical systems.

Boatowner's Mechanical and Electrical Manual, by Nigel Calder
The 12 Volt Bible, by Miner K Brotherton and Ed Sherman
Boating Magazine's Powerboater's Guide to Electrical Systems by Ed Sherman
Sailboat Electrical Systems, Don Casey, 1999 International Marine
Boatowner's Illustrated Handbook of Wiring, by Charlie Wing
Your Boat's Electrical System, by Conrad Miller and E. S. Maloney
Managing 12 Volts, Harold Barre 1997 Summer Breeze Publishing

If you cannot purchase them locally you can get them through Amazon or other on-line book sellers.

Ed Sherman worked for many years for ABYC teaching marine electrical systems and he has a website where he answers electrical questions.
Ed's Boat Tips

Get a copy of ABYC Electrical Systems E-11 . More Information about ABYC Standards

The US Coast Guard has guidelines on-line U. S. Coast Guard Boatbuilder's Handbook

The US Coast Guard Electrical Regulations 33 CFR Subpart I sec 183-401 - 183.460

The Canadian regulations are available on-line at TP1332 in pdf format.

There are separate regulations for commercial boats in 46 CFR Subchapter T Part 183,  but I will not discuss those here.

Electrical System Regulations:

The following are not verbatim from the regulations. It is my own wording.

First a note about the reasons behind the fuel, electrical and ventilation regulations. Why is all this stuff necessary

The Federal Regulations, 33 CFR Subpart I: 183.401 - 183.460 Electrical Systems  apply to recreational boats with permanently installed inboard gasoline engines for:



Auxiliary Equipment

This does not apply to:


Portable Equipment

Although the Federal electrical system regulations don't apply to outboard powered boats, you should use them for all boats. The industry follows the ABYC standards, which are much more comprehensive than the Federal regulations. ABYC electrical system standards apply to outboard powered boats, diesel powered boats and inboard gas powered boats. If you ever have to go to court, that's what the complainants attorney will ask you. "Do you meet ABYC standards"? So follow the ABYC electrical standards, even if you're making an outboard powered boat, sailboat, or inboard.

More Information about ABYC Standards

Canadian, ISO and RCD Regulations are very similar and embedded in laws.  Follow the laws that apply in the country where you build your boats.  See Ike's List


CFR Sec. 183.420 Batteries

Each battery must be installed so that metallic objects cannot come into contact with positive terminals. How can this be accomplished?

Battery Boxes

Boots on the positive terminal.

An insulating cover over the terminals.

There are other ways. The whole point is that you do not want a wrench or screwdriver of something metal that falls on the battery (like a metal portable gas tank) to come in contact with the positive terminal. This could cause a large arc and possibly a fire or explosion. It is best avoided.

There must be a means to vent hydrogen gas from the batteries to the atmosphere. Hydrogen gas is extremely flammable. The slightest spark will set off an explosion. Hydrogen gas discharged by a battery during charging must not be trapped in the boat, but free to make it's way out of the compartment to the atmosphere.  Make sure the battery compartment is ventilated. If you put the battery in a box, make sure the box is vented and the gas has a way to escape from the compartment where the battery is located. Hydrogen dissipates very rapidly. A simple hole in the top of the compartment will work. If the compartment has natural or powered ventilation, that satisfies the requirements.  See Ventilation:

With the proliferation of sealed batteries some people have asked, well, if the battery is sealed why do I have to ventilate the battery? Because sealed batteries might vent hydrogen. They are Sealed Valve Regulated or SVR batteries. There is a small valve in each cell that is there to vent gases if the battery overheats or overpressures. Under normal operating conditions they don't outgas, but they can.  The space that the battery is in needs to be vented.  On boats that must meet the USCG regulations it is required. 33 CFR 183.420(e)

The battery must be secured so that it can't move around. That means it can't move more than one inch forward and aft, sideways, or up and down.  A battery box will help but then the box has to be secured. Most battery boxes or trays come with a strap to hold them down. If not secured batteries can tip over, slide around, and spill acid. In one case a battery tipped over and made contact with a metal fuel tank. After the resulting discharge of electricity and fire the battery studs were welded to the tank. Batteries must be secured.  33 CFR 183.420.

If a metallic fuel line passes within one foot of the top of a battery there must be some sort of shield to keep the fuel line from making contact with the battery terminals. A battery box will achieve this, or you can place a barrier between the battery and the fuel lines.  Also if there is a fuel leak it won't drip or flow onto the battery and corrosive gases from the battery will not damage the fuel line.   33 CFR 183.420.

A battery cannot be installed directly over or under a fuel tank, fuel line fitting, or fuel filter. That's pretty obvious. Keep the battery away from fuel system components. Batteries vent corrosive gases in addition to hydrogen and these gases can damage fuel lines and other parts near the battery.   33 CFR 183.420.

Battery terminal connectors must not depend on spring tension to stay connected. Use the type of battery cables that tighten with a bolt.  Many batteries come with threaded post so the cable can be secured with a ring terminal and a nut.  The ring terminal is crimped to the wire and the nut goes on the post.   33 CFR 183.420.

ABYC standard E-11 requires that some means be provided to contain spills from the battery.  A tray under the battery or a battery box can do this.

Some people believe that the Federal Regulations or ABYC standards require a battery box.  This is not true.  It is one of the solutions that can be used and is the most common solution. But if you have other ideas that achieve the goal of securing the battery, containing spills, and preventing contact, you may use them.


 CFR Sec. 183.410 Ignition Protection

Each electrical component that is in a space where gasoline fuel fumes can accumulate must be ignition protected.

If an electrical component is in the engine room, fuel tank space, or space where there are gasoline fuel lines, then the electrical component must be ignition protected. What does ignition protected mean? It means that a spark from the device will not ignite a fuel/air mixture in the same space. In simpler words, it won't cause an explosion.

This means that alternators, generators, circuit breakers, battery switches, electric fan motors, electric fuel pumps, distributors, etc., must be ignition protected. How do you know if it is? If you buy engines from any of the major suppliers of marine engines, they come with ignition protected equipment. Make sure you buy only marine components. The automotive part may look the same but it just might kill you. Also, many marine suppliers have their parts tested by Underwriters Laboratories. Look for the UL Marine Label. If there is no label, and the manufacturer cannot satisfy you that it is ignition protected, don't buy it.

If you are marinizing or rebuilding marine engines, you must install ignition protected electrical components. So when you order be sure to specify marine parts.

Although the Federal Regulations do not apply to outboard powered boats,  ABYC standards do.  Use them for all boats. 


General:  CFR Sec. 183.425 Conductors General.

Each conductor must be insulated, stranded copper wire.

DO NOT use solid conductor, aluminum conductor, ROMEX, or anything other than a good stranded copper marine grade wire. Wiring in boats is subject to severe shock, vibration and flexing. Stranded wire is required because it is more flexible and if one or two strands break, you still have a connection. Use UL boat cable labeled UL 1426.

Some people think that only tinned wire is allowed. This is not true. Marine wire does not have to be tinned. Neither the US Coast Guard regulations or the ABYC standards require tinned wire. But tinned wire is less subject to corrosion and lasts longer.  Many marine professionals insist on using only tinned  wire. It is more expensive than un-tinned wire.  But boat wire must be marine wire whether it is tinned or not.

In addition to the regulations, ABYC Standard E-11 says:

*Each conductor or group of conductors must be supported by clamps or straps not more than 18 inches apart. or:

*The conductor or group of conductors may be enclosed in a rigid duct or conduit.

*The clamps or straps must not chafe or abrade the conductors.

*The above three rules are not Federal Regulations, they are ABYC standards. In fact they were part of the Federal Regulations until the mid 1980's when the Coast Guard took them out of the regulations to comply with the Reagan administration's policy on deregulation. They took them out because they were in the industry standard and most professionals were doing it anyway. However,  they are good  practice when installing wiring.  Wiring should not be just snaked through the boat.  You want it to be neat and run in bundles so it is easily traced, and easily replaced.  Plus, it protects the wire against vibration and shock.  You don't want it getting in the way of access to the engine or other components so give some thought to how it is routed and secured in place. You may use more wire this way but it makes a much better, safer installation.

DSCF0023a.jpg (65476 bytes) This is a nice neat electrical layout with a charger and a battery switch.

Good Practices: 

DO NOT just hang the wire through the boat. Support it. You don't want the wiring moving around, swaying back and forth, and loose in the boat. This is dangerous. It will cause the wiring to fatigue and break, and chafe against other parts of the boat.

DO NOT use staples. Don't staple the wire to bulkheads and stringers. The metal staples cut through the insulation. They create a HARD SPOT. That's a point where stress is concentrated. That's where the wire breaks.

DO USE good marine grade clamps or straps to hold the wire in place, or use conduit or wire loom.  However, if you use wire loom use wire loom that is self-extinguishing. 

Low Voltage Wiring: Less than 50 volts  CFR Sec. 183.430.

Low voltage conductors must comply with SAE standard J1127 and J1128 and the insulation temperature rating of SAE J378b or UL standard 1426.

Look at the labeling on the wire. Does it say UL Marine? Does it have an SAE or ISO rating? If there is no label on the wire is the spool or package labeled? Many wire manufacturers don't label the wire but they do label the package it comes in.

Good Practices:

DO NOT use wire that has no labeling on the wire or on the spool or packaging.

DO NOT go to your local auto store and buy automotive wiring off the shelf! Get your wire from a marine supply. Ask them if it is labeled and what the label says.

DO NOT USE ROMEX. (triplex house wire)


High Voltage Wiring: 50 Volts or more. CFR Sec. 183.435.

High voltage wires have specific requirements as well. They must meet one of the following requirements:

(1) A conductor that has insulation listed and classified moisture resistant and flame retardant in Article 310, NFPA No. 70, National Electric Code;

(2) A flexible cord type SO, STO, ST, SJO, SJT, or SJTO listed in Article 400, NFPA No. 70, National Electric Code;

(3) A conductor that meets IEEE Standard 45.

(4) A conductor that meets UL Standard 1426.

If it meets one of the above it can be used in high voltage circuits.  The most commonly used wire is UL 1426 boat cable.  For 120 Volt AC systems the recommended wire is UL Boat Cable triplex wire. On the outside this looks just like triplex wire used in houses. Look at the labels on the wire.  It should say UL 1426 or UL Boat Cable.


Where the nominal circuit voltage of each of three or more current carrying conductors in a duct, bundle, or cable is 50 volts or more, the amperages of each of those conductors must not exceed the value in table 1 multiplied by the correction factor in note 2 to Table 1 for the number of conductors that carry 50 volts or more. Table 1:

What that means, is that wires in a bundle or in ducting can handle less current than single wires. See the notes on the table.  Table of Allowable Amperage of Conductors

Exceptions: This section does not apply to communication systems; electronic navigation equipment; resistance conductors that control circuit amperage; conductors in secondary circuits of ignition systems; and pigtails of less than seven inches of exposed length.  So the above does not apply to the wiring inside your radios, GPS, radars or to the ignition wires on the engine. 

These wires are enclosed inside the equipment, and many appliances have built in circuit protection for the device. So they have some protection in case of overheating.


CFR Sec. 183.415
On twin engine gasoline inboards there must be a ground connection for the starting (Cranking) motor and there must be a connection between the starting motors for each of the two engines.
  This should be the same gage wire as the wire from the battery to the starter.  The reason for this is simple. If there is a fault, all the current flows through the ground wire. If there is no ground wire it will burn up the electrical system on the engine and may start a fire. ABYC requires this on all twin inboards,  outboards and diesels. 
See Grounding and Bonding: Basic Electrical Practices
See also grounding of the boat's fuel system:

There is more on Page 2


ABYC Electrical Systems E-11

More Information about ABYC Standards.

USA 33 CFR Subpart I: Electrical Systems

Canadian Coast Guard Standards for small craft.

ISO Standard 13297: Small craft — Electrical systems — Alternating and Direct Current systems installations

46 CFR Subchapter T Part 183 Electrical Installations: Passenger Vessels under 100 Gross Tons .  USA Standards for Commercial Small Passenger Vessels.

Continued on Page 2 >>

Page 2, Amperage Table on Page 3, Wire Size Pg 4

Copyright 2010 All rights reserved.  revised 04/28/2021

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