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A Step-by-Step Approach to the Design of an AC or DC Marine Electrical System

One of the questions most frequently asked by boat owners during visits to our boat show booths over the years is “How do I go about designing a safe, compliant marine AC or DC electrical system that will meet all of my present and future power requirements?” Unfortunately, there is no simple answer to this question. However, after 25 years of listening attentively to customers, we have developed the following useful step-by-step approach to marine AC and DC electrical system design.

The marine industry is fortunate to have a boating standard organization. The American Boat and Yacht Council or ABYC is a consortium of boaters, marine surveyors, boat manufacturers, and the U.S. Coast Guard, working together to establish marine safety standards and recommended practices. Paneltronics is proud to have direct involvement in ABYC electrical standards development. Since 1988, we have actively participated in the ABYC Electrical Project Technical Committee. We design and manufacture our products to comply with ABYC standards, and we encourage you, as a potential customer, to do the same. Since we will be referring to ABYC Standard E-11, *AC and DC Electrical Systems on Boats throughout this text, you should obtain a copy. Excerpts from ABYC E-11 can be found here.


Step 1 - Safety First:

Although every Paneltronics panel is completely pre-wired for ease of installation, we recommend that if you are not comfortable working with electricity and you want to avoid possible exposure to shock or electrocution, hire a qualified and experienced marine electrician. An ABYC Certified Marine Technician would be a great place to start. For a list of certified technicians, visit the ABYC web- site at, go to Certified Technicians and follow the screen directions.

A safety issue that must not be overlooked is fire. In an article “Why Boats Catch Fire,” published in the July 2003 issue of Seaworthy magazine, a Boat U.S. Marine Insurance claim study revealed that 55% of all boat fires start onboard vessels in the AC or DC wire harness, or in related appliances. Once ignited, electrical fires are difficult to extinguish unless the fault can be isolated from the power source since the heat generated from shorted wiring can re-ignite a totally extinguished fire. To minimize the possibility of damage, injury, or loss of life caused by boat electrical fires, you must design your electrical system to both isolate and limit the current in each appliance circuit. Obviously, the related costs required to isolate individual circuits in marine electrical systems will be greater than those incurred for similar residential wiring. The justification for this additional margin of safety on boats is that an open window or door can provide an easy escape from a burning house, but walk- ing away from a burning boat may not be an option. By isolating individual circuits, there is a greater likelihood that critical electrical appliances will function during a fire emergency.

Overcurrent Protection:

It is our view that the magnetic circuit breaker is presently the most reliable and cost-effective device for use in the marine environment to isolate and limit the current in an individual appliance circuit. Although it is common practice to use single rating circuit breakers (i.e. 15 Amps) for all loads, this may, at best, provide only conductor (wire) protection. Proper circuit breaker selection and sizing is critical. By selecting the proper amperage rating for each load (ABYC E-, both the conductor and the individual appliance connected in the circuit will be isolated and current limited.

Step 2 - Load Calculation:

Before considering battery ratings, generator outputs, or wire gauges, you should first establish the total AC and/or DC requirements for your electrical system. For DC systems, refer to ABYC E- and complete Table II. For AC systems, see ABYC E-11.8.2 and complete all the sections through E- Remember to plan for future expansion. The addition of spare circuits now will save you considerable time and money in the future. Once you have determined your power requirements, you can then consider power source options.

Step 3 - DC System:

The most widely used DC power source is the battery. Other sources of DC power include solar panels, wind generators, and alternators, but for the purpose of this article, we will only concentrate on batteries. The most popular DC voltage rating found on vessels is 12VDC, although 24VDC and 32VDC are also popular ratings on larger boats. Paneltronics offers DC panels in 12VDC, 24VDC, and 32VDC.

Engine Starting Batteries:

Engine cranking batteries are similar in construction and function to automotive batteries, but the materials used in automotive batteries will limit their longevity in a marine environment. Engine cranking batteries are designed to deliver a short burst of power, followed by a quick recharge. The Marine Engine General Data Sheet supplied by the engine manufacturer will specify the minimum Cold Cranking Ampere (CCA) battery rating required to ensure a reliable engine start (see ABYC E-11.4.3 DEFINITIONS Battery cold cranking performance and ABYC E-

House Batteries:

Unlike cranking batteries, house batteries are constructed with thick lead plates designed to be discharged over a long period of time. They may be discharged to about 50% of their capacity, and then recharged. These deep cycle batteries, so called because of this characteristic, are the batteries of choice for running appliances during long cruises. To select the proper rating for your deep cycle batteries, first, refer to Table II in Step 2, and expand the data by multiplying each appliance load current (in amps) by the number of hours you plan to operate the appliance (in a 24 hour period). The sum of these amp-hour requirements represents Part 1 of the total DC Daily Load. Part 2 is calculated if an optional inverter is installed on your AC system, and is explained in the inverter section later in this article.

With the exception of cranking motor circuits, please note that overcurrent protection is required in all conductors connected directly to the batteries. (See ABYC E- and FIGURE 15 for placement requirements). It is important to remember that overcurrent devices placed in fume areas must also be ignition protected (ABYC E-

Step 4 - AC System:

AC represents Alternating Current. In marine electrical systems, the most common sources for alternating current (AC) are shore power from utility company generators, onboard generators, and inverters.

Shore Power:

In the United States, the 3 most readily available marine shore cord configurations are 120VAC- 30 Amps, 120VAC- 50 Amps, and 240VAC- 50 Amps (ABYC E- through E- AC shore cord systems rated at 220VAC- 50Hz are commonly used in Europe and other parts of the world. Paneltronics offers panels for all these electrical systems, including panels with circuit breakers having the required European CE approval. When selecting shore power cords, check the quantity and ampacity of the inlets available on the dockside stanchions where your vessel will be docked. Then evaluate the physical weight and cost of each available shore power cord set that will power the maximum number of AC loads calculated in Step 2 above (ABYC E- through ABYC E-

Shore Power (Continued):

Leakage Currents caused by defective wiring or defective electric appliance onboard a vessel present a significant shock hazard to personnel. In order to significantly reduce the risk of electric shock hazard to personnel in the water near a vessel, boarding a vessel, or onboard a vessel that is connected to shore power, effective July 2009 each 120VAC 60Hz or 240VAC 60Hz shore power cord set, or feed, must be protected by an Equipment Leakage Circuit Interrupter (ELCI) (see ABYC E-11.11.1). The ELCI may be a stand-alone device or part of the Main Shore Power Disconnect Circuit Breaker located on the AC distribution panel.

If the distance from the shore power inlet mounted on the vessel is greater than 10 feet, measured along the conductor from the location of the Main Shore Power Disconnect Circuit Breaker, an additional overcurrent protection device and the ELCI is required within 10 feet of the power inlet (ABYC E- through E- ELCI devices installed in fume areas must be mounted in enclosures that are “Ignition Protected” (ABYC E- and ABYC E-11.4.15). In addition, ELCI devices mount- ed in locations subject to rain, spray, or splash must be weatherproof (ABYC E-11.4.31).

Another dangerous condition that can create a shock hazard for personnel in the water near a vessel, boarding a vessel, or onboard a vessel is a Reverse Polarity. This is the unintentional backward connection of the hot (ungrounded/black), the neutral (grounded/ white), or grounding (grounded/green) AC shore conductors. ABYC requires that a visible indicator of reverse polarity be present near the AC shore main circuit breaker (ABYC E- As an additional safety feature, Paneltronics provides an AC Shore Main Circuit Breaker that includes a Reverse Polarity trip coil. This “smart” circuit breaker trips automatically upon sensing a potentially dangerous reverse polarity condition.

It is our opinion that the installation of Isolation Transformers should be considered for all shore power circuits (ABYC E-11.7.1). They are designed to prevent galvanic corrosion and the hazard of electric shock caused by reverse polarity in the dockside stanchion. Personnel who are boarding, onboard, or swimming in close proximity to an unprotected vessel connected to an improperly wired dockside stanchion are exposed to potentially lethal electric shocks. Properly installed, isolation transformers magnetically couple a vessel’s AC system to shore, and at the same time, they isolate shore ground from the floating grounded neutral AC system onboard the vessel (ABYC E-11.17.4) and (ABYC E-11.17.5).

Note: Isolation Transformers should be mounted on a non-conductive surface. Mounting hardware should not come in contact with any vessel metallic structural members. Finally, to ensure that total isolation from shore ground is maintained, ground connections from telephone lines and cable TV must also be isolated by transformers.

AC Generators:

Generators are machines for generating AC electricity. To determine the size of the proper AC generator required for your application, multiply the total AC load calculated in amperes in Step 2 above (see ABYC E- by the AC system voltage, and divide by 1000. This result is the minimum KVA generator output rating required for a single-phase system (ABYC E-

Note: The AC system onboard vessel is a polarized grounded neutral system (ABYC E-, (ABYC E-, and (ABYC E-; therefore, the generator neutral must be grounded at the generator (ABYC E-

Observance of the 7/40-inch rule for the placement of overcurrent protection devices may require their placement within a gasoline fume area near engines or generators (ABYC E-, (E-, and (ABYC E-11.4.15 DEFINITIONS Ignition protection). These overcurrent protection devices must be ignition protected. Paneltronics manufacturers circuit breaker panels with ignition protected (UL 1500) two-pole C-Frame circuit breakers that will bring your generator installation into compliance (ABYC E-


Inverters are devices that convert DC battery power to Alternating Current (AC) for powering household appliances. These devices are very popular on smaller boats, or as back-up to generators. Larger inverters may be used in place of generators. Inverter advantages include quiet, pollution-free AC power on demand. However, larger inverters require larger battery banks to sustain their operation.

Note: Inverters are a major consumer of stored DC battery power. Consider this when calculating your total battery requirements. To determine the battery requirements for an inverter, use this simple calculation. Multiply each AC appliance power rating in watts by the number of hours you plan to operate the device for a 24 hour period (watt-hours); then add the sum of all AC appliances powered by the inverter and divide by the DC system voltage (12, 24, or 32VDC). This total should be added to Part 1 of your previous DC calculations for Daily Load. Finally, multiply 4 (diversity factor) to obtain the total Amp-hour rating of the required battery bank.

Single Power Source Selection:

Cogeneration, powering a load by multiple power sources at the same time, does not presently meet ABYC standards (ABYC E- Therefore, single source selection that isolates all power sources must be assured with the use of a break before make switch or lockout device (ABYC E- Paneltronics panels offer these for safe selection of up to 6 power sources (i.e. shore power, generators, or inverters) (ABYC E-

Wire Sizing:

The construction of insulated conductors (wire) used in marine AC and DC systems is very different. Conductors approved for AC use may also be used for DC, but the converse is not true. The insulation temperature rating of most marine wire available today, AC or DC, is 105°C. By selecting 105°C rated insulated wire opposed to 75°C rated wire, higher currents can be transmitted safely using thinner, lighter wire. The markings on individual marine wire conductors must include type/style, voltage rating, gauge, and temperature rating (ABYC E- The minimum wire size permitted for marine use is 16 American Wire Gauge (AWG); however, there are several exceptions (see ABYC E- The possibility of strain hardening caused by low-frequency vibration present on vessels mandates the exclusive use of stranded copper wire (ABYC E- and ABYC E- Tinned, stranded copper wire is the preferred wire conductor for use in marine electrical systems because it offers maximum protection against corrosion. At junctions, this wire is galvanically compatible with tin-plated terminals. This compatibility helps prevent high resistance connections, overheated junctions, and fires.

DC Wire:

DC wire must have a minimum 50-volt insulation rating (ABYC E-, and this insulation must meet the temperature rating requirements of the Society of Automotive Engineers (SAE) J378 and SAE J1127, or J1128 (ABYC E- through ABYC E- Wire types that conform to these requirements, such as GPT (PVC marine engine and component wire) and Boat Cable (UL 1426), are readily available. To calculate conductor size, see ABYC E- through ABYC E-

AC Wire:

AC wire must have a minimum 600-volt insulation rating (ABYC E-, and flexible cords must have a minimum 300-volt insulation rating (ABYC E- This insulation must also meet the flame retardant and moisture resistant requirements of UL 83 (ABYC E- Wire types that conform to these requirements, such as AWM 1230, AWM 1231, and Boat Cable (UL 1426), are also readily available. To calculate conductor size, see ABYC E-11 AP TABLE 1 and ABYC E- through ABYC E-

AC and DC Power Distribution Panels:

The primary considerations in the selection of an AC or DC power distribution panel are DESIGN, QUALITY, FUNCTION, and STYLE. Although many panels appear to be similar, close inspection may show practical and functional differences.

Design Elements to be considered:

Functional Elements to be considered:

Quality features to look for:

By now you should have determined the total number of circuit breakers, the ampacity for each load, and all of your power inputs. In addition, you should have considered the design, function and quality elements that you want to incorporate in your panel. By coupling this information with the physical size available for your installation, you should be able to select the proper AC and/or DC power distribution panel. Paneltronics offers you over 180 modular panel designs. Each model is pre-wired for a simple installation. For additional product information, please visit us online at www. or call us toll-free at 1-800-36-PANEL. Factory trained technicians are available to help you design a safe, compliant marine AC or DC electrical panel system that will meet all of your present and future power requirements.

A Technical White Paper Equipment Leakage Circuit Interrupter (ELCI)


This document is provided for information purposes only. Paneltronics, Inc. makes no claims, promises, or guarantees about the accuracy, completeness, or adequacy of the information contained in this white paper, and disclaims all liability concerning the information and/or the consequences of acting on any such information. Performance of the products referenced herein is exclusively subject to the applicable manufacturer’s terms and conditions of sale. Nothing stated in this white paper constitutes the establishment of any additional agreement or binding obligation between Paneltronics, Inc. and any third party.

ABYC Requirements

ABYC E-11.11.1 An Equipment Leakage Circuit Interrupter (ELCI) shall be installed with or in addition to the main shore power disconnect circuit breaker(s) or at the additional overcurrent protection as required by E-, whichever is closer to the shore power connection.

ABYC E- This device shall meet the requirements of UL1053 Standard for Safety for Ground Fault Sensing Relaying equipment and the requirements of UL 943 Ground Fault Circuit Interrupters with the exception of trip level and trip time. Trip level shall be a maximum of 30mA. The trip time shall be a maximum of 100ms.

Note: Trip levels of less than 30mA and trip times less than 100ms may result in nuisance trips in certain environments.

ABYC E- The ELCI shall be readily accessible

ABYC E- Additional Overcurrent Protection - If the location of the main shore power disconnect circuit breaker is in excess of 10 feet (three meters) from the shore power inlet or the electrical attachment point of a permanently installed shore power cord, additional fuses or circuit breakers shall be provided within 10 feet (three meters) of the inlet or attachment point to the electrical system of the boat. Measurement is made along the conductors.

Implementation of ABYC E-11.11.1 is required for all new shore power installations beginning July 31st, 2010. To obtain the latest information about the implementation of E-11.11.1, go to ABYC’s web site @, or contact John Adey, ABYC’s Technical Director, at 410-990-4460.

Executive Summary

Utilizing a Coast Guard grant, ABYC conducted multiple tests to evaluate in-water shock scenarios and possible mitigation devices. Based on that data, ABYC has established a requirement for the aforementioned ELCI and has designated July 31st, 2010, as its implementation date.

In order to comply with the new standard, all 120VAC 60 Hz and 240VAC 60 Hz shore power installations are required to be equipped with an Equipment Leakage Circuit Interrupter (ELCI).

There are several manufacturers of these devices that have either launched or will soon launch production parts for 120VAC/ 30A, 120VAC/ 50A, 240VAC/ 50A, and 240VAC/100A applications that will comply with the requirements of ABYC E- 11.11.1.

Implementation of this ELCI device will require OEM boat builders to initiate one of two courses of action; include it as an integral part of the AC electrical system for each shore power line installed onboard, or provide an in-line solution for each shore power line.

There are pros and cons to each solution which will need to be weighed by the OEM.

ELCI Purpose

To reduce the risk of possible injury or electrocution to persons swimming in close proximity to vessels connected to shore power, as well as persons on board a vessel and persons on shore who are in contact with a vessel’s bonding system in the event of an AC leakage fault current.

The ELCI is a residual current device (RCD) which detects equipment ground fault leakage current and disconnects the current carrying conductors at a maximum trip level of 30mA with a maximum trip time of 100ms.

In 120VAC 60Hz systems the ELCI/Breaker combination disconnects the Hot (ungrounded / black) and the Neutral (grounded / white) conductors, while in a 240VAC 60Hz system, the ELCI disconnects both the Hot #1 (ungrounded/black) and Hot #2 (ungrounded/red) current carrying conductors. An alternate 240VAC 60Hz

ELCI Rationale and History

Here in the U.S.A., the only requirement up to this point has been for a GFCI having a trip level of 5mA and 25ms to be located in galleys, heads, machinery spaces and weather decks (ABYC E-11.13.5)

The ELCI can actually trace its roots back to Europe. During 1994, the International Organization for Standardization (ISO) began developing standard ISO 13297 to regulate the installation of electrical systems in small craft. One of its directives, ISO 13297.8, focused on the potential danger to people from an electrical shock hazard from vessels connected to 220 VAC 50Hz shore power.

A Ground Fault Circuit Interrupter (GFCI)/ residual current device (RCD) having a maximum sensitivity of 30mA @ 100ms was required to be installed on board in each main shore power supply line. As an alternative, an RCD having a maximum sensitivity of 10mA @ 100ms is required in certain spaces such as galleys, heads, machinery spaces, and weather decks.

As one can plainly see, the trip levels of the ISO required GFCI/ RCD and that of an ABYC UL 1053 Listed GFCI are significantly different. The intention of the US-based GFCI was to protect receptacles where portable appliances located in wet areas are plugged in. The intention of the ISO based GFCI/ RCD was to protect the whole vessel from a ground fault or to protect receptacles where portable appliances located in wet areas are plugged in. However, both devices sense the difference in the current flow in the Hot and Neutral lines. If this differential current exceeds the preset trip threshold, the device opens both conductors.

It is important to note that this differential current is a short circuit current or ground fault current caused by the failure of insulation in the boat’s wiring, in onboard loads, or in onboard sources of power. Because the current level of this ground fault current may be in the milliamp range, no conventional main or branch circuit breaker onboard will trip. However, ground fault currents can prove to be a shock hazard; fortunately, the RCD fills this safety gap in European 220VAC 50Hz systems.

In the event of the absence of ground in the dockside power pedestal; a poor quality ground connection at the power pedestal caused by corrosion or improper installation; improper shoreline connector maintenance; or an open ground conductor in any part of the AC shore power system, the RCD will still open both current carrying conductors in the event of a detected ground fault current.

In addition to the existing ISO requirement that an RCD be installed onboard for each main shore power supply line, each dockside power pedestal line must also be equipped with an RCD. At the present time, there is no provision in the NFPA- 303-2006, the marina safety standard, to mandate the use of ELCI devices in US dockside power pedestals. There is a provision for an optional power pedestal mounted GFCI, but the GFCIs 5mA and 25ms trip point will undoubtedly cause nuisance trips (ABYC E- Note)

During the summer of 2007, funded by a grant from the United States Coast Guard, ABYC conducted tests on Lake Meade (a freshwater lake) in Colorado and fourteen other locations to determine a safe trip point for 120VAC 60Hz and 240VAC 60Hz ELCI devices. Utilizing ELCI test devices supplied by Sensata Technologies and North Shore Safety, Ltd., the same RCD 30mA and 100ms maximum trip levels were established for the 60Hz ELCI devices. Therefore, in the not too distant future, RCDs that have been tested to UL 1053 and UL 943 FTTJ2 can then be considered a qualified ELCI device that will comply with ABYC E- 11.11.1.

The result of this exercise was the ABYC requirement for an ELCI device to be installed in each shore power line.

The International Marine Certification Institute has recently validated the ELCI as defined in ABYC E-11.11.1 as an acceptable replacement for the RCD device now utilized in Europe. However, international versions of the ELCI must be compliant with European 220V 50Hz power systems. In addition, ELCI RCBO devices must also comply with European 16A, 32A, or 63A shore power cord sets. Also, if an international version of the ELCI is located in a fume area, testing to the ISO 8846 Standard (Small craft- Electrical devices-Protection against ignition of surrounding flammable gases) will also be required. Although at the present time, there is no European standard for RCD construction within ISO 13297 (Small craft-Electrical

systems-Alternating current installations), the international ELCI should have the CE mark.

Current Solutions

Today, compliant ELCI devices are available in three basic configurations:

  1. The ELCI/RCBO which combines overcurrent protection and leakage current protection in a single compact economical package;
  2. The ELCI/RCD sensing module coupled with a separate compliant magnetic circuit breaker that provides overcurrent and leakage current protection;
  3. The ELCI/RCD sensing module coupled with acompliant contactor that provides only leakage current protection.

Manufacturer’s recommendations

Similar to a GFCI, the ELCI must be tested on a regular basis by depressing the Test and Reset Buttons mounted on the front of the device, and the LED indicators or toggle switch handle must be visible to determine the system status (Power On or Fault Condition). This is supported by the ABYC requirement for the device to be readily accessible (ABYC E-

In addition, the mounting location of each ELCI device establishes a specific set of environmental and electrical requirements that must be satisfied in order to be compliant.

  1. Units mounted in engine rooms must be rate data maximum operating temperature of 85°C to allow a 35°C rise above the 50°C engine room ambient temperature to comply with ABYC E-11.5.1.
  2. Units mounted in fume areas must be Ignition Protected and tested to UL 1500 or SAE J1171 to comply with ABYC E-
  3. Units mounted in wet areas must be watertight to comply with E- 11.4.30.
  4. ELCI compliant circuit breakers must meet the requirements of UL 489 or UL 1077 and be trip-free; manually reset, and have an interrupting capacity of 3,000 Amps for 120VAC 30 Amp or 50 Amp systems; and 5,000 Amps for 240VAC 50 and 100 Amp systems per ABYC E-11.10.2.

Wiring requirements

At this time, most ELCI sensing modules utilize toroidal sensors. The inside diameter of this sensor will restrict the maximum diameter of the cable type used.

Click the image above to enlarge.

Code Key:

a. All ELCI RCBO and RCD devices (comprised of an ELCI Sensing Module and an ELCI Compliant Circuit Breaker) have a single operating handle.

b. ELCI Form Factor A-Frame RCBO and RCD devices have a maximum overcurrent rating of 30 amps.

c. To prevent nuisance overcurrent tripping at the shore power inlet, ELCI RCBO and RCD devices with Long Delays are best suited to be mounted at the shore power inlet.

d. ELCI RCBO and RCD devices with Medium Delays are best suited to be mounted on or at the main distribution panel.

e. ELCI RCBO and RCD devices are tested to meet the requirements of ABYC E-; however, today’s restrictions on the marking of ELCI devices set by Underwriters Laboratories will cause UL compliance marking to vary by configuration and manufacturer.

ELCI RCD Sensing Modules that utilize an external toroidal transformer today may not be marked UL Listed or ЯU Recognized because UL considers that these devices require field assembly, and UL 943 does not today have a designation for an ELCI device. Additional markings may include a statement indicating compliance with ABYC E-, a statement that the product meets the requirements of UL 1053, UL 943, UL 943 Category FTTJ2, and the name of an independent testing laboratory,

ELCI RCD Compliant Circuit Breakers that today meet the requirements of UL 489 are marked UL Listed, or if they meet the requirements of UL 1077 Recognized they are marked ЯU (ABYC E-

ELCI RCBO devices that utilize external toroidal transformers today may not be marked UL Listed or ЯU Recognized because UL considers that these devices require field assembly, and UL 943 does not today have a designation for an ELCI device. However, a specific ELCI RCBO manufacturer utilizing a UL 943 compliant sensing device and UL 489 constructed circuit breaker has received permission to mark their ELCI RCBO device ЯU Recognized.

f. Because the ELCI is not a combination outlet and GFCI device, no end of life indicator is required by the UL Standards.

g. Does not provide an indicator to distinguish between leakage current and overcurrent trips h. Does not provide Reverse Polarity Protection or indication (ABYC E-

i. To comply with either the ABYC E- Ignition Protection Standard or ABYC E-11.4.30 requirements for installation in wet areas, a NEMA enclosure is available.

j. Insufficient current transformer inside diameter to accommodate twisted multiple #6 AWG marine conductors

k. Optional watertight boot available P/N 004-681 l. Optional watertight boot available P/N 004-683.

Further Information

Since 1979 Paneltronics, Inc. has been the industry-leading manufacturer of high-quality electrical power distribution panels. We now offer OEM’s our expertise in the design of Custom ELCI Panels utilizing readily available standard components that meet the new requirements presented in ABYC E-11.11.1. Call us today for an evaluation of your requirements.