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161

APPENDIX

TEST

MONTHLY

ELCI

30A

AC Shore Power Source

Main Circuit Breaker Branch Circuit Breaker

120V - 30A

3,000

3,000

120V - 50A

3,000

3,000

120/240V - 50A

5,000

3,000

240V - 50A

5,000

3,000

120 Volt–60 Hz

ELCI

Circuit

Breaker

3102

120/240 Volt–60 Hz

230 Volt–50 Hz

Hot

Neutral

Ground

120/240 Volt–60 Hz

Ground

Hot 1

Hot 2

Neutral

120 Volt–60 Hz

Hot

Neutral

Ground

AC Main Power Distribution

and Circuit Protection

Purpose

• Provide a path for delivering power from the ship’s sources of AC

power to the AC branch distribution system

• Provide a path for returning fault currents to ground via the green

safety Ground wire

• Provide a means for disconnecting AC power when the boat is not in

use or in emergencies

• Provide electrical separation to insure that two sources of AC power

are never connected

• Provide circuit protection for neutral and line wires in the AC

main system

• Provide ground fault protection

• Provide ELCI overload or leakage fault protection

AC Wire Systems

The three most common AC systems used on boats are shown here.

In all cases the ground, sometimes called safety ground to clarify its

purpose and differentiate it from the DC ground or negative, is said to

be a “normally non-current carrying wire.” Its purpose is to provide the

lowest resistance path for AC currents that have strayed from their

proper containment in the normally current carrying hot and neutral

wires. The ground wire is connected to the exterior conductive parts of

AC devices that could be touched by a person during normal operation,

and it conducts errant AC currents safely to ground rather than passing

them through a human body. The ground wire is never passed through

a circuit breaker.

Devices Qualifying as AC Main Circuit Breakers

In order to qualify as an AC main circuit breaker, these characteristics

must be present:

1.

The circuit breaker must have an Amperage Interrupt Capacity (AIC)

meeting the requirements of the following tables.

2.

The circuit breaker must be multiple pole, usually 2 or 3.

3.

The circuit breaker must be rated for the appropriate AC system

voltage in which it will be used.

4.

The circuit breaker must be available in amperages appropriate to

the design amperage of the system. In the USA, this is generally 30A

and 50A, while European systems are generally 16A and 32A.

5.

The ELCI shall have a leakage trip mechanism that trips if current

exceeding 30mA leaks to ground.

Sources of AC power, whether shore power or onboard generators

and inverters, should always have a circuit breaker near the power

source. This circuit breaker is designated the AC main circuit

breaker. The AC main circuit breaker should always have a pole for

each of the hot and neutral wires in the circuit assuring that circuit

protection functions are not compromised in reverse polarity

situations. Beginning in July 2010 ABYC Standards require that an

Equipment Leakage Circuit Interrupter (ELCI) with a 30mA leakage

trip be installed in shore power applications as the first protective

device after the power inlet. ELCIs respond to leakage of electrical

current outside of the intended current path, and provide overload

and short circuit protection. They serve as the main AC circuit

breaker for the system. These devices will open all energized

conductors and the neutral when opened manually or tripping on

an overload or leakage fault. For a more complete discussion of

ELCIs, see page 82.

ELCI

Circuit

Breaker

3102

TEST

MONTHLY

ELCI

30A

230 Volt–50 Hz

RCBO