175 APPENDIX bluesea.com 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 3,000 230 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 vehicles 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 vehicle 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 Ground 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. 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. 120/240 Volt–60 Hz 120 Volt–60 Hz 230 Volt–50 Hz
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