MElecCh4 1

1
Chapter 4

• Alternating Current
• Power

2
Overview

• What is Alternating Current
• AC Hazards
• AC Power Requirements
• Shoreside Utility System
• On-Board Generators

3
What is Alternating Current

• General Description
• Basic Terminology

4
General Description

• Batteries provide limited amount of power
• Cant run air conditioner or heater
• DC appliances are expensive
• Therefore need for AC on boat
• From shore power
• From on-board generator
• Need Service Drop
• Not an extension cord
• Safety hazards with AC power

5
Basic Terminology

• Polarity Hot, neutral and ground
• Voltage 120 VAC
• Frequency 60 Hz
• Resistance DC opposition to current flow
• Reactance AC opposition to current flow
• Voltage Drop difference input output
• Wave Form Commercial AC is sine wave

6
Sine Wave

• Plot of AC Voltage is Sine Wave

7
AC Hazards

• Shock
• Fire
• Reversed Polarity

8
Shock and Fire

• Shock
• AC shock could be lethal
• Marine environment increases this hazard
• Need GFCI protection
• Fire
• Inadequate wiring and overloaded cables
• Over fusing or no overload protection
• Heater on extension cord

9
Reverse Polarity

• Reverse Polarity is extremely dangerous
• - Neutral is Hot (120 VAC not 0 VAC)
• - Produces stray current

Outlet checker indicates if AC outlet is
correctly wired
10
Reverse Polarity - 2

• Receptacles are polarized
• Plug can only be inserted one way
• Modern receptacles are polarized grounded
• Narrow vertical slot is Hot (120 VAC)
• Longer vertical slot is Neutral (0 VAC)
• Rounded hole is Ground
• ABYC requires a Polarity Indicator
• Normally lights on AC power panel
• If reverse polarity light is On
• DO NOT USE SHORE POWER
• Immediately disconnect the shore power cable

11
AC Power Requirements

• Maximum Current Limitations
• Priority Usage Table

12
Maximum Current Limitations

• Dockside Outlet
• Service Cord
• Boats Service Entrance

13
Dockside Outlet

• 30A outlet protected by 30A circuit breaker
• 15 A outlet protected by 15A circuit breaker
• If 15A to 30A adapter plugged into 15A outlet and
  30A cable plugged into adapter
• Current available limited to 15 Amps
• A 30A to 20A adapter permits a 15A cord to be
  plugged into dockside outlet
• NOT SAFE!
• No GFCI protection
• Outlet is overprotected

14
Service Cord

• 30A, 120 VAC service cord wire is AWG 10
• 50A, 120 VAC service cord wire is AWG 6
• Service cords are 25 and 50
• Cords are rated for 50 length
• Limit for 10 wire carrying 30A is 60
• Ch 2 Wire Size Selection Table
• When two 30A service cords connected together,
  safe current is limited to 20 Amps
• Similar problem for two 50A cords

15
Boats Service Entrance

• Has a maximum current rating
• Size for the service cord
• Service switch is DPST
• Breaks hot and neutral wires
• Normally left On
• If power is lost and circuit breakers are On
• Check service entrance switch
• Using one 30A service cord, rather than two
• and configuring power panel for one cord
• Service switch will trip if exceed 30A total

16
Priority Usage Table

• Maximum current limited by smaller of
• Dockside outlet and circuit breaker
• Service cord
• Service inlet and service switch (circuit
  breaker)
• Following table gives typical AC power use
• Everything cannot be on at same time
• Prioritize demand based on limiting factor

17
Priority Scheme
18
Shoreside Utility System

• Utility Power Distribution
• Shoreside Outlets
• Dockside Service Drop
• Shore Power Service Cable
• Connector Standards and Adapters
• Service Entrance and Distribution

19
Utility Power Distribution

• Power lines are at 2,300 VAC or higher
• Output from last transformer is 120/240 V
• If loads are balanced, no current in neutral
• Hot wires are Black and Red
• 120 VAC from either wire to neutral
• 240 VAC between black and red wires
• Center tap of transformer is grounded
• No current flows in ground (green) wire

20
Shoreside Outlets
21
Dockside Service Drops

• Shoreside power 120/240 V 60 Hz
• Cords and plugs are called 125 or 125/250 V
• Boats under 30 usually one 30A service cord
• Boats between 30 40 may use two 30A cords
• Larger boats one or two 50A 125/250 V cords
• Neutral wire is grounded only at transformer
• Inadequate service (brownout)
• Line voltage under 100 VAC
• May damage motors (refrigerator, air-conditioner)

22
Shore Power Service Cable

• Flexible, durable and oil/moisture resistant
• Called Hard Service Cable
• Compliant with NEC article 555
• Outlets are female Plugs are male
• Outlets / plugs are polarized with twist lock
• Outlets are keyed to prevent mismatch

30 Amps _at_ 125 V
50 Amps _at_ 125/250 V
23
Connector Standards
24
Adapters
25
Service Entrance Distribution

• Service Entrance Connector
• Isolation Transformer
• Galvanic Isolator
• AC Distribution Panel
• Branch Circuit Conductors

26
Service Entrance Connector

• Normally one or two
• 30A 125 V or 50A 125 V or 50A 125/250 V
• Most houses have 200A 125/250 V
• Close weatherproof cover when not in use
• Clean contacts with Electronic Cleaner
• Sequence for Shore Power service cord
• Turn Off all circuit breakers
• Connect boat end first
• Then connect shore end
• Turn On shore circuit breaker
• Check Reverse Polarity for proper connection
• Turn On boat Main then Branch circuits

27
Isolation Transformer

• No direct electrical connection
• between boat and shore power
• Avoids reversed polarity hazard
• Stops stray current
• Big and weight

28
Galvanic Isolator

• Solid state - large capacitor and power diode
• In series with green ground wire
• Blocks DC and low AC voltage
• Stops Stray current

29
Boat AC Distribution Panel

• Review of Chapter Two
• Normally combined with DC power panel
• Main (Shore Power) circuit breaker
• Not Service Switch (near input connector)
• Breaks both hot and neutral
• Branch circuit breakers
• Breaks only hot wire
• All AC circuits are 3-wire

30
Branch Circuit Conductors

• Review of Chapter Two
• Wiring is stranded 3-wire UL 1426 BC cable
• Normally 14 AWG for 15A circuits
• Normally 12 AWG for 20A circuits
• All neutral ground wires returned to panel
• Support wires every 18
• Ring connectors on both ends of wires

31
On-Board Generators

• Inverters
• Propulsion-engine driven generator
• Auxiliary-engine driven generator
• Isolation from Shore Power Entrance

32
Inverters

• Convert DC to AC
• 12 VDC to 120 V 60 Hz
• Efficiency 90 to 95
• Sizes from 50 to 3,000 watts
• 1200 watts of 120 VAC draws 110A of 12 VDC
• Outputs are 120 V 60 Hz
• True Sine Wave are expensive
• Run all loads
• Modified Sine Wave are less expensive
• May damage sensitive electronic equipment

33
Modified Sine Wave

• Modified Sine Wave and Sine Wave Voltage
• Either waveform will deliver the same power to a
  resistive load

34
Inverters - 2

• Automatically disconnect output when shore power
  or generator power is connected
• May produce interference
• Mitigation is discussed in Chapter 7
• Combined Inverter/Charger (illustrated)
• Either charge batteries or generate AC
• Lighter and cheaper than separate systems

35
Propulsion-Engine Driven

• AC Generators driven by propulsion engine
• Can only be used while underway
• Will not produce full output at idle
• Not as efficient as auxiliary driven generator

36
Auxiliary-Engine Driven

• Directly coupled to small gas or diesel engine
• Fuel should be same as propulsion engine
• Solution if need over 2 Kw of 60 Hz power
• Big, heavy and noisy

37
Isolation from Shore Power

• Inverters automatically only provide power to AC
  bus when no other AC power is present
• On-board Generators must also be isolated
• Normally done by transfer switch
• Neutral and ground are connected at generator

38
Summary

• Polarity reversed Dont use shore power
• Nominal shoreside power 120/240 volts, 60 Hz
• Maximum current limited (smaller of)
• Dockside circuit breaker, dockside outlet
• Service cord and boats service entrance
• Priority scheme for AC appliances needed
• Outlets must be 3-wire polarized
• GFCI in galley, head, machinery spaces weather
  deck
• Inverters for short term loads under 2 Kw
• Generators for long term loads over 2 Kw
• Use transfer switch with inverter or generator