Electrical Wiring Practices and Diagrams

Chapter 2Chapter 2

Electrical Wiring Practicesand Diagrams

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OverviewOverviewSafetyStandardsWiring ConsiderationsWire TerminationsCoaxial CableWiring InstallationsWiring Diagrams

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SafetySafetyLethal Current

Safety Precautions

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Lethal CurrentLethal CurrentFundamental policy of the USPS is

SAFETY

Human Body Resistance – 4 KΩ (moist skin) to 24 KΩ (dry skin) Safe current (through chest) – less than 20

milliamps

E = 120 VAC R = 4 KΩ I = ? I = 30 milliamps - NOT SAFE

Don’t want current through chest cavity (may be lethal)

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Safety PrecautionsSafety PrecautionsTurn circuit off

Disconnect service cordDisconnect negative battery cable

If must work on live AC circuitNeed 2nd safety person

Remove metal jewelryKnow your boat and its wiringUse outlet tester on AC outletsUse 3-wire extension cord from GFI

outletMElec-Ch2 - 5

StandardsStandardsAmerican Boat and Yacht Council

(ABYC)AC and DC Electrical Systems is E-11Minimum standards

Construction Repair

Marine Dept. of Underwriters LaboratoryTest and certify commercial productsSafety, not function

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Wiring ConsiderationsWiring ConsiderationsConductors

Wire Types

Wire Size

Wire Insulation

Wire Color Code MElec-Ch2 - 7

ConductorsConductorsConnects power sources to power

loadsCharacteristics

SafeDependableEfficient (minimal voltage drop)

Boat environmentWorse than either house or carHigh humidityVibrationCorrosive conditions

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Wire TypesWire Types

Marine GradeType 3 is recommended

Stranded copperTinned is preferred

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Wire SizeWire Size3% voltage drop

Critical circuits (Nav lights)Electronic Equipment

10% voltage dropCabin lightsMotorized Equipment

Minimum size AWG # 16MElec-Ch2 - 10

Wire Has ResistanceWire Has Resistance

Inadvertent ResistorsWire too small (min of #16 - properly size using table)Bad connections (or corroded connections)

Clean and tighten battery connectors Tighten lug screws and inspect wire to lug connection

Why do wires get warm / hot? Low resistance circuits pass high current (P = I2 x R) Wires can account for much of the overall resistance MEl

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V12 VDC0.1 Ώ

0.1 Ώ10A What Voltage?

An. 10 VDC

Wire Size ComparisonWire Size Comparison

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#16 top to #10 bottom

#2 top to #10 bottom

Copper Wire Copper Wire CharacteristicsCharacteristics

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12- VDC Wire Size 12- VDC Wire Size SelectionSelection

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12 VDC Wire Size 12 VDC Wire Size SelectionSelection

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120 VAC Wire Size 120 VAC Wire Size SelectionSelection

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What Size Wires?What Size Wires?

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B

Step 1Step 1

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What current to Load?

From Table 2-3 – Maximum of 44 feet (for 10A in #16 wire)

P = E * I I = P / E I = 1200/120

I = 10 Amps

From Table 2-1 – For 10A need #16 wire

B

Step 1 AnswersStep 1 Answers

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AMPACITY10 Amperes

#16 AWG TWby Table 2-1

for 3% voltage drop44 feet maximum

by Table 2-3

B

Step 2Step 2

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What current to Inverter?

From Table 2-3 – Maximum of 14 feet (for 110A in #1 wire)

Iload = Iout = Iin *0.91 Iin = Iout / 0.91 = 100 / 0.91 = 110 Amps

From Table 2-1 – For 110A need #1 wire

B

Iload = 100 Amps @ 12 V

Step 2 AnswersStep 2 Answers

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AMPACITY110 Amperes#1 AWG TWby Table 1

for 3% voltage drop14 feet maximum

by Table 2-2A

B

Wire InsulationWire InsulationAC cables must be type UL 1426 BC

600 volt insulationGasoline and Oil resistantWon’t absorb moisture

DC wires & cables must be Marine Grade600 volt insulationGasoline and Oil resistantWon’t absorb moisture

Color coded wires MElec-Ch2 - 22

Wire Color CodeWire Color CodeColor AC (Hot) AC (Neut) AC (Gnd) DC + DC -Black X X1

White XGreen (may have a yellow stripe) XRed X2 XYellow X1

Footnotes: 1 – Yellow preferred for DC negative to avoid confusion with AC Hot wire 2 – 2nd hot wire in 220 VAC is Red

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Wire Color CodingWire Color Coding

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Wire TerminationsWire TerminationsCrimping

Special ToolApproved Marine ConnectorsUse of Ratcheting Tool

Solder

Heat-shrink TubingMElec-Ch2 - 25

Wire TerminalsWire Terminals

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Ratcheting CrimperRatcheting Crimper

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YES

NO

Ratcheting Tool UseRatcheting Tool UseFirst select appropriate connectorStrip insulation length of stem plus

1/16”Insert stripped end all way into terminal

End should extend 1/16”Place terminal in same color slot

First crimp end of terminal barrel nearest ring

Then crimp wire end of terminal barrelCheck the connection with a solid tug

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SolderingSolderingTerminal connection can’t be only

solderedMust also be crimped

Soldering is normally not requiredCrimped connectors are acceptable to ABYCIf solder, apply only to ring end of terminal

Solder changes stranded wire into solidStranded wire is flexible

Use 40% lead / 60% tin, rosin core solderBattery lugs may be only soldered

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Heat-Shrink TubingHeat-Shrink Tubing

MElec-Ch2 - 30Application Steps

Coaxial CableCoaxial CableAntenna cableRadio coax is 50 ohm with PL-259Radio cable is cut to lengthWant attenuation under 3 dbTV cable is 75 ohm with “F”

connectorsGPS cable is not cut to length

Coil excess in 1-foot loops MElec-Ch2 - 31

Coaxial Cable InformationCoaxial Cable Information

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Soldering PL-259 Soldering PL-259 ConnectorConnector

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Wiring InstallationWiring InstallationBasic ConsiderationsDistribution PanelFuses / Circuit BreakersBranch Circuits

WireOutletsSwitches

Grounding SystemsBonding Systems MEl

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Basic ConsiderationsBasic ConsiderationsMust have source and return wires

Return wires to a common pointMay use feeder wire from power panel

for: engine, helm console, etc.

Wires above flood level of bilgeWaterproof if in bilge

Insulated support every 18”Twist DC wires within 1 meter of

compassMElec-Ch2 - 35

Distribution PanelDistribution PanelCentral location of Circuit Breakers / Fuses

All branch circuits from this location

AC and DC may be combined in one panelAll equipment / circuits should go to panel

Not direct to battery (except bilge pump) Noise interference suppression covered in Section 7

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DC / AC Power PanelDC / AC Power Panel

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Front View

Inside Power PanelInside Power Panel

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Buss Bars

Fuses and Circuit BreakersFuses and Circuit BreakersUsed to protect wiring from over

currentIn positive or hot wire

Newer boats use circuit breakersInitially more expensive

Replace blown fuse with correct ratingCircuit Breakers should be Marine

GradeTrip freeManual reset MEl

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Branch Circuits - WiresBranch Circuits - WiresMinimum size is 16 AWG

See Wire Selection TablesFor AC normally #14 for 15A and #12 for 20A

Must terminate in closed electrical box Of sufficient lengthDC negative returned to DC Panel

May use several negative feeder terminalsAC neutrals returned to AC PanelBonding system never used as return

wireMElec-Ch2 - 40

Branch Circuits - OutletsBranch Circuits - Outlets120 VAC outlets must be 3-wire polarized

Black (hot) to brass or copper colored terminal Outlet wires must have crimp terminalsGFI outlets

Required on weather deck, head, galley and machinery spaces

Good practice for all AC outlets to be GFITrip at 5 milliamps

Different outlets for AC and DC powerMElec-Ch2 - 41

Outlets and PlugsOutlets and Plugs

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DC Outlet(Receptacle)

DC Plug

120 VAC 120 VAC12 VDC 120 VAC

15 A Outlet

AC Plug 15 A

AC Plug 20 A

GFI 15 AOutlet

20 A Outlet

Branch Circuits - SwitchesBranch Circuits - SwitchesModern panels use Circuit Breakers

Which also double as switchesSwitches / Circuit Breakers

Must be Marine GradeRated for the voltage and current

controlledInterrupt the positive (DC) or hot (AC) leg

Battery SwitchDesigned for high current serviceNot located in engine or fuel-tank

compartmentsMElec-Ch2 - 43

Grounding SystemGrounding SystemGround is potential of water around boat

Or potential of earth’s surfaceDC – Ground Battery negative terminal(s)

Also engine blockWire color is Yellow (or Black)

AC – Transformer center tap on shoreAlso connected to ground rod at transformerWire color is Green and uninterrupted wire

Isolation transformers and galvanic isolators are exception and covered in Chapter 4 on AC

Engine, DC negative & AC ground connected

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Bonding SystemBonding SystemFor lightning protection

More in Chapter 6All metal objects should be bonded

Keeps all metal at zero potentialEngine blocksBattery negative terminals

Non-current carrying wireThrough-hull fittings

ABYC now recommends they be bondedElectrically isolated from metal hull MEl

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Bonding DiagramBonding Diagram

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Wiring DiagramsWiring DiagramsElements of a Good Wiring Diagram

Documents boat’s electrical layoutShould be kept currentUsed for troubleshooting

Component IdentificationPhysical objects to their symbolWires are color coded

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Wiring Diagram SymbolsWiring Diagram Symbols

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Switch, double pole, single throw (DPST)

Switch, single pole, single throw (SPST)

Switch, single pole, double throw (SPDT)

Battery (long line on top is positive)

Wires connected (at dots)

Wires crossing (but NOT connected)

Wire (insulated, metal conductor)Incandescent Light

Alternate symbol for Light

Circuit Breaker

Fuse

Ground

Male Connector

Female Connector

Simple DC Wiring DiagramSimple DC Wiring Diagram

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SummarySummaryCircuits should be off when working on themUse only marine grade properly sized wires

Tables will help determine proper wire size Minimum wire size is #16 AWG

Use wire terminations and ratcheting crimperDC circuits are 2 dedicated wires

Waterproof wire connection in bilgeAC circuits are 3 dedicated wires

GFCI in galley, head, machine spaces & weather deckSeparate Grounding & Bonding systems

requiredKeep wiring diagram current

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