4. Lethal CurrentLethal Current
Fundamental 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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5. Safety PrecautionsSafety Precautions
Turn circuit off
◦ Disconnect service cord
◦ Disconnect negative battery cable
If must work on live AC circuit
◦ Need 2nd
safety person
Remove metal jewelry
Know your boat and its wiring
Use outlet tester on AC outlets
Use 3-wire extension cord from GFI outlet MEl
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6. StandardsStandards
American Boat and Yacht Council (ABYC)
◦ AC and DC Electrical Systems is E-11
◦ Minimum standards
Construction
Repair
Marine Dept. of Underwriters Laboratory
◦ Test and certify commercial products
◦ Safety, not function
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8. ConductorsConductors
Connects power sources to power loads
Characteristics
◦ Safe
◦ Dependable
◦ Efficient (minimal voltage drop)
Boat environment
◦ Worse than either house or car
◦ High humidity
◦ Vibration
◦ Corrosive conditions
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10. Wire SizeWire Size
3% voltage drop
◦ Critical circuits (Nav lights)
◦ Electronic Equipment
10% voltage drop
◦ Cabin lights
◦ Motorized Equipment
Minimum size AWG # 16
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11. Wire Has ResistanceWire Has Resistance
Inadvertent Resistors
◦ Wire 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
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V12 VDC
0.1 Ώ
0.1 Ώ
10A What Voltage?
An. 10 VDC
12. Wire Size ComparisonWire Size Comparison
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#16 top to #10 bottom
#2 top to #10 bottom
18. 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
19. Step 1 AnswersStep 1 Answers
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AMPACITY
10 Amperes
#16 AWG TW
by Table 2-1
for 3% voltage drop
44 feet maximum
by Table 2-3
B
20. 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
21. Step 2 AnswersStep 2 Answers
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AMPACITY
110 Amperes
#1 AWG TW
by Table 1
for 3% voltage drop
14 feet maximum
by Table 2-2A
B
22. Wire InsulationWire Insulation
AC cables must be type UL 1426 BC
◦ 600 volt insulation
◦ Gasoline and Oil resistant
◦ Won’t absorb moisture
DC wires & cables must be Marine Grade
◦ 600 volt insulation
◦ Gasoline and Oil resistant
◦ Won’t absorb moisture
Color coded wires MEl
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23. Wire Color CodeWire Color Code
Color AC (Hot) AC (Neut) AC (Gnd) DC + DC -
Black X X1
White X
Green (may have a yellow stripe) X
Red X2
X
Yellow 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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28. Ratcheting Tool UseRatcheting Tool Use
First select appropriate connector
Strip 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 barrel
Check the connection with a solid tug
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29. SolderingSoldering
Terminal connection can’t be only soldered
◦ Must also be crimped
Soldering is normally not required
◦ Crimped connectors are acceptable to ABYC
◦ If solder, apply only to ring end of terminal
Solder changes stranded wire into solid
◦ Stranded wire is flexible
Use 40% lead / 60% tin, rosin core solder
Battery lugs may be only soldered
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31. Coaxial CableCoaxial Cable
Antenna cable
Radio coax is 50 ohm with PL-259
Radio cable is cut to length
Want attenuation under 3 db
TV cable is 75 ohm with “F” connectors
GPS cable is not cut to length
◦ Coil excess in 1-foot loops
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35. Basic ConsiderationsBasic Considerations
Must have source and return wires
◦ Return wires to a common point
◦ May use feeder wire from power panel for:
engine, helm console, etc.
Wires above flood level of bilge
◦ Waterproof if in bilge
Insulated support every 18”
Twist DC wires within 1 meter of compass
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36. Distribution PanelDistribution Panel
Central location of Circuit Breakers / Fuses
◦ All branch circuits from this location
AC and DC may be combined in one panel
All equipment / circuits should go to panel
◦ Not direct to battery (except bilge pump)
Noise interference suppression covered in Section 7
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37. DC / AC Power PanelDC / AC Power Panel
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Front View
39. Fuses and Circuit BreakersFuses and Circuit Breakers
Used to protect wiring from over current
◦ In positive or hot wire
Newer boats use circuit breakers
◦ Initially more expensive
Replace blown fuse with correct rating
Circuit Breakers should be Marine Grade
◦ Trip free
◦ Manual reset
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40. Branch Circuits - WiresBranch Circuits - Wires
Minimum size is 16 AWG
◦ See Wire Selection Tables
◦ For AC normally #14 for 15A and #12 for 20A
Must terminate in closed electrical box
Of sufficient length
DC negative returned to DC Panel
◦ May use several negative feeder terminals
AC neutrals returned to AC Panel
Bonding system never used as return wire
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41. Branch Circuits - OutletsBranch Circuits - Outlets
120 VAC outlets must be 3-wire polarized
◦ Black (hot) to brass or copper colored terminal
Outlet wires must have crimp terminals
GFI outlets
◦ Required on weather deck, head, galley and
machinery spaces
◦ Good practice for all AC outlets to be GFI
◦ Trip at 5 milliamps
Different outlets for AC and DC power MEl
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42. 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 A
Outlet
20 A Outlet
43. Branch Circuits - SwitchesBranch Circuits - Switches
Modern panels use Circuit Breakers
◦ Which also double as switches
Switches / Circuit Breakers
◦ Must be Marine Grade
◦ Rated for the voltage and current controlled
◦ Interrupt the positive (DC) or hot (AC) leg
Battery Switch
◦ Designed for high current service
◦ Not located in engine or fuel-tank compartments MEl
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44. Grounding SystemGrounding System
Ground is potential of water around boat
◦ Or potential of earth’s surface
DC – Ground Battery negative terminal(s)
◦ Also engine block
◦ Wire color is Yellow (or Black)
AC – Transformer center tap on shore
◦ Also connected to ground rod at transformer
◦ Wire 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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45. Bonding SystemBonding System
For lightning protection
◦ More in Chapter 6
All metal objects should be bonded
◦ Keeps all metal at zero potential
◦ Engine blocks
◦ Battery negative terminals
Non-current carrying wire
Through-hull fittings
◦ ABYC now recommends they be bonded
◦ Electrically isolated from metal hull MEl
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47. Wiring DiagramsWiring Diagrams
Elements of a Good Wiring Diagram
◦ Documents boat’s electrical layout
◦ Should be kept current
◦ Used for troubleshooting
Component Identification
◦ Physical objects to their symbol
◦ Wires are color coded
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48. 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
49. Simple DC Wiring DiagramSimple DC Wiring Diagram
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50. SummarySummary
Circuits should be off when working on them
Use only marine grade properly sized wires
◦ Tables will help determine proper wire size
◦ Minimum wire size is #16 AWG
Use wire terminations and ratcheting crimper
DC circuits are 2 dedicated wires
◦ Waterproof wire connection in bilge
AC circuits are 3 dedicated wires
◦ GFCI in galley, head, machine spaces & weather deck
Separate Grounding & Bonding systems required
Keep wiring diagram current
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Notas do Editor
PowerPoint slides by
Stf/C Harl Porter, SN
Marine Electronics
[email_address]
Rear Commander for Electro-Mechanical Systems is
R/C Gene Danko, SN
Left is AC boat cable
Right is DC boat cable (yellow is new color for negative)
Major sections in this chapter
Major topics in Safety section
Good review of Ohm’s Law
Read Student Text section on Personal Safety Practices
(No notes)
Major topics in Wiring Considerations section
(no notes)
Type 3 stranded wire has more strands (than type 2)
i.e. #12 AWG
Type 2 has 19 strands
Type 3 has 65 strands
Manufacture tinned wire reduces oxidation and corrosion
(no notes)
Good review of Ohm’s law
Note that voltage drop in example exceeds 10%
Note the application of Ohm’s Law. P = I x E =I x (I x R) = I^2 x R. As resistance drops, the current goes up as the square – ½ resistance results in 4x current, which leads to heating.
Figure 2-1
Coin is a South Carolina quarter
Wire sizes on left (top to bottom)
16
14
12
10
Wire sizes on right (top to bottom)
2
4
6
8
10
Table 2-1
Table is a reference table – Gives max current per wire size
Equivalent to Table 2-3 (from West Marine catalog)
Note that distance is round trip distance
Given current (side scale) and round trip distance (bottom scale) gives wire size
Table 2-2
Same info as previous table
Given max DC current and wire length – gives wire size
Use of table will be explained in Figure 2-2
Table 2-3
Given max AC current and wire length – gives wire size
Use of table will be explained in Figure 2-2
Problem statement
Answers from Tables 2-1, 2-2 and 2-3
Start with determining current to load
Then given current of 10A
from Table 2-2A determine need #16 wire
Then given 10 A and #16 wire
from Table 2-3 determine maximum length of wires
Answers for wires from Inverter to Load
Power is power
AC current is 10 A
DC current if 100% efficiency is 100 A
I = P / E = 1200 / 12 = 100 A
But inverter is only 91% efficient
Therefore DC current is 100 / .91 = 110 A
Start with determining current to inverter
Then given current of 110A
from Table 2-1 determine need #1 wire
Then given 110 A and #1 wire
from Table 2-3 determine maximum length of wires
Note that at this load (110A), the battery must be de-rated and will not deliver 200AH. See Chapter 3.
(no notes)
(no notes)
Figure 2-4
Major topics in Wire Terminations section
Figure 2-5
Only marine grade nylon ring terminals or nylon flanged connectors (captive spade) are approved by ABYC for wire terminals. Marine grade nylon butt connectors are used to join wires together.
Nylon insulation is color coded to indicate wire size. Red is #22 to 16, blue is #16 to 14 and yellow is #12 to 10.
Ring hole or spade opening must match the screw or stud diameter.
Waterproof connectors are adhesive lined and after crimping are heated to shrink their insulation tight against the wire insulation.
Twist-on connectors (wire nuts) are prohibited on boats.
Figure 2-4
Specified by ABYC. Will not release until correct amount of crimp is applied.
Don’t use inexpensive stripper/crimper as is almost impossible to apply the correct amount of compression. Can be used to strip insulation from wires.
Makes good demonstration in class
Don’t use acid-core solder for electrical work!
Bottom is Figure 2-3B
Are waterproof terminal and butt connectors.
Heat-Shrink tubing can be used to make non-waterproof terminals and connectors waterproof.
Heat is best from a hair dryer on hottest setting.
Major section
Table 2-5
Figure 2-6
Steps in text under Installing Coax Connectors (PL-259 male connectors)
Installing TV coaxial “F” male connectors is also covered in text. Would be a good demo in class.
Major section
(no notes)
(no notes)
DC Side is on left
AC side is on middle and right
DC meters are switched to house, starting, or off
AC meters are switched to A service cord, B service cord or off
Note
All branches are protected by circuit breakers
DC side of power panel; AC side is covered by insulated cover (at right edge)
Note use of wire ties to minimize vibration at termination
Return wire buses are located directly behind the power panel
Trip free means cannot be held closed
Of sufficient length to:
Remove stress from connections
To permit fan-out and repair
Feeder terminals for engine compartment, helm console, fused panel
White (neutral) wire to silver terminal
Green (ground) wire to green terminal
AC Outlets normally installed as illustrated
Larger vertical slot (on left) in neutral
Smaller vertical slot (on right) in hot
Almost-round hole is ground
15A plug will mate with either 15 or 20 amp outlet.
20A plug will only mate with 20 amp outlet.
(no notes)
Ground system is very important safety feature
More in Chapter 4 on AC
More on Bonding in Chapter 6 on Lightning
Figure 2-7
Major section
Figure 2-8
Note symbols for crossing (not connected) and connected wires.
Are two options for crossing wires
Are three options for lights
Figure 2-9
Simple Series circuit
Point out Battery (top is positive), switch, fuse, light bulb, ground and cable connections
Given 12 VDC battery
What measure across open switch? An. 12 VDC
What measure across closed switch? An. 0 VDC
As drawn (switch open), what measure across light bulb? An. 0 VDC
With switch closed what measured across light bulb? An. 12 VDC
What measured from engine block to “top” of light? An. 12 VDC
(Engine block is grounded (connected to battery negative))
What color should wire be from “top” of battery to switch and fuse?
An. Either red (generic) positive or Dark Blue (cabin lights)
What color should wire be from “bottom” of battery to light?
An. Either yellow (new ABYC color for negative) or black (old ABYC color)