Transcript QM-13d: Electricity Elective

QM-13d
Quartermaster
Electricity Elective
Instructors: George Crowl
Course Outline
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b. Electricity:
i) Know and demonstrate the correct method of rescuing a person in contact
with a live wire.
ii) Understand the construction of simple battery cells. Demonstrate the
proper care of storage batteries.
iii) Explain the difference between direct current and alternating current and
the best uses for each.
iv) Demonstrate that you know how to replace fuses, reset circuit breakers,
and properly splice shipboard electric cable.
v) Submit a diagram of the electrical system aboard the vessel used by your
ship.
vi) Explain wire tables, the current-carrying capacity of circuits, and the
hazards and prevention of electrical overloading.
vii) Explain electrolysis as applied to the deterioration of a boat’s underwater
fittings by galvanic action and its prevention.
QM-13d
i) Know and demonstrate the correct method
of rescuing a person in contact with a live
wire.
Rescuing a Person
 DO
NOT TOUCH THEM!
 You will get the same shock they have, and be
disabled
 Call 911. They will likely guide you.
 Cut off the power at circuit breaker
 If a line is down, DO NOT TOUCH
 Call power company, ask them to cut power
Still in Contact with Live Wire
 Stay 100
ft away from downed high wires! Do not
attempt rescue.
 Household current –
 Find wood or plastic pole (non-conducting)
 Dry rope is also non-conducting
 Pull wire free of person, or
person from wire
After Freed from Contact
 Move
away from danger
 Call 911 if not already done
 Lay person on back
 Check breathing and heartbeat
 Start rescue breathing or CPR
if needed
 Treat for shock, cover above and below
 Treat burns with cold water, no oil / grease
 Bad burns – cut away clothing, sterile dressing
QM-13d
ii) Understand the construction of simple
battery cells. Demonstrate the proper care of
storage batteries.
Battery Construction
 Lead-acid battery.
Ea cell = 2V, need 6 for 12V.
 Dilute sulpheric acid conducts electricity
 Positive = lead dioxide, negative = pure lead
 Positive = +, red; negative = -, black
Care of Storage Batteries
 Clean
terminals regularly (baking soda)
 Insure cells of conventional batteries are full with
distilled water
 Put a “boot” on the positive (red) terminal
 Light dielectric grease on terminals
 Insure tied down tight
 Eliminate wing nuts, they come loose
 Charge fully, 13V or more
QM-13d
iii) Explain the difference between direct
current and alternating current and the
best uses for each.
AC vs. DC
 Direct Current
(DC) flows in one direction at a level
voltage (below left), usually from a battery
 Alternating Current (AC) flows back and forth at
varying voltage (below right), usually from an
alternator or commerical power source
AC vs. DC (2)
 Shore
power is AC, powers lights, TV, microwave,
electrical sockets for tools, etc.
 Shore power is normally 110V, 60 cycle
 Commercial vessels may use self-generated AC at
240/480V to run motors, etc.
 Boat power is DC, powers nav lights, engine and
navigation instruments, cabin lights, etc.
 Boat power is 12V, does not cycle, generator
 Provided by 1-4 batteries, controlled by battery
switch. Special starting batteries sometimes.
AC vs. DC (3)
 AC
is needed to transmit electricity a long way over
power lines.
 High voltage can be transformed down to household 110V by transformers relatively easily
 Universally used for household and
manufacturing purposes
 DC is best for many electronic applications
 DC cannot travel far, so within a black box is OK
QM-13d
iv) Demonstrate that you know how to
replace fuses, reset circuit breakers, and
properly splice shipboard electric cable.
QM-13d
iv) Demonstrate that you know how to
replace fuses, reset circuit breakers, and
properly splice shipboard electric cable.
Replace Fuses
 Demonstrate, don't talk
 Fuses may
actually be hard to find, check your car
fuses if you don't have fuses on your boat
 Check fuse box list. If you don't have a list,
experiment (BUT start the list!)
 Turn off master switch if possible
 Remove fuse cover
Replace Fuses (2)
 Remove
(pull out or unscrew) fuse
 Inspect to see that it is blown (broken)
 Confirm proper fuse rating (in amps)
 Install fuse of equal or lower rating, then cover
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Common ratings – 10A, 15A, 30A
 If fuse blows quickly, solve the underlying problem
first! Then reinstall
another fuse.
 Overloaded circuits can
lead to fires
Reset Circuit Breakers
 Look like
small light switches
 Button forced out of alignment
 Run your hand along to find
one “popped”
 Push to “OFF”, then back “ON”
 If it pops again, fix the problem,
don't keep resetting C/B
Shipboard Cable Splicing
 Meet ABYC
standards (see NOTES for article)
 Use marine racheting crimp connectors
 Nylon-jacketed butt connectors (nylon tube)
 If exposed to water, use and melt heat-sensitive
adhesive to waterproof the connection
QM-13d
v) Submit a diagram of the electrical system
aboard the vessel used by your ship.
Electrical System
 Includes AC
and DC
 Shows batteries, motor, instruments, etc
 Uses conventional electrical diagram symbols
 Good starting source should be the motor electrical
diagram for your engine
 Most Sea Scout boats have been modified – show
reality, not the way it was built
 Probably will require you to use a circuit tester to
find out what reality is
N
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QM-13d
vi) Explain wire tables, the current-carrying
capacity of circuits, and the hazards and
prevention of electrical overloading.
Wire Tables
 Two
kinds – AWG and Metric (mostly AWG)
 Standardizes wire selection
 Provides conservative general guidance to the
public about how much current a wire can carry
 Design engineers will do a more precise job
 Sizes #0000 (0.46”) to #32 (0.008”), large to small
 For solid wire, stranded wire is based on total crosssectional area to carry same current
Typical Wire Table
 #16
wire
 Diameter – 0.0508”
 Diameter – 1.29032mm
 Ohms/1000' – 4.016
 Ohms/km – 13.17248
 Max amps for chassis wiring – 22
 Max amps for power xmsn – 3.7
 Max freq – 11,000 Hz
 Breaking strength – 75 pounds
Current-Carrying Capacity
 Also Current
Rating or Ampacity
 Depends on: insulation temperature rating,
conductor resistance, AC frequency, ambient
temperature, heat dissipation
 Insulation is often the driving factor
 Cables (several wires) have lower capacity because
of heat buildup, or conduit
 Figures are for continuous current, short overloads
will not usually affect
 Circuit breakers are sized to fit capacity
Electrical Overload Hazards
 Fire and
electrical arcing are main issues
 Overheated wire or arcing wire can start a fire
 Electrical arc could set off gasoline explosion
Overload Prevention
 Size your
circuit breakers and/or fuses to the current
capacity
 Loose or corroded wires increase resistance and
current. Means more current, possible arcing.
 Troubleshoot popped circuit breakers
 Unplug high current appliances (microwave, toaster,
waffle iron, etc.)
QM-13d
vii) Explain electrolysis as applied to the
deterioration of a boat’s underwater fittings
by galvanic action and its prevention.
Electrolysis, Galvanic Action
 Electrolysis –
“Chemical decomposition produced by
passing an electrict current through a liquid or
solution containing ions.”
 Galvanic corrosion – Two different metals will cause
corrosion if in contact, or if in water that can pass
ions from one metal to the other
Prevention
 Install one
or more zinc sacrificial anodes on the
prop shaft and/or other other equipment
 Check your berth for stray electrical currents
 Check your through-hulls at every quick haul
Questions?
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