Download The EM technician role over the last couple years has led each of

2010 ELECTRONIC MONITORING PROGRAM
FIELD SERVICES
ELECTRICAL SAFETY
14 JANUARY, 2010
The EM technician role over the last couple years has led each of us to work in an enviroment
whereby we are required to work with electricity, both alternating current (AC) and direct
current (DC) sources. As we are not formally trained electricians, this document has been
created to give a brief background on the differences between AC and DC current and things
we can do in our work environment to reduce the risk of electrical shock.
Firstly, it is VERY IMPORTANT to note that no EM technician is required to work on vessel
power related problems nor is the technician responsible for vessel power wiring. These
duties are the role of the skipper, crew member or person appointed by the owner or skipper
(for example a marine electrician).
On researching this information I came across two very good articles about AC and DC power
in marine environments which I have extracted the following information from.
The first article, titled ‘AC Electrical Safety’ was written by Terry Johnson, University of
Alaska Sea Grant, Marine Advisory Program for the journal Pacific Fishing, June 2001.
AC POWER
AC (120V) current must alternate between two points making a circuit. Coming from the
power source is the ‘hot’ wire, which normally has black insulation. Returning is the neutral
or ‘grounded’ conductor which is white. Neutral carries the same current as the hot wire. As
long as the current remains in this closed circuit there is no danger, but if it should escape (ie a
fault or short circuit) it will attempt to go directly to ground.
Some AC circuits have a green third wire, which is a ‘grounding’ wire. It parallels the white
wire and it connects to neutral at the power source. It is supposed to ground the circuit when a
short occurs.
The marine AC system is potentially more dangerous because the boat and the people who
work on it are surrounded by water. When a boat is floating, the water is the ground and any
metal that has an electrical path to it, including the hull of a metal boat or the engine of a glass
or wood boat via the shaft, becomes a path to the ground. Touching ANY of these items and a
HOT wire at the same time can send current through the body.
© ARCHIPELAGO MARINE RESEARCH LTD.
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ELECTRICAL SAFETY
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When the boat is afloat, inverters and gensets are grounded to the water via the engine shaft,
which act like the metal rod driven into the ground under your house. The risk aboard a boat
comes from a short that bypasses the grounding system and finds an alternate route to the sea.
Shore power presents a different set of potential problems. The shore power circuit is
grounded at the dock junction box through the shore power cord and receptacle. Faulty
installation, reversed polarity, defective or damaged cord or boat receptacle can create a
situation that could be hazardous.
Using an AC on the exterior of a floating boat is courting disaster. If a power drill or sander
gets splashed or falls overboard, seawater will conduct current from the hot wire to the case,
making the tool hot. If the grounding wire is not effective, any path to the sea via wet decks or
a metal conductor makes the worker part of the circuit.
Touching hot and neutral leads with one hand can give you a jolt and maybe even a burn, but
won’t kill you. Grabbing a hot lead with one hand and a neutral with the other, or the lead with
one hand while standing in water, can send the current through the chest. A person getting a
shock may be unable to release the item that’s carrying the current. The body becomes a
conduit between a hot AC wire and ground.
You don’t need to intentially grab a hot wire. Two-prong plugs inserted backwards into
sockets (a condition known as reverse polarity), circuitry chafes or cracks and exposed bare
wires can all lead to shocks.
To minimize the risk of shock:
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Use only copper multi-strand wire (preferably tinned boat cable) of correct size for the
load. We have provided a list of proper guage wire for specific lengths that the vessel
should adhere to.
Ensure that all connections are inside a panel box.
There should be no bare wires anywhere on the boat.
All AC outlets on baord must be three prong type. The V4 should plug directly into
three prong wall sockets, not extension cords and multiple socket plugs shouldn’t be
used onboard.
Never interconnect the AC and DC systems. These should be run through inverters or
the laptop power supplies we provide.
If you ever use shore power, connect at the boat end first, then the dock shore power
end. To disconnect, start at the shore power box and then the vessel.
Use only tools and appliances with three prong plugs, and if you must use extension
cords temporarily with power tools, use only cords with three prong sockets.
Shut off the generator, inverter and main AC panel before working on the AC system.
If you must work on the AC system live work with one hand behind your back to
avoid touching the hot and neutral or ground at once.
Remove jewelry, wrist bands or other conductive items.
Protective clothing, including rubber boots or rubber gloves offer some protection
from shock. Rubber ot plastic insulated handles on tools like pliers and screwdrivers
also help.
© ARCHIPELAGO MARINE RESEARCH LTD.
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ELECTRICAL SAFETY
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The second article was written by Robb Zuk from Pender Island, BC and has a website at
www.islandnet.com/robb/marine.html. Exerts from his Marine Electrical Check List are noted
below.
DC POWER
DC current is the unidirectional flow of electrical charge. The associated direct voltages are of
unchanging polarity. DC current is produced by such sources as batteries, generators, solar
power or thermocouples.
It is important to note that DC power will usually only shock a person. In these instances you
may be thrown from the source, unlike with AC power where it binds you to the source.
When referring to 12V (DC) wiring, ‘ground’, ‘negative’ and ‘ground return’ are all equivalent
terms. 12 V system is all ‘two wire’ type. All devices have insulated positive and negative
wires running to them.
PLEASE NOTE:
IN AN AC SYSTEM, HOT/BLACK, NEUTRAL/WHITE AND SAFETY GROUND/GREEN
OR BARE
IN A DC SYSTEM, POSITIVE(HOT)/RED OR COLOURED AND
NEGATIVE(GROUND)/BLACK. IF ONLY BLACK AND WHITE ARE USED, +/WHITE
AND -/BLACK.
In the marine environment, grounds from batteries, engine, bonding system, auxiliary power
generator, underwater ground plate, ships 120V safety-ground, all meet at one point. This
point must be a heavy bus bar or bracket with bolted connections. It should be labelled as a
common ground point.
Stray current is electricity that is flowing where it is not supposed to – through water, fittings
on your boat, wet wood, damp surfaces, etc. It can be a shock hazard and it can cause
corrosion (technically known as electrolytic corrosion).
An ‘at rest’ battery voltage is between 12.1 to 12.8 volts. A battery is at rest when it isn’t
being used and hasn’t received a charging current for at least 12 hours. A voltage above 12.8
volts indicates that the battery is still settling after a charge. A voltage below 12.1 volts
indicates either a weak cell or a battery charge below 50% capacity.
When running wire:
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All wire should be stranded (no solid wire).
It should be routed above water levels as practicable.
Conductors should not be kinked or bent sharply as this will fatigue the metal strands
and cause fracturing.
All wires have a flame retardant, moisture resistant protective sheath over their
insulation for the full length of the wire, except at the ends.
© ARCHIPELAGO MARINE RESEARCH LTD.
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ELECTRICAL SAFETY
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There should be no frayed or cracked insulation.
Wires are appropriate gauge for current being drawn and minimum size is 16 gauge.
If wiring is in conduit or troughs, drain holes exist to prevent collection of water.
Protected from mechanical damage in exposed areas.
Protected from chafing where passing through bulkheads, junction boxes, or other
holes.
Minimum of splices – unavoidable splices are soldered and sealed from moisture.
Wires approach terminals and devices from below, use drip loops. Water that may run
along wiring must not be able to wet connections or devices.
In making DC connections in a marine environment:
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Soldered joints are first mechanically connected (crimped, bolted or twisted).
Crimped or twisted connections are soldered as well. Connections held by solder
alone will fracture with little stress. Make sure solder is rosin core (60/40), not acid
core.
No connections are made with wire nuts, wire screws or marrettes. If you insulate a
soldered connection with a wire nut, turn it up so that water can’t collect in it.
Terminal connectors are ring type and correct size, they are not ‘forked’ or spade
connections. Ring type connections hold best if a wire is accidentally pulled or a
connection becomes loose.
Electrical tape does not hold up well in a marine environment. If tape is used for
moisture sealing or to insulate an awkwardly shaped connection, secure the finishing
end with a wire tie or cover as much of the tape as possible with shrink tubing or
vulcanizing tape.
An interesting item to bring up is Electrical Interference, or Noise. We have all seen stray
drum counts show up on the VDL screen, PSI voltage even though the hydraulics are off and
not to mention those dreaded BIOS issues which could be due to power fluctuations. This is
not saying that Noise is the culprit, but it is worth mentioning to make technicians aware.
To help prevent Noise:
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No electronic devise should be ‘on’ while the engine is being started or the winch is
operating unless they are in an isolated circuit. The voltage transients or ‘spikes’
generated by starter and winch motors can cause damage to sensitive electronics.
Watch for noise generated by gas engine systems, DC to AC inverters, electric fuel
pumps and radios. Electronics noise can be transmitted through wires or air.
Power wires for sensitive devices run separately from other wiring. Wires that run
parallel and close to each other can cause problems. Wires may cross without
affecting each other. Shielding may be required if close parallel wiring can’t be
avoided.
© ARCHIPELAGO MARINE RESEARCH LTD.
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