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Basic Electricity - Page 10 - AC Circuits
Basic electricity for boat builders,
boat repairers and owners. What you need to know about the electrical
systems on your boat. Ground Faults, Generators, Inverters, Chargers.
Ground Fault Protection (shocks).
Ground fault protection, that is, protection against
accidental leakage of current to ground, is extremely important. It
protects the wiring on the boat from overheating and causing fires, and
protects the people from shock. Most ground fault protection is
accomplished by use of fuses or circuit breakers. But for protecting
people on the boat there are better solutions.
For a video on Grounding see
Basic Electrical Practices
https://newboatbuilders.com/pages/electricity12.html
Ground Fault Circuit Interrupters (GFCI)
Protecting the people on a boat is probably more important
than anything else. One of the best ways to provide protection against
shock is the use of a GFCI. Most of us are familiar with these now
because they are very common in our homes and at work. What a GFCI does is
monitor the current in both the black or hot wire and the white neutral
wire. As long as the currents are the same everything is ok. But if a
ground fault, that is leakage of current to ground, occurs then the
current in one wire is greater than the wire with the leakage. The
GFCI sees this imbalance between these two wires and shuts the
circuit off. They are extremely fast, tripping in milliseconds. In the US,
GFCI's are required to trip at 5ma. That's 5/1000 of an amp.
ABYC has a standard for GFCIs on boats
(ABYC, AC and DC Electrical Systems on Boats E-11.11),
They are necessary in any wet areas, such as the head, the galley, or anywhere you have an outlet and water. They are so
effective that when they trip many people do not realize anything has
happened, unless the lights go out.
Residual Current Device (RCD)
In Europe where ISO is the standard, they do it differently. There they
protect the whole boat rather than just certain areas on the boat.
They use what is called a Residual Current Device, or RCD. This
device is in the shore power inlet on the boat. An RCD works the
same way as a GFCI but the current at which they trip is much higher than
for GFCI. An RCD will trip at 30 ma, and they are slower than a
CFCI but still trip within 100 milliseconds. If it were lower there
would be a lot of nuisance or false tripping. But they do protect all of
the wires and equipment on the boat although they are probably not
adequate to protect the people from shock. In the US, ABYC has
included a device called an ELCI that is similar to an RCD.
ELCI: Electrical Leakage Circuit Interrupter
Much like an RCD. This protects the whole boat. This is the latest
standard requirement from ABYC (Also in ABYC E-11.11) An ELCI is
designed to detect current leaking into the water surrounding the boat.
It does this by measuring the current in the black (hot) wire and the
return current in the white wire (neutral). If everything is ok
the difference between the two should be zero. If there is an imbalance,
that is less coming back than is going, and this imbalance is 30 ma or
more for 100 milliseconds then the ELCI trips and shuts off all power.
This is to protect people in the water or if they touch metal that is in contact with the water. Every
year in the USA there are a small number of deaths from
electric shock drowning
https://www.electricshockdrowning.org/?page_id=23. The
ELCI is designed to prevent that. You can then isolate the problem by turning off
all of the equipment on the boat, turning the ELCI back on, and turning
on one device at a time until the ELCI trips again. The last item turned
on has the problem. Usually this is due to the green wire having been
cut or disconnected so that there is no return path for a ground fault.
Onboard Generators, and transfer switches.
So now you have power while at the dock. But what
about while you are underway, or anchored in a nice bay somewhere?
You need an alternative source of AC power. A generator can supply your
needs. It can also recharge your batteries so you can continue to run all
of your DC equipment. However, to properly use a generator's power you need
a power transfer switch.
A transfer switch shuts off the power from
shore and redirects the source of power to the generator. This is
absolutely necessary for safe operation of electrical equipment on board.
Most of these transfer switches are automatic, so once it's installed and
tested, you do not have to do anything else. No switches to turn on and
off.
If you choose to have an onboard generator it is absolutely imperative you
install a marine generator, not a portable generator designed for land
use. Marine generators are definitely more expensive, but they are
designed to withstand the marine environment, they are ignition protected,
and they are designed to mitigate Carbon Monoxide problems. Most are
diesel powered, but gasoline powered sets are also available. They
are designed to meet USCG regulations for permanently installed gas
engines. (33 CFR 183.401, 501,601) These include fuel system, electrical system, and ventilation
system regulations. In
recent years the manufacturers of the gasoline powered generators have
made serious reductions in the amount of CO these generators produce.
They have also made them much quieter. There is nothing more disturbing in
a quiet anchorage than when someone lights off a noisy generator.
Portable generators do not meet any of the above
requirements and should never be permanently installed in an enclosed
space on board. I am of the opinion that they have no place on board a
boat and should only be used on shore. This is a controversial
topic and some disagree with me. But I believe the carbon monoxide
and shock hazards present too great a risk.
Go
to Ike's List and find the links on Carbon Monoxide
https://newboatbuilders.com/pages/links.html .
Then read my Hot Topics on Portable
Generators
https://newboatbuilders.com/docs/portable.pdf
Inverters: https://en.wikipedia.org/wiki/Power_inverter
Inverters take DC power and change it into AC power.
With an inverter you can run some AC equipment, if it does not
require too much power. Air Conditioners and microwave ovens are two
appliances that are not normally run off of an inverter because of the large
amounts of power they need. There are systems with inverters powerful
enough to do this, but they should be designed by an electrician or
electrical engineer having experience with on board power systems. However, televisions, computers, VCRs and
other small appliances are easily run by an inverter.
You need to evaluate
what you want to use, and how much power you need, and convert that to how
large your house battery bank should be. These devices will rapidly
deplete a single battery. Select an inverter designed for marine use that
is ignition protected.
Converter/chargers
A converter is the opposite of an inverter.
It takes
AC power and converts it to 12V DC. Most of these have the dual function
of supplying DC to power your DC equipment, and charging your batteries.
The converter can be run off of the shore power, or off your onboard
generator. Select a converter designed for marine use, that is,
ignition protected.
Links to Offsite References:
Wiring Your Boat https://newboatbuilders.com/docs/WiringYourBoat.pdf
© newboatbuilders.com 2007 All rights
reserved. revised 02/25/2022
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