The Connection Between Bonding, Grounding And
Lightning
Basic electricity for boat builders,
boat repairers and owners. How are all these systems connected?
The connection between AC, DC, Bonding,
Grounding, and Lightning
Protection systems.
I have talked to many boat owners and found that the electrical connection between
AC and DC is very misunderstood by most of them. Throw in Bonding,
Grounding and Lightning protection and people get so confused it becomes
a real muddle.
To separate the issues and understand what the connection is, where
it is, and why it is, you first need to start with some definitions.
You also need to think about these as separate systems that just
happen to be connected at one, and only one, point on the boat.
Also: ABYC and other authorities such as ISO,
make a distinction between the term Ground and the term Grounding.
In Europe and other parts of the world this may be called Earth
and Earthing. Ground in AC systems usually refers to the white neutral
wire and it's connection to the earth (or ground) and Grounding refers
to the third, green wire.
DC: Direct Current. A low voltage system
is usually 12 Volts, but on
large vessels can be 24, or 48 volts, to power basic equipment
using batteries. Anything over 50 volts, AC or DC, is considered
high voltage. DC is a two wire system, positive (red) and
negative (black or yellow), but there can be a third wire, a green
grounding wire or a grounding buss connected to the boat's ground. This
is not normally a current carrying conductor. See DC grounding
conductor below. See DC systems
https://newboatbuilders.co/pages/electricity1.html/pages/electricity1.html
AC: Alternating Current. Basically the same 60 cycle, 110 Volt system
(nominally 120 Volt) you have at home, with some very
important differences. It is a three wire system with a hot wire
(black), a neutral (white and also very hot) and a green wire. The
green wire (the safety wire) is an alternative path for current back
to earth and is not normally a current carrying conductor. See AC
grounding conductor below. 220 Volt AC systems are rarely seen
on boats in the USA but are common in Europe. These systems
will have a fourth red wire and are often seen in many homes in North
America powering electric clothes dryers See AC systems
https://newboatbuilders.com/pages/electricity7.html
Bonding: A separate system electrically connecting all metal fittings on the
boat that are in contact with the water, including the
sacrificial anode(s), and connecting them to the earth
ground, so they are all at the same voltage potential, zero.
There should never be any current in the bonding system. The
resistance of this circuit should be less than one (1) ohm.
See
https://newboatbuilders.com/pages/electricity6.html
Lightning Protection: A separate system to provide a direct,
low resistance path for lightning to earth ground while protecting
the boat and it's occupants. ( a very simplified definition)
See
https://newboatbuilders.com/pages/links_electrical.html for links
to lightning protection systems information.
Grounding System: See the ABYC definition of Ground below.
The following are taken directly from ABYC Standard E-11 AC and DC
electrical Systems on Boats.
11.4.1 AC grounded conductor
A current carrying conductor that is intentionally maintained at
ground potential.
NOTE: This may be referred to as the neutral (white) conductor
in AC electrical systems.
11.4.2 AC Grounding Conductor (green or green with a yellow stripe)
- a conductor, not normally carrying current, used to connect the
metallic noncurrent carrying parts of AC electrical equipment to the
AC grounding bus, engine negative terminal or its bus, and to the
source ground.
NOTES:
1. This may be referred to as the ground (green, or green with
yellow stripe) conductor in AC electrical systems.
2. The source of electrical power may be the shore AC power, an
inverter, an isolation transformer, or a generator.
11.4.9 DC Grounded Conductor - a current carrying conductor connected to the
side of the power source that is intentionally maintained at boat
ground potential.
11.4.10 DC Grounding Conductor - a normally noncurrent carrying
conductor used to connect metallic noncurrent carrying parts of
direct current devices to the engine negative terminal, or its bus.
11.4.11 Engine Negative Terminal - the
point on the engine at which the negative battery cable is
connected.
11.4.16 Ground
The potential of the earth's surface. The boat's ground is
established by a conducting connection (intentional or accidental)
with the earth, including any conductive part of the wetted surface
of a hull.
11.4.26 Polarized System (AC) - a system in
which the grounded and ungrounded conductors are connected in the
same relation to terminals or leads on devices in the circuit.
11.4.27 Polarized System (DC) - a system in which the grounded
(negative) and ungrounded (positive) conductors are connected in the
same relation to terminals or leads on devices in the circuit.
Grounding is making a connection between systems or equipment on a
boat to bring that system or equipment to zero voltage potential, or
earth ground. The grounding system may be connected to the engine
negative terminal, or connected to a grounding buss that is connected
to the engine negative terminal. This is not the same as the
Bonding system above. This is normally used for DC electrical
equipment. Some equipment on boats, that are not part of the
electrical system, need to be at zero potential and provide a path
to ground for any static electricity that may occur. In
particular the fuel system, fuel tank, fuel fill, and fuel tank
fittings need to be connected to ground to dissipate any static
electricity that may occur during fueling. The wires for the
fuel system ground go to the engine negative terminal or the
grounding buss.
Ground Fault: A ground fault is an AC hot wire, either black
or white, inadvertently touching something it isn't supposed to be
touching such as a metal case. It is not the same as two hot
wires shorting to each other. It is wires shorting to ground.
This can occur due to a breach in the insulation, a broken wire, or
a loose connection. Chafing on a sharp edge or rough surface can
abrade the wire and cause a break in the insulation.
Where are all of these systems normally connected?
The DC System is connected by the DC grounding conductor to the
engine negative or it's Buss. This is usually the wire from the
battery negative terminal to the engine cranking motor, but it can be
a separate wire from the battery negative to the engine block.
The AC system is connected to earth ground in two places, one on the
boat and one not on the boat. On the boat the AC grounding conductor (the green
wire) is connected to the earth ground at the engine negative
terminal. The other connection to earth ground is always at
the source of power, the power generating station, where the AC
Grounded conductor (the white wire, neutral) and the AC Grounding
conductor (the green wire) are connected to each other and
connected to earth ground by a rod driven into the earth.
Normally the green grounding wire and the white neutral wire are not
connected anywhere on the boat. The exception to this is, if you
have an isolation transformer, then there is no physical connection
from the boat to the earth ground at the power station, only
on the boat. The AC Grounded conductor (the white wire,
neutral) and the AC Grounding conductor (the green wire) are
connected to each other at the transformer, the source of power for
the boat.
If you have an on board generator, or an inverter then the AC
Grounding conductor is connected to earth ground internally inside
the generator or inverter, the source of power. But the only
connection on the boat that matters to you the
owner/installer/technician, is the connection to the engine
negative terminal or the grounding buss.
Additionally, the green Grounding conductor is connected to the
metal case of AC appliances, such as electric ranges, refrigerators,
washer/driers, microwaves, etc. This provides a path to ground if
there is an accidental short (a ground fault) in the equipment to the case.
If you touch the metal case the current goes through the wire
instead of through you. It is extremely important to check any
AC household appliances to see if the green wire is connected
internally to the white wire. This is commonly done on
household appliances. It needs to be disconnected. If you
leave this connected, then the green Grounding wire and the white
Neutral wire are connected on the boat and a shock hazard exists
because current is now flowing in the green wire. The green
Grounding wire should only be connected to the metal case.
Bonding wire: The bonding wire, also a green wire, is connected to
earth ground at the engine negative terminal or the grounding buss.
Lightning protection system: The lightning protection system is also
connected to the engine negative terminal. But when making
connections for the Lightning Protection system care must be taken
to follow the instructions in ABYC TE-4 Lightning Protection.
ABYC
www.abycinc.org.
ABYC has anticipated combining DC Grounding systems and Bonding
systems. In E-11 it says:
11.17.4 Combined Grounding and Bonding Systems
11.17.4.1 The DC grounding conductors may be combined with
the following systems providing all the requirements with respect to
conductor size are met for each system (see FIGURE 5 and FIGURE 11). You can purchase a current copy from ABYC at
https://www.abycinc.org
11.17.4.1.1 Lightning Protection - See ABYC
TE-4, Lightning Protection.
11.17.4.1.2 Cathodic Bonding - See ABYC
E-2 Cathodic Protection. (This is an old copy from 2013)
11.17.4.1.3 Static Electricity Grounding - See E-11.16.2.3, ABYC
H-24,Gasoline Fuel Systems, and ABYC
H-33, Diesel Fuel Systems.
The reason behind all of these systems being connected at the engine
negative terminal is the same for all of the systems. This puts the
system at zero voltage potential during normal operation, and
provides a zero voltage reference point from which to measure voltage
potential on the positive and hot side. The Grounding
wire acts as an alternative path for current back to earth ground, but only when
there is a ground fault in the system. This prevents shock hazards and
prevents you from being the path for current back to ground. It also prevents stray current
corrosion and galvanic corrosion. This is why it is very
important to insure that the green Grounding conductor is properly
connected and does not have any breaks in it, in order to conduct current
back to the source of power.
See the diagram below: Click on it to Enlarge.
Earth Ground: Some people do not agree with the premise that
connecting the grounding wire to the engine block provides a path
back to earth. However, water, whether fresh or salt, is an
electrolyte, and current will travel through it. Fresh water
is not as good a conductor as salt water and is a high resistance
path to ground. If you were measuring leakage current around a boat
in fresh water, and then did the same measurement in salt water the
current would be much higher in fresh. This is why AC leakage
is so dangerous to swimmers in fresh water. See Hot
Docks Electroshock Drowning
https://marinesurvey.ca/hot-docks/
There is still a danger in salt water although there is not as
large a current field around the boat. But the current will
definitely travel through the water back to earth. This has
been establish by research and experimentation.
However, this should never happen. There should never be
current from the grounding point into the water. If this
occurs then there is a ground fault in either the Black Hot wire or
White Neutral wire and a fault in the green Grounding wire. It
is broken somewhere. It is vitally important to maintain the
integrity of the green Grounding wire.
For DC systems some people prefer to not have a connection from the
battery negative to the engine block. This is what is commonly
called a floating, or isolated system. They believe this
prevents stray current from entering the water. Their belief
is simply that if you do not have an electrical connection to any
metal in touch with the water, then you can't have any stray
current. There is some merit to this argument. It will
prevent stray current corrosion, but it will not prevent galvanic
corrosion. See Corrosion On Boats
https://newboatbuilders.com/pages/corrosion.html
This is difficult to achieve in practice because the starter
(cranking motor) is grounded to the engine block on most engines,
and by connecting the negative wire to the battery negative, you are
connecting the engine block as well. This is the same as using
the engine block as a grounding point.
© newboatbuilders.com 2007 All rights reserved. revised
04/27/2021
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