incandescent lightbulb or an electric water
heater.
Marine cranking amps (MCA):The number
of amps that a new, fully charged battery at 32°F
(0°C) can deliver for 30 seconds, and maintain a
voltage of 1.2 volts per cell or higher.
Megohmmeter:A specialized ohmmeter for
measuring extremely high resistance values,
sometimes referred to as an insulation resis-
tance tester. Readings are typically in the mil-
lions of ohms, far beyond the reading capabil-
ities of a digital volt-ohmmeter (DVOM). It is
often called a “megger.”
Milligauss (mG):^1 /1,000of 1 gauss, which is a
unit used for measuring the flux density of
magnetic fields. Milligauss are useful for mea-
suring magnetic field levels commonly found
in the environment.
Multiplexer:A communications device (black
box) that combines several signals for trans-
mission over a single medium.
National Electric Code (NEC):The preemi-
nent set of safety standards for electrical instal-
lations. Developed and published by the
National Fire Protection Association (NFPA).
National Marine Electronics Association
(NMEA):The foremost standards group in
North America that deals with marine elec-
tronics installations.
Network:A group of two or more computer
systems linked together to share information
and hardware.
Network architecture:The structure of a com-
munications network. An open architecture
allows adding, upgrading, and swapping of
components. It can be connected easily to
devices and programs made by other manufac-
turers. It uses off-the-shelf components and
conforms to approved standards. A closed archi-
tecturehas a proprietary design, making it diffi-
cult to connect the system to other systems.
The hardware manufacturer chooses the com-
ponents, and they are generally not upgradable.
Nonlinear load:In contrast to a linear load, a
load that will not have constant values in cur-
rent, voltage, or resistance. Examples are elec-
tronic control circuits for refrigeration systems
and motor loads.
Peak capture:A feature found on better elec-
trical measuring instruments that allows the
user to capture and record the maximum value
measured on a circuit with fluctuating values.
Power factor:The ratio of real power to
apparent power in an AC system. The amount
of current and voltage the customer actually
uses compared to what the utility supplies.
Protocol:In the context of data communica-
tion, a common set of rules, signals, and data
structures (for either hardware or software) that
governs how computers and other network
devices exchange information over a network.
Radiated power: The product of antenna
input power and antenna power gain, expressed
in kilowatts.
Radio frequency interference (RFI):Radio sig-
nals normally emitted from an electrical device
that negatively impact the quality of reception in
another electronic or electrical device. Symptoms
vary and can include loss of reception or, in a
television, reduced picture quality. RFI is a com-
mon problem on boats and a primary source of
equipment performance problems.
Reactive power:The difference between the
electrical power delivered to a system and the
power converted to useful work. Reactive power
is stored energy that is returned to the power
source.
Real power:The amount of electrical energy
that is converted into useful work. Also
known as active power or working power.
Residual current:In this context, leakage cur-
rent in an AC circuit. In an AC circuit, the hot
and neutral conductors cancel each other out
in a true-sine-wave power supply system.
When a current differential occurs between
the neutral and hot, this measured differenceglossary 207