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Electrical Glossary (Q-Z)

Technical reference from www.Bluesea.com

Q, R

TRecreational Craft Directive - European Directive 94/25-EC relating to recreational craft.
Following are special definitions related to the RCD:

Committee Draft - the first draft circulated for comment by ISO Small Craft Technical Committee Working Group developing the standard.

The European Committee for Standardization.

Draft International Standard - an advanced draft where comments on the CD have been taken into account. Minor comments accepted by the Working Group will be incorporated in the FDIS, major changes will result in a second circulation as a DIS.

European Standard (Norme).

Final Draft International Standard - the last voting stage where standard bodies can only vote "yes" or "no" and the only changes will be editorial.

The International Council of Marine Industry Associations - the International Marine Industry Trade Association, which represents 24 national marine industry associations. That includes virtually all countries with an active marine industry in Europe, North America, Asia and Australia. Its officers and members represent its members' views at the EU Commission, ISO, and CEN and its members' representatives are actively involved in all the RSG Standards Working Groups.

International Standards Organization

The abbreviation used by CEN to identify a draft standard at any stage.

Working Group - the committee whose members have been nominated by their national standards body to develop any new standard required by the ISO Small Craft Tec. Committee (TC188) one of whom is chosen to act as the Convenor (Chairman/Secretary) by the TC188 members.
Austria ON Italy UNIBelgium IBN Luxembourg ITMDenmark DS Netherlands NNIFinland SFS Norway* NSFFrance AFNOR Portugal IPQGermany DIN Spain AENORGreece ELOT Sweden SISIceland* STRI Switzerland SNVIreland NSIA UK BSI
* EEA countries - whose national standards bodies are participants in CEN debates, but have a non-voting status.

recognized (UL recognized)
A device that is UL Recognized differs from a device that is UL Listed. A Recognized device is expected to be installed within a larger assembly by a manufacturer, not in the field, and this larger assembly is then expected to be tested by UL. The UL Recognition then allows UL to skip testing of the specific embedded Recognized component. UL Recognition has little value for end users installing devices in the field.

A device that allows current to flow in only one direction, such as a diode. Used to convert, or rectify AC current into DC.

regulator (voltage regulator)
A device, which uses a feedback loop to control the output of an alternator or other source. By measuring the output voltage and controlling the alternator field current, for example, the regulator is able to continuously adjust the alternator output to the desired voltage.

reserve capacity (battery)
RC is the number of minutes a new, fully charged battery at 80° F will sustain a discharge load of 25 amps to a cut-off voltage of 1.75 volts per cell (10.5V on 12V battery). This battery rating measures more of a continuous load on the battery.

The opposition to the flow of current in an electric circuit as defined by Ohm's law. The unit of resistance is the ohm, symbol , the Greek letter Omega.

reverse polarity
Describes a situation where the neutral and hot wires of an AC system are reversed. Most AC panels have an indicator to annunciate this condition, as it can be very dangerous.

RMS (Root-mean-square)
Root-mean-square (RMS) refers to the most common mathematical method of defining the effective voltage or current of an AC wave.
To determine RMS value, three mathematical operations are carried out on the function representing the AC waveform:

(1) The square of the waveform function (usually a sine wave) is determined.
(2) The function resulting from step (1) is averaged over time.
(3) The square root of the function resulting from step (2) is found.

In a circuit whose impedance consists of a pure resistance, the RMS value of an AC wave is often called the effective value or DC-equivalent value. For example, if an AC source of 100 volts RMS is connected across a resistor, and the resulting current causes 50 watts of heat to be dissipated by the resistor, then 50 watts of heat will also be dissipated if a 100-volt DC source is connected to the resistor.

For a sine wave, the RMS value is 0.707 times the peak value, or 0.354 times the peak-to-peak value. Household utility voltages are expressed in RMS terms. A so-called "117-volt" AC circuit has a voltage of about 165 volts peak (pk), or 330 volts peak-to-peak (pk-pk).


SAE (Society of Automotive Engineers)
An organization which sets standards for various equipment used in the automotive industry. Since much of the basic equipment used in the marine industry originates in the automotive industry it can be a relevant specifications body for the marine industry as well.

SAE wire gauge
Wire sizes as specified by the SAE, specifically for stranded wire, similar to the AWG, see also AWG. The same gauge in SAE wire has a smaller conductor than in AWG wire.

sacrificial anode
A less noble metal intentionally connected to form a galvanic cell with a more noble metal for the purpose of protecting the more noble metal from corrosion. Most commonly zinc.

safety green (ground) wire
The non-current carrying conductor in a three wire 120V or four wire 240V AC circuit, it provides a safe path for fault current. See also green ground wire.

sealed lead-acid see Gel Cell

A device whose ability to limit output power regardless of input power is intrinsic to its design.

The ABYC uses this term when discussing the allowable length of a conductor before it must have over current protection. The distance is extended if it is in a sheath.

shore power
AC utility power that is available when plugged into an outlet that is supplied from the main utility system.

short circuit
A conductive path of zero resistance. Typically refers to an unintentional connection between two conductors of opposite polarity. If a voltage is applied to a short circuit the current becomes very large and can start a fire, thus the need for short circuit, or overcurrent, protection in the form of fuses or circuit breakers.

A shunt resistor is a precise, low Ohm resistor that is temperature stable. It is used as a current "sensor" by using a millivolt meter to measure the voltage drop across it. Large current shunts are commonly made of one or more strips of manganin, a copper alloy capable of carrying high currents, that are soldered between machined blocks of brass with connecting bolts.

Shunts are rated according to the number of Amps it is capable of carrying and the mill votage which is generated across the shunt when the rated current is being passed through it. Common shunt ratings include 100A 100mV or 500A 50mv. The resistance can be calculated by using Ohms Law, V=IR, 50mV=500A(R), therefore R=0.1m, or 0.0001. This is a very small value of resistance; it must be in order to minimize the power loss when large currents are flowing.
The shunt normally has two separate screws on to which the sense leads are attached. It is important to realize that the integrity of these connections are critical to accurate measurement and should not be used as current carrying connections.

sine wave
A waveform that can be expressed as the graph of the equation y = sin x. The utility AC power is a sine wave.

single phase
The typical 120/240V AC system in the United States is a single phase system, meaning that the current flow in the two conductors is in phase or that they both cross zero at the same time.

skin effect
Skin effect refers to the phenomena of conductors' propagating AC current more efficiently on the conductors' surface than in its interior. This is because AC voltage changes polarity 120 times per second (60 Hz). Voltage signal penetration into the conductor interior takes a brief amount of time, so the current propagation in the interior lags that of the exterior, resulting in a longer period of propagation on the surface.

slow see Delay
The speed with which a circuit element such as a fuse or circuit breaker responds to an over-current condition.

slow blow see also delay
A fuse that is a slow blow has a longer delay when subjected to over-current, before it fails. Slow blow fuses are required for loads that have high starting surges, like motors.

solenoid (relay)
An electromechanical device that is used to switch large currents. It consists of a coil of wire and a moving contact that makes an electrical connection when the coil of wire is energized.

source isolation (AC)
The arrangement of multiple AC power sources in such a manner that two AC sources cannot be connected to the same circuit simultaneously.

source selector
A switch or breaker configuration, which allows the user to pick which source to have connected to the bus. Typically used in AC systems with multiple sources such as shore power and one or more generators.

speed see Delay
Indicates how fast circuit protection devices react, specifically with respect to over current protection and fuses.

square wave
An electrical waveform in which the current quickly goes from zero to its peak value in a step fashion. This is typical of inexpensive inverters.

starting bank
An arrangement of batteries that is designated for the function of engine starting.

storage battery
An electrochemical device capable of storing energy and releasing it and then able to be re-charged and repeat the process.

stray current
Unwanted current flows which occur due to a partial short circuit.

stray current corrosion
Corrosion that results when current from a battery or other external electrical (DC) source causes a metal in contact with an electrolyte to become anodic with respect to another metal in contact with the same electrolyte.

Sulfation is the formation or deposit of lead sulfate on the surface and in the pores of the active material of the batteries' lead plates. If the sulfation becomes excessive and forms large crystals on the plates, the battery will not operate efficiently and may not work at all. Common causes of battery sulfation are standing a long time in a discharged condition, operating at excessive temperatures, and prolonged under or over charging.

A large amount of current during the initial starting phase of a motor for example.

surge capacity
The measurement of the ability to withstand surge currents without damage.

surge current see also continuous current
The pulse of current that is associated with the initial large current required to start an electric motor, large resistive loads, and engine cranking.

An electro-mechanical device that is intended to open an electrical circuit and thus turn a load or source on or off.

switchboard see panel board


A connection point or device for an electrical circuit. A terminal strip is a series of screws which may or may not be in common to which wires are connected. Also refers to the connecting device which may be crimped on the end of a wire to enable it to be connected to the circuit with a screw, such as a ring terminal.

terminal studs
A threaded bolt onto which ring terminals may be placed and then fastened with a nut. Normally used for high current connections.

In a marine context thermal most commonly refers to a thermal circuit breaker, which uses the thermal effect of excess current flow to create differential expansion in a bi-metallic blade to open a circuit.
time-current curve see also Delay
A curve which depicts the relationship between the amount of current a fuse or breaker can withstand with respect to time.

tin plating
A plating of the element tin, which prevents corrosion. Commonly used to plate copper components such as a power bus.

toggle see also Pole
A switch which has a handle type actuator that can be placed in, at the most, three positions.

transfer switch, AC see Selector Switch, Source Isolation
An electrical relay or manual switch which selects an AC source alternative, such as a generator, shore power, or inverter.

transformer see Isolation Transformer

trip free
A circuit breaker designed to trip when subjected to a fault current, even if the reset lever is held in the ON position.

U, V

ungrounded conductor
Any conductor that is not connected to the Earth ground system

volt (voltage)
The unit of electric potential and electromotive force, equal to the difference of electric potential between two points on a conducting wire carrying a constant current of one ampere when the power dissipated between the points is one watt.

The product of volts and amps, which is watts in a DC system and the apparent power in an AC system.

voltage drop see line loss


The unit of power which for a DC circuit is equal to volts times amps.

Constructed or protected so that exposure to the weather will not interfere with successful operation in rain, spray, and splash.

wire amperage rating
The current a conductor can carry under a set of specified conditions such as open air, in an enclosure, and at a specified temperature.

wire sizing
The process of selecting the appropriate sized conductor for the amount of current to be carried while considering the length of the circuit.

withstand voltage
The maximum voltage level that can be applied between circuits or components without causing a breakdown.




Original article from Blue Sea Systems

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