Conductor Ampacity Calculation – Part One

In part one of this subject, I will list all the terms definitions that we can subjected to. 

These terms will include the following sections: 

  1. Conductor/Cable Terms, 
  2. Conductor/Cable Insulation Materials Terms, 
  3. Conductor/Cable Tests Terms, 
  4. Conductor/Cable Manufacturing Process Terms. 

Definitions for All above terms are included in the below table, please review it very well before we proceed to explain the steps of conductor Ampacity Calculations.

1- Conductor/Cable Terms
Ambient Temperature
Any all-encompassing temperature within a given area.
The maximum current an insulated wire or cable can safely carry without exceeding either the insulation or jacket material limitations. (Same as Current Carrying Ampacity)
Appliance Wire and Cable
Appliance wiring material is a classification of Underwriters Laboratories, Inc., covering insulated wire and cable intended for internal wiring of appliances and equipment.
Area of Conductor
The size of a conductor cross-section, measured in circular mils, square inches, etc.
Abbreviation for American Wire Gauge. A standard system used in the United States for designing the size of an electrical conductor based on geometric progression between two conductor sizes. Based on a circular mil. System 1 mil. Equals .001 inch.
Bare Conductor
A conductor having no covering. A conductor with no coating or cladding on the copper.
Building Wire
Wire used for light and power, 600 volts or less, usually exposed to outdoor environment.
Bunch Stranding
A group of wire of the same diameter twisted together without a predetermined pattern.
Buried Cable
A cable installed directly into the earth without use of underground conduit. Also called “direct burial cable”.
Wire used to connect two terminals inside of an electrical unit.
Joining of two conductors end to end, with no overlap and with the axes in line.
A splice where in two wires from opposite ends butt against each other, or against a stop, in the center of a splice.
A group of individually insulated conductors in twisted or parallel configuration, with or without an overall coating.
Cable Assembly
A completed cable and its associated hardware ready to install.
Cable Filler
The material used in multiple conductor cables to occupy the spaces formed by the assembly of components, thus forming a core of the desired shape (normally cylindrical).
The twisting together of two or more insulated conductors to form a cable.
Circular Mil
The area of a circle one mil. (.001”) is diameter, 7,845 x 10-7 sq. inches. Used in expressing wire cross sectional area.
A material applied to the surface of a conductor to prevent environmental deterioration, facilitate soldering, or improve electrical performance.
Coaxial Cable
A cable consisting of two cylindrical conductors with a common axis, separated by a dielectric.

Color Code
A system for a circuit identification through use of solid colors and contrasting tracers.
Combination Unilay
A stranding configuration that uses two strand sizes to achieve a 3% reduction in the conductor diameter without compression.
Compact Stranded Conductor
A unidirectional or conventional conductor manufactured to a specified diameter, approximately 8 to 10% below the nominal diameter of a non-compact conductor of the same sectional area.
Compressed Stranding
A stranding configuration with concentric strands, in which either all layers or the outer layer only is passed through a die to reduce the conductor diameter by 3%.
An insulating or jacketing material made by mixing two or more ingredients.
Concentric Stranding
A central wire surrounded by one or more layers of helically wound strands in a fixed, round, geometric arrangement.
In a wire or cable, the measurement of the location of the center of the conductor with respect to the geometric center of the surrounding insulation.
The capability of a material to carry electrical current, usually expressed as a percentage of copper conductivity (copper being 100%).
An uninsulated wire suitable for carrying electrical current.
Control Cable
A multi-conductor cable made for operation in control or signal circuits.
A small, flexible insulated cable.
In cables, a component or assembly of components over which additional components (shields, sheath, etc.) are applied.
Cross-Sectional Area
The area of a conductor exposed by cutting the conductor perpendicular to its longitudinal plane, expressed in circular mils, square inches, or square millimeters.
Current-Carrying Capacity
The maximum current an insulated conductor or cable can continuously carry without exceeding its temperature rating. It is also called ampacity.
Derating Factor
A factor used to reduce the current carrying capacity of a wire when used in environments other than that for which the value was established.
Any insulating material between two conductors that permits electrostatic attraction and repulsion to take place across it.
Direct Burial Cable
A cable installed directly in the earth.
An underground or overhead tube for carrying electrical conductors.
The circuit conductor between the service equipment and the final branch circuit over current device.
Fixture Wire
A conductor used in lighting or similar equipment or used to connect a lighting fixture to branch circuit conductors. Common types include TF, TFN, and TFFN.
Flat Cable
A cable with two smooth or corrugated, but essentially flat surfaces.
Flat Conductor
A wire having a rectangular cross section, as opposed to round or square conductors.
Flat Conductor Cable
A cable with a plurality of flat conductors.
Flex Life
The measurement of the ability of conductor or cable to withstand repeated bending.
The quality of a cable or cable component that allows for bending under the influence of outside force, as opposed to limpness which is bending due to the cable’s own weight.
The ease with which a cable may be bent.
A term used to denote the physical size of a wire.
Hard Drawn Copper Wire
Copper wire that has not been annealed after drawing.
Hook-Up Wire
A single insulated conductor used for low current, low voltage (usually under 600 volts) applications within enclosed electronic equipment.
A material having high resistance to the flow of electric current. Often called a dielectric in radio frequency cable.
Insulation Level-100%
Cable for use on grounded systems or where the system is provided with relay protection such that ground faults will be cleared as rapidly as possible but in any case within one minute.
Insulation Level-133%
Cable for use on grounded systems or where the faulted section will be de-energized in a time not exceeding one hour.
Insulation Resistance (I.R)
The resistance offered by insulation to an impressed DC voltage, tending to produce a leakage current through the insulation.
Insulation Thickness
The wall thickness of the applied insulation.
An outer covering, usually nonmetallic, mainly used for protection against the environment.
1,000 circular mils.
Leakage Current
The undesirable flow of current through or over the surface of insulation.
Conductors or other equipment included in a list published by a nationally recognized testing laboratory.
MC Metal-Clad Cable
MEC type designation for power and control cables enclosed in a smooth metallic sheath, or interlocking tape armor.
One thousand circular mils.
A group of insulated wires to be cabled with other stranded groups into multiple membered cable.
The linear supporting member, usually a high strength steel wire, used as the supporting element of a suspended aerial cable. The messenger may be an integral part of the cable or exterior to it.
Metal-Clad Cable
Type MC; a multi-conductor cable, similar to type AC, in which the conductors are twisted together under aluminum or steel armor. With or without an overall PVC covering.
A unit used in measured diameter of a wire or thickness of insulation over a conductor. One one-thousandth of an inch (.001”).
More than one conductor within a single cable complex.
Rated Temperature
The maximum temperature at which an electric component can operate for extended periods without undue degradation or safety hazard.
Rated Voltage
The maximum voltage at which an electric component can operate for extended periods without loss of its basic properties.
Rope Strand
A conductor whose cross-section is substantially circular.
Semi-Conducting Tape
A tape of such resistance that when applied between two elements of a cable, the adjacent surfaces of the two elements will maintain substantially the same potential.
A layer of insulating material such as textile, paper, polyester, etc. Used to improve stripping qualities, flexibility, mechanical or electrical protection to the components.
The outer covering or jacket of a multi-conductor cable.
A metallic layer placed around a conductor or group of conductors to prevent electrostatic interference between the enclosed wires and external fields.
Skin Effect
The tendency of alternating current, as its frequency increases, to travel only on the surface of a conductor.
Solid Conductor
A single unit not divided into parts.
A single uninsulated wire.
Stranded Conductor
A conductor composed of individual groups of wires twisted together to form an entire unit.
Temperature Rating
The maximum temperature at which an insulating material may be used in continuous operation without loss of its basic properties.
Tensile Strength
The pull stress required to break a given specimen.
Test Lead
A flexible insulated lead wire used for making tests, connecting instruments to a circuit temporarily or for making temporary electrical connections.
Thermal Rating
The maximum and/or minimum temperature at which a material will perform its function without undue degradation.
Tinned Copper
Tin coating added to copper to aid in soldering and inhibit corrosion.
Tray Cable
A factory assembled multi-conductor or multi-pair control, signal or power cable specifically approved under the National Electrical Code for installation trays.
Thermoplastic underground feeder and branch circuit cable.
Underground Service Entrance cable, rubber-insulated, neoprene or XLP jacketed.
Voltage Drop
The amount of voltage loss from original input in a conductor of given size and length or over a connection such as a termination.
Voltage Levels
Power-limited 0-300 volts. Low voltage 600-2000 volts. Medium voltage 5000-69000 volts.
High Voltage
Generally, a wire or cable with an operating voltage of over 35,000 volts.
Voltage Rating
The highest voltage that may be continuously applied to a wire in conformance with standards or specifications.
A flammability rating established by Underwriters Laboratories for wires and cables that pass a specially designated vertical flame test, formerly designated FR-1. Multi-conductor flat or round portable power cables without grounding conductor.
Water Absorption
Water by percent weight absorbed by a material after a given immersion period.
A single conductor, typically with a covering of insulation.
Wire Gauge
A measure of the diameter or size of wires. The sizes are expressed by numbers.
Yield Strength
The minimum stress at which a material will start to physically deform without further increase in load.
2- Insulation Materials Terms
Jacketing compound based on chlorinated polyethylene.
Ethylene Propylene Rubber (EPR)
An ozone-resistant rubber consisting primarily of ethylene propylene copolymer (EPM) or ethylene diene terpolymer (EPDM).
Flame Retardant
A chemical added in insulation materials to make them less combustible, such as antimony oxide (to PVC) or alumna trihydrate.
Flame Resistance
The ability of a material to restrict the spread of combustion to a low rate of travel, so that the flame will not be conveyed.
Thermoplastic-insulated machine tool wire. 90°C to 105°C, 600V.
A group of polyimide polymers that are used for wire and cable jacket.
Non-Contaminating PVC
A polyvinyl chloride formulation that does not produce electrical contamination through plasticizer migration.
A chemical agent added to plastics to make them softer and more pliable.
Polyethylene terephtalate that is used extensively in the production of a high strength, moisture resistant film used as a cable core wrap.
A thermoplastic material having the chemical identity of polymerized ethylene.
A substance made of many repeating chemical units or molecules. The term polymer is often used in place or plastic, rubber or elastomer.
A thermoplastic polymer of propylene.
Polyvinyl Chloride (PVC)
A thermoplastic material composed of polymers of vinyl chloride, which may be rigid or elastomeric, depending on specific formulation.
Portable Power Elastomer. Same as Type W, except that it is a thermoplastic elastomer insulation and jacket, whereas Type W is all thermostat.
Primary Insulation
The first layer of non-conductive material applied over a conductor, whose prime function is to act as electrical insulation.
Polyvinyl chloride, a common thermoplastic insulation and jacketing material for building wire and cable.
Type RH, a rubber or XLP-insulated conductor for use at 75°C in dry locations.
Type RHH, a rubber or XLP- insulated conductor for use at 90°C in dry locations.
Type RHW, a rubber or XLP-insulated conductor for use at 75°C in dry and wet locations.
Type RHW-2, a rubber or XLP-insulated conductor for use at 90°C in dry and wet locations.
Secondary Insulation
A high-resistance dielectric material whose flame is placed over primary insulation to protect it from abrasion.
The characteristic of a material whose flame is extinguished after the igniting flame is removed.
Indicates single conductor having synthetic thermosetting insulation of heat resistant, moisture resistant, flame retarding grade. Also made with chemically cross-linked polyethylene insulation. Used for switchboard wiring only, 90°C.
Junior hard service, rubber insulated pendant or portable cord. Same construction as type S, but 300B. Jacket thickness different.
Same as SJ, but neoprene, oil resistant compound outer jacket, 300V, 60°C
Same as type SJO, except oil resistant insulation and oil and weather resistant jacket.
Junior hard service, thermoplastic or rubber insulated conductors with overall thermoplastic jacket. 300V, 60C to 105C.
Same as SJT, but oil resistant thermoplastic outer jacket. 60C
Hard service cord, same construction as type S, except oil resistant neoprene jacket, 600V, 60°C to 90C
Service cord with oil resistant jacket, oil resistant and insulation and weather resistant. Also is water resistant. 600V.
Hard service, jacketed, same as type S, except all plastic construction. 600V, 60°C to 105°C.
A metallic compound added to PVC to maintain the integrity of the insulation compound during processing and use.
Same as ST, but with oil resistant, thermoplastic outer jacket. 600V, 60°C.
Service cord with oil resistant, thermoplastic jacket and weather resistant. STOW meets CSA approval for outdoor use. Can be water resistant. UL 600V.
Service cord with thermoplastic and weather resistant jacket, but not oil resistant. Can be UL water resistant. STW meets CSA approval for outdoor use. 600V.
Sunlight Resistance
The ability of a conductor or cable insulation to resist degradation caused by exposure to ultraviolet rays.
Canadian Standards Association type appliance wires. Solid or stranded single conductor, plastic insulated. 600V, 105C.
Fixture wire; thermoplastic covered, stranded with a nylon sheath. 90C.
90C, 600V, nylon-jacketed building wire for dry and damp locations.
Incorrect reference, commonly misapplied when THWN-2 is called out.
Thermoplastic, vinyl insulated building wire. Flame retardant, moisture and heat resistant. 75°C. Dry and wet locations.
75°C, 600V, nylon jacketed building wire for dry or wet locations.
90°C, 600V, nylon-jacketed building wire for dry or wet locations.
High temperature (90°C), chemically cross-linked, polyethylene jacketed, small diameter building wire.
Cross-linked polyethylene.
3- Conductor/Cable Tests Terms
Continuity Check
A test to determine whether electrical current flows continuously throughout the length of a single wire or individual wires in a cable.
Dielectric Test
A test in which a voltage higher than the rated voltage is applied for a specified time to determine the adequacy of the insulation under normal conditions.
Flammability Test
A test to determine the ability of a cable to resist ignition when placed near a source of heat or flame and to self extinguish when removed from this source.

Heat Shock
A test to determine stability of a material by sudden exposure to a high temperature for a short period of time.
Hi Pot
A test designed to determine the highest voltage that can be applied to a conductor without electrically breaking down the insulation.
Life Cycle
A test to determine the length of time before failure in a controlled, usually, accelerated environment.
A testing device that applied a DC voltage to a conductor and measures the resistance (in millions of ohms) offered by the conductors insulation.

Spark Test
A test designed to locate imperfections (usually pin-holes) in the insulation of a wire or cable by application of a voltage for a very short period of time while the wire is being drawn through the electrode field.
Tank Test
A voltage dielectric test in which the test sample is submerged in water and voltage is applied between the conductor and water as ground.
4- Manufacturing Process Terms
The process of controlled heating and cooling of a metal to achieve predetermined characteristics as to tensile strength and elongation. . Annealing copper renders it less brittle.
In wire manufacturing, pulling the metal through a die or series of dies to reduce diameter to a specified size.

The process of continuously forcing both a plastic or elastomer and a conductor core through a die, thereby applying a continuous coating of insulation or jacket to the core or conductor.
The process of uniting a compound with oxygen, usually resulting in an unwanted surface degradation of the material or compound.

In the next Article, I will explain the following points:

  1. Measurement Units of Conductors Cross Section Area, 
  2. Conversions between different Measurement Units of Conductors Cross Section Area, 
  3. Standard Sizes of Conductors, 
  4. Conductor Ampacity Tables. 

Please, keep following.

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