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Absorption coefficient - Factor by which photons are absorbed as they travel a unit distance through a material.

Air Circuit Breakers - Are used to interrupt circuits while current flows through them. Compressed air is used to quench the arc when the connection is broken.

Alternating current (advantages) - Compared with DC, the advantage of AC is the reduced cost of transmission by use of high voltage transformers.

Alternating current (effects) - Effects of the AC to consider in determining the size of wires. Accordingly, allowance must be made for - Self-induction, mutual induction, power factor, skin effect, eddy currents, frequency, resistance, electric hysteresis, etc...

Alternating currents - Alternating current refers to a current that reverses at regular recurring intervals of time and that has alternately positive and negative values.

Alternating currents (disadvantages) - Compared with DC, the disadvantages of AC are - The high voltage which renders it dangerous and requires more efficient insulation; alternating current cannot be used for such purposes as electroplating, charging storage batteries, etc.

Ammeter - Measures the current flow in amperes in a circuit. An ammeter is connected in series in the circuit.

Amorphous semiconductor - Non-crystalline semiconductor material that has no long-range order.

Ampacity - Current-carrying capacity of conductors or equipment, expressed in amperes.

Ampere (AMP) - Practical unit of electric current flow. If a one ohm resistance is connected to a one volt source, one ampere will flow.

Ampere-hour (Ah) - Quantity of electricity or measure of charge. (1 Ah = 3600 C [Coulomb])

Anode - Positive pole of a battery, or preferably the path by which the current passes out and enters the electrolyte on its way to the other pole; opposed to the cathode.

Arc-fault Circuit Interrupter (AFCI) - Breaker that shuts off current in a circuit instantly when an arc fault is detected.

Armored Cable - Cable contains two insulated conductors and a thin aluminum or copper bonding strip inside a metal sheath. The metal sheath is the ground, not the bonding strip and be called Armor-clad, AC, or BX.

Array - Any number of photovoltaic modules connected together to provide a single electrical output. Arrays are often designed to produce significant amounts of electricity.

Ballast - The device that provides the current for fluorescent lights. Ballasts have become quite small, allowing the creation of compact fluorescent bulbs that can be used in place of incandescent bulbs.

Band gap - In a semiconductor, the energy difference between the highest valence band and the lowest conduction band.

Bare Conductor - Conductors not covered with insulating material.

Base load - Part of electricity demand which is continuous, does not vary over a 24-hour period and approximately equivalent to the minimum daily load.

Base power - Power generated by a utility unit that operates at a very high capacity factor.

Baseline performance value - Initial values of short-circuit current, open-circuit voltage, and current at maximum power measured by the accredited laboratory and corrected to Standard Test Conditions, used to validate the manufacturer's performance measurements provided with the qualification modules per IEEE 1262.

Bayonet Coupling - quick coupling device for plug and receptacle connectors, accomplished by rotation of a cam operating device designed to bring the connector halves together.

Beryllium Copper (BeCu) - Relatively expensive contact material with properties superior to brass and phosphor bronze. It is recommended for contact applications requiring repeated extraction and reinsertion because of its resistance to fatigue at high operating temperatures.

Bonding Jumper - Bare or insulated conductor used to ensure the required electrical conductivity between metal parts required to be electrically connected. Frequently used from a bonding bushing to the service equipment enclosure to provide a path around concentric knockouts in an enclosure wall - also used to bond one raceway to another.

Box - Device for mounting electrical fixtures and their wiring in walls and ceilings. Common varieties include new work, old cork, single gang, two-gang, fan, and junction.

Branch Circuit - Circuit conductors between the final over current device protecting the circuit and the outlet(s).

Breakdown Voltage - Voltage at which an insulator or dielectric ruptures, or at which ionization and conduction take place in a gas or vapor.

Breaker Panel - Is the electrical service panel which contains your house breakers. Most homes have an electrical panel outside which holds the main breakers and all of the 220 volt breakers. There will also be another panel inside the house which will contain all the 110 volt breakers

Bus - Heavy-duty, rigid connector that connects the circuit breakers or fuses to the incoming power and at times called a Busbar

Bus Support Insulators - Porcelain or fiberglass insulators that serve to isolate the bus bar switches and other support structures and to prevent leakage current from flowing through the structure. These insulators are similar in function of other insulators used in substations and transmission poles and towers.