ELECTRICAL TERMS COMMONLY USED Circuit ampacity: The ampacity of the com­ IN THE APPLICATION OF THE plete circuit, which would not be greater than CANADIAN , PART I the derated ampacity of the conductor or the rating of the conductor terminations. The following terms are used extensively in the application of the Canadian Electrical Code, Part I :* A device designed to open (1998). Together with the terms related to electric and close a circuit by manual means and to phenomena they constitute a "culture literacy" for open the circuit automatically on a predeter­ the electrical construction industry. Many of these mined overcurrent. Circuit breakers may not definitions are quotations or paraphrases of defin­ be used as snap unless especially itions given by the Canadian Electrical Code, rated for this use. Part I; these have been marked with an *. Circuit rating: The ampere rating of the over­ Ampacity:* The current in amperes a conductor current protective device installed to protect can carry continuously under the conditions of the circuit. use without exceeding its temperature rating. Conductor:* A wire, either copper or aluminum Bonding conductor:* A conductor that provides or copper-clad aluminum, used as part of an a low impedance path to ground. This path electrical system. Except when noted other­ augments the normal earth path. A grounding wise, wire is encased in an electrical insula­ conductor does not carry current except when tion as recognized by the Canadian Electrical a fault occurs between a current-carrying con­ Code, Part I. The exceptions are limited to ductor and ground. The primary purpose of grounding conductors and to grounded con­ grounding conductors is to prevent the electric ductors installed on the supply side of the ser­ shock of personnel and animals. An example vice. of a bonding connector is the grounding pin or blade on a cord attachment plug. Conductor ampacity: The ampacity of a con­ ductor identified by type and size as given in Branch-circuit:* The circuit conductors Canadian Electrical Code, Part I, Table 2. between the final overcurrent protection This definition is not valid for all situations. device protecting the circuit and the outlet(s). See derated ampacity and circuit ampacity. Branch-circuit selection current (BCSC):* Continuous load:* For loads up to 225 Refrigeration equipment may be marked with amperes, any load that in normal operation is this value, which shall be at least 64.1 percent on for more than one hour in any two hour of the hermetic motor compressor's maximum period is considered to be continuous. Larger continuous current. This value must be used loads are considered to be continuous if they when selecting the conductor sizes, the dis­ are on for more than three hours in any six connect , and short-circuit and overcur­ hour period. rent protective devices. Glossary 329

Current-limiting :* A fuse that will open potential as the grounding conductor, these are significantly before the current caused by a separate systems and should not be intercon­ fault reaches its maximum possible value (that nected except in the service equipment. is, in significantly less than 0.25 of a cycle). Intermediate metal conduit (IMC): Intermedi­ These fuses generally have silver links. ate metal conduit is a raceway commonly used Derated ampacity: The ampacity of a conduc­ in the United States. It has an outer diameter tor after the correction factors (Canadian slightly smaller than that of rigid metal con­ Electrical Code, Part I, Tables 5A and 5C) duit and a wall thickness approximately 60% have been applied. that of rigid conduit. IMC uses the same fit­ tings as rigid metal conduit and is threaded Dual-element fuse: A fuse with separate inter­ using standard pipe dies. rupting means for overload currents and for short-circuit currents; frequently called a time­ Interrupting rating:* A rating given to protec­ delay fuse or "Fusetron" (a trademark). tive devices to indicate the highest current that Fault: An inadvertent connection between any the device can interrupt without damage to associated equipment-lO 000 amperes is two conductors of an electrical system or any considered a low (poor) interrupting rating; conductor and ground. 100 000 amperes is acceptable except in rare Feeder:* Any set of circuit conductors providing cases. a connection between the service equipment and the branch-circuit overcurrent device(s). Maximum continuous current (MCC): A value that is determined by the manufacturer Fuse: A disposable thermal device providing of hermetic refrigerant motor compressors overcurrent protection. A fuse may be selected under high-load (high refrigerant pressure) to provide short-circuit, overload, and current­ conditions. This value is established in the limiting protection. Canadian Electrical Code, Part I, as being no Ground:* The earth or any conducting body greater than 156 percent of the marked rated that serves in place of the earth, essentially amperes or the branch-circuit selection cur­ establishing a universal point of equal poten­ rent. tial. The term ground is also used to designate Neutral conductor:* A grounded circuit con­ a conducting connection between an electrical ductor in a system that provides two or more circuit and the ground. line voltages of equal magnitude. Ground-fault circuit-interrupter:* A device One-time fuse: A fuse that is neither dual-ele­ designed to detect a difference of about 5 mil­ ment nor current-limiting. This fuse is in gen­ liamperes of current between the grounded eral the cheapest and offers less sophistication and the ungrounded conductors of a two-wire in circuit protection than other fuses. branch-circuit. This device is intended for pro­ tection of personnel. Outlet:* A point on a branch-circuit where cur­ rent is taken to supply utilization equipment. . Ground-fault protection:* A device installed to Overcurrent protection: A device that provides provide protection of equipment by the detec­ protection from current in excess of the rating tion of line-to-ground faults. Only required on wye-connected services with a rating of 1000 of the equipment or the ampacity of the con­ amperes or greater. These devices should be ductors. installed only by qualified personnel. Overload protection: An overcurrent protective device that incorporates a delay that allows Grounded circuit conductor:* A current-carry­ temporary overloads but will open the circuit ing conductor that has been intentionally con­ should current in excess of the device rating nected to ground. Although at the same persist for more than a brief period. 330 Glossary

Panelboard:* An assembly including a metal Short circuit: A connection between any two or cabinet and overcurrent protective devices more conductors of an electrical system in with connecting bus bars. Accessible only such a way as to significantly reduce the from the front, they are usually installed on or impedance of a circuit. When inadvertent, a in a wall. short circuit is referred to as a "fault." Rated load current (RLA): A value determined Short-circuit protection: An overcurrent pro­ by the manufacturer of the refrigeration equip­ tective device that responds instantly to short ment by actual operation (testing) at rated circuits, generally currents in excess of 600 pressure and temperature conditions and volt­ percent of the circuit rating. age. RLA is usually 64.1 percent of the com­ Switchboard:* A large, single-frame assembly pressor's maximum continuous current. When that contains overcurrent protective devices the same hermetic refrigerant motor-compres­ and usually instruments such as energy sor is designed into different manufacturers' meters. Generally accessible from the front models, the RLA rating of the products will and rear. Often used as service equipment in most likely be different. See maximum contin­ commercial buildings. uous current and branch-circuit selection cur­ rent. Ungrounded conductor: A conductor that has not been grounded, often referred to as a "hot" Selective coordination: The selection of over­ or line conductor. A potential difference may current protective devices with time-current exist between an ungrounded conductor and characteristics such that the effects of a fault the grounded conductor or between any two will be localized. This will minimize the inter­ ungrounded conductors of an electrical ruption of equipment operation. system. Service:* The conductors and equipment for Unit substation: Similar to a switchboard delivering energy from the supply (utility) except the unit substation will include high­ system to the wiring system of the premise voltage protective device(s) and being served. The service equipment always transformer(s). The installation of a unit sub­ includes one to six overcurrent devices that station requires that special attention be given can interrupt all electrical energy to the to noise control, ventilation, access for premises. replacement, and the possibility of flooding or other exposure to moisture.