Exercise 1. Answer the questions
Практическое занятие № 19-20.
Тема : Repair of electrical equipment. Types and characteristics of electrical wires
Цель: закрепить изученную лексику (профессиональные термины) по данной теме; совершенствование навыков ознакомительного чтения; употребления проф. терминов в устной и письменной речи.
Время проведения работы 1 ч 20 мин
Оборудование: словарь, компьютер, словарь тех. терминов.
Ход работы:
Изучите новые слова
Переведите текст на русский язык (устно).
Выполните упражнения после текста (письменно)
Vocabulary
bare wire голый провод
circuit breaker panel панель прерывателей цепи
conduit труба для электропроводки
cord шнур
flame-resistant огнестойкий
gauge калибр, сортамент
ground wire заземляющий провод
hardwired соединенный проводами
heat resistance теплостойкость
hot wire провод под напряжением
main feed магистральная линия (питания)
junction box распределительная коробка
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service drop ответвление к потребителю
sheathing оболочка
single strand wire одножильный провод
smoke detector датчик дыма
solid wire одножильный провод
stranded wire многожильный провод
wiring прокладка электрических проводов; электропроводка
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Text
The terms wire and cable are often
used to describe the same thing, but they are actually quite different. Wire is a single electrical conductor, whereas a cable is a group of wires swathed in sheathing.
Size of wires
Each application requires a certain wire size for installation, and the right size for a specific application is determined by the wire gauge. Com- mon wire sizes are 10, 12 and 14 – a higher number means a smaller wire size, and affects the amount of power it can carry. For example, a low- voltage lamp cord with 10 Amps will require 18-gauge wire, while service panels or subpanels with 100 Amps will require 2-gauge wire.
Wire lettering
The letters THHN, THWN, THW and XHHN represent the main in- sulation types of individual wires. These letters depict the following NEC (National Electric Code) requirements:
· T – Thermoplastic insulation
· H – Heat resistance
· HH – High heat resistance (up to 194°F)
· W – Suitable for wet locations
· N – Nylon coating, resistant to damage by oil or gas
· X – Synthetic polymer that is flame-resistant
Types of wires
There are mainly 5 types of wire:
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Triplex wires: Triplex wires are usually used in single-phase service drop conductors, between the power pole and weatherheads. They are composed of two insulated aluminum wires wrapped with a third bare wire which is used as a common neutral. The neutral is usually of a smaller
gauge and grounded at both the electric meter and the transformer.
· Main feeder wires: Main power feeder wires are the wires that connect the service weatherhead to the house. They’re made with stranded or solid THHN wire and the cable installed is 25% more than the load required.
· Panel feed wires: Panel feed cables are gener-
ally black insulated THHN wire. These are used to power the main junc- tion box and the circuit breaker panels. Just like main power feeder wires, the cables should be rated for 25% more than the actual load.
· 
Non-metallic sheathed wires: Non-metallic sheath wire, or Romex, is used in most homes and has 2-3 conductors, each with plastic insula- tion, and a bare ground wire. The in- dividual wires are covered with an- other layer of non-metallic sheathing. Since it’s relatively cheaper and avail- able in ratings for 15, 20 and 20 amps, this type is preferred for in-house wir- ing.
· Single strand wires: Single strand wire also uses THHN wire, though there are other variants. Each wire is separate and multiple wires can be drawn together through a pipe easily. Single strand wires are the most popular choice for layouts that use pipes to contain wires.
Color codes
Different color wires serve different purposes, like:
· Black: Hot wire, for switches or outlets.
· Red: Hot wire, for switch legs and for connecting wire between two hardwired smoke detectors.
· Blue and Yellow: Hot wires, pulled in conduit. Blue for 3-4 way switch application, and yellow for switch legs to control fan, lights etc.
· White: Always neutral.
· Green and Bare Copper: Only for grounding.
Exercise 1. Answer the questions
1. What is the difference between wire and cable?
2. What is the wire gauge?
3. What does wire lettering represent?
4. What wire type is used in service drop conductors?
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5. Why are non-metallic sheath wires preferred for in-house wiring?
6. What insulation is used in non-metallic sheath wires?
What color is the ground wire?
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