Business and commerce are totally dependent on electrical equipment and systems for energy, control and communications. These systems can be complex and the task to analyze failure consequences can be equally complex. Unrecognized consequences of failure, especially if the failure impacts personnel safety, can have unacceptable moral and legal implications as well as significant financial costs. Recent trends in workplace electrical safety shed new light on reliability needs for certain equipment in electric power and control systems.  One of them is the increasing attention given to mitigating arc flash hazards in electric power systems.

Historically, circuit protection devices served to protect the components in the electrical system from overcurrent or short circuit damage. Now there is an additional expectation from these devices. Selection of personal protective equipment to protect people from the thermal hazards of an arc flash event is based on the designed functionality of circuit protective devices. If these devices do not function as designed, the thermal and blast energy exposure may be orders of magnitude greater than expected . The arc flash hazard analysis and the selection of personal protective equipment are dependent on the protective devices to function as designated. In other words, the maintenance of certain devices and systems are critical to the safety of personnel who interact with the electric power equipment. Circuit breakers must function as new. Overcurrent devices must operate at the designed and documented pick up and time settings. If circuit breaks or protective devices are dependent on an external power supply, the tripping power system (usually batteries and battery charger) must function as designed. If the protective device is fuse, it must meet the design specifications and be the type, class and rating of the one documented in the arc flash analysis.

Equipment and systems that serve to mitigate arc flash hazards are examples of engineering control measures. These control measures establish the inherent safety by design performance of the electrical system. These measures, engineering controls, includes: hardware, equipment and systems whose designed intent is to prevent or limit exposure to a known hazard.

  The examples of engineering controls for electrical hazards are:

-Grounding and bonding systems

-Overcurrent protective devices

-Circuit breaker tripping power systems

-ground fault circuit interrupters

-High resistance grounding for power systems

-Enclosures to guard energized parts

-insulated power cords for tools and appliances.

Engineering controls function automatically to perform their functions. These engineering controls can be rendered inoperative due to improper installation, shortcomings in commissioning or functional testing, or maintenance deficiencies.

2. New word and word combinations to memorize:

failure  (of power) (n) – аварийное прекращение подачи электроэнергии

Arc flash – вспышка дуги

protection (n)- защита

overcurrent (n) –сверхток, ток перегрузки

damage (n) –повреждение

hazard (adj.) –опасный, опасность

exposure hazard- опасность возгорания

blast energy-энергия взрывной волны

exposure (n) –воздействие

maintenance (n) –техобслуживание, уход за оборудованием

setting (n)–установка, уставка

 trip (v)–расцеплять, размыкать

fuse (v) – плавиться

 mitigate (v) –ослаблять, подавлять

measure (n)-мера

inherent safety – внутренне присущая безопасность

controls (n)–органы управления

enclosure (n) – оболочка, кожух

power cord –двухжильный провод

 insulate (v) –изолировать

short-circuit (n)- короткое замыкание

shortcomings (n)-недостатки

commissioning (n)– ввод в эксплуатацию.

3. Answer the questions:

1/ Can the tasks to analyze failure consequences of electrical equipment be equally complex or easy? Why?

2 / What did the recent trends in workplace electrical safety shed new light on?

3  What is one of the recent trends?

4 / What did circuit protection devices protect the components in the electrical systems from?

5 / What is based on the designed functionality of circuit protection devices?

6 / What may happen if these devices do not function as designed?

7 / When must the protection device meet the design specifications?

8 / What are the examples of engineering control measures?

9 / What do these control measures establish?

10 / Why can these engineering controls be rendered inoperative?

4. Make word combinations with the noun “circuit”. Then match the combinations with the descriptions (1-5):

a____________________

a____________________

an____________________        circuit      

a____________________

a____________________

1. A circuit containing one or more sockets

2. A simple circuit where all the components are placed one after the other along the same conductor.

3. A microchip – a very small, often complex circuit.

4. What happens if live and neutral conductors touch while a current is flowing and there is no component or appliance between them?

5. A circuit which allows different components to be controlled independently by separate switches.

(Check up your answer:1-power, 2-series, 3- integrated, 4- short, 5- parallel)

(“Professional English in Use” by Mark Ibbotson. Cambridge University Press, 2009, p.97)