Author : Engr. Yousuf Ibrahim Khan (BSc. EEE, AIUB)
1. What is Electrical Safety ?
Ans : Electricity is a wonderful utility, but can be dangerous if not approached carefully. There are three basic hazards that cause injury or death – shock, arc-flash, and arc-blast. It is important to remember that even a small amount of current passing through the chest can cause death. Most deaths occurring for circuits of less than 600 volts happen when people are working on “hot,” energized equipment. So you need electrical safety.
2. What is a Shock ?
Ans : An electrical shock is a current that passes through the human body. Any electrical current flows through the path of least resistance towards ground; if an external voltage contacts a human body, e.g. by touching a live wire with the hand, the voltage will try to find a ground, and a current will develop that flows through the body’s nervous system or vascular system, and exit through the closest part of the body to ground (e.g., the other hand which may be touching a metal pipe.) Nerve shock disrupts the body’s normal electrical functions, and can stop the heart or the lungs, or both, causing severe injury or death.
3. Can you define Arc-Flash and Arc-Blast ?
Ans :
Arc-Flash : An arc-flash is an extremely high temperature conductive mixture of plasma and gases, which causes very serious burns when it comes into contact with the body, and can ignite flammable clothing. Arc temperatures reach up to 35,000°F – which is 4X the temperature of the sun’s surface!
Arc-Blast : Arc-blast is a pressure wave resulting from arcing, which can carry molten metal fragments and plasma gasses at very high speeds and distances. This can not only carry very hot shrapnel to injure a person, but can actually be strong enough to destroy structures or knock workers off ladders.
4. What is Electric Arcing ?
Ans : An electric arc takes place when current flows through the air or through insulation between two conductors at different potentials. Injury from arcs may be as a direct result of burning from the arc, in which case it is not unusual for the severity of the burn to be increased because molten metallic conductor particles may enter the burn. Arc burns are usually very severe and are often fatal.
5. How to avoid being shocked ?
Ans : Preventing yourself from receiving an electric shock can be summed up in three words: isolate, insulate and ground.
Isolate: Isolate yourself from the source of electric shock. Secure the power to equipment before you attempt to work on it. Be sure to keep all electrical equipment covers, doors, and enclosures in place when you are not actually working on the equipment. If you must leave circuitry exposed, rope off the area, post appropriate signs, and warn your fellow workers of the danger.
Insulate: Make sure that the electrical tools and equipment you use are properly insulated. Use only approved insulated hand and portable electric power tools. Check power and extension cords frequently for deterioration, cracks, or breaks. Breaks in the insulation cause many electrical accidents.
Ground: Electric current always follows the path of least resistance. To prevent yourself from being the unintentional path to ground, make sure that your equipment is well grounded. Well-grounded equipment will direct any stray electric current to ground, thereby protecting you from electric shock. A good ground can also help protect your equipment from excessive voltage spikes or lightning.
6. What is Earthing ?
Ans : The electric shock received by touching the metal parts of an appliance which might become live due to detective insulation is because of the current flowing through the human body caused by the voltage between the metal parts and earth. Effective earthing will keep zero potential in between such points and thus the accidents will be prevented.
7. What is Fusing ?
Ans : Fusing of electrical circuits is used to protect the wiring and equipment (NOT YOU). If you connect between active and neutral or active and ground you will get shocked. The fuse will happily deliver its rated current (1 - 50 A). More than enough to stop your heart or make you crispy. Fuses are also very important in preventing fires if a fault occurs.
8. Can you explain Mains Power ?
Ans : Single phase power is delivered on an active and neutral pair of conductors. The neutral conductor is tied to ground at certain locations. A separate ground wire is used to keep appliances at ground potential.
The neutral wire cannot do this as currents through it can cause a voltage drop, thus raising the voltage above ground.
9. What is an Earth Leakage ?
Ans : Current that flows to ground is called earth leakage and might be produced by water in an electrical appliance or someone standing on the ground touching something that is live.
10. What is a Power Surge ?
Ans : A power surge, also called a spike or transient, is a short-duration electrical disturbance with high levels of voltage and current. Depending on their source and magnitude, surges can cause immediate, catastrophic damage or the continuous degradation (latent damage) of electronic systems and components. Surges can come from sources inside and outside a building. Even under normal power conditions, surges are generated within a facility by the on/off cycling of electrical loads, such as air conditioners and compressors. These types of surges continuously assault electronic components causing them to malfunction or fail. Surges can be created when a disconnected electrical load is reconnected. For example, when the utility recovers from an outage and power is reintroduced to a building, a very fast high-voltage pulse is induced. This high-voltage pulse is due to the sudden change in current flow in the electrical distribution system. As a result, these changes in the system (disconnecting and reconnecting of loads) can create surges. Power surges assault circuit boards, control logic power boards and other components in electrical and electronic devices, causing them to malfunction or fail.
11. What is a Blackout ?
Ans : When an electric utility company is unable to provide enough power to meet its customer's demands, it will methodically turn off power to blocks of customers for a period of time. This power allocation helps ensure customers have electrical service, even if it is interrupted for a little while, rather than no power at all for extended periods of time. These power allocation events are known as "blackouts" or planned outages. Power Surges are caused from Blackouts.
12. What are Surge Protection Devices ?
Ans : SPDs or Surge Protection Devices are designed to "catch" a surge, then conduct the harmful levels of current away from the devices it is protecting. When building loads are re-energized and the utility reapplies power to the distribution system, spikes will be generated. SPDs sense the spikes as they enter the building electrical system and shunt them away before the surge can damage the building loads. In this way, loads are protected from the excessive voltage and current from a surge, so they are not damaged by them. So, the device that is used to safeguard against surges is called a surge protection device or SPD. SPDs reduce voltage surges to an acceptable level that can be tolerated by sensitive loads connected to the system.
13. Can you please tell me about Circuit Breakers ?
Ans : While a fuse protects a circuit, it is destroyed in the process of opening the circuit. Once the problem
that caused the increased current or heat is corrected, a new fuse must be placed in the circuit. A circuit
protection device that can be used more than once solves the problems of replacement fuses. Such a
device is safe, reliable, and tamper proof. It is also resettable, so it can be reused without replacing any
parts. This device is called a CIRCUIT BREAKER because it breaks (opens) the circuit.
14. What are Fuse Holders ?
Ans : For a fuse to be useful, it must be connected to the circuit it will protect. Some fuses are "wired in"
or soldered to the wiring of circuits, but most circuits make use of FUSE HOLDERS. A fuseholder is a
device that is wired into the circuit and allows easy replacement of the fuse.
15. What is a Surge Protector ?
Ans : A TRANSIENT VOLTAGE is a temporary, unwanted voltage in an electrical circuit. Transient Voltages are normally erratic, large voltages or spikes that have a short duration and a shout rise time. Devices like Computers, Electronic Circuits (TVs – Microwave Ovens – Sound Systems etc) require protection against Transient Voltages. Protection methods usually include proper wiring to National Electrical Code Requirements, to include grounding, shielding of the power lines, and use of Surge Protectors.
A Surge Protector is an electrical device that provides protection from high-level transient voltages by limiting the level of voltage allowed downstream from the Surge Protector/Suppressor (more commonly called a Surge Suppressor). Surge Protector/Suppressors can be installed at service entrance panels and individual loads.
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