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NEBOSH Diploma > Electrical Safety > Flashcards

Electrical Safety Flashcards

1
Q

Ohms Law

A

The value of a current passing through a conductor is directly proportional to the potential difference between the ends of the conductor, and inversely proportional to the resistance of the conductor

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2
Q

Resistance

A

The opposition to a steady electrical current

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3
Q

Impedence

A

Is the AC (alternating Current) equivalent of Resistance

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4
Q

Reactance

A

The opposition to the flow of alternating current

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5
Q

Inductance

A

The property of a conductor by which a change in current in the conductor induces a voltage in the conductor itself

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6
Q

Capacitance

A

The property of a circuit element that permits it to store charge.

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7
Q

Conductors

A

A conductor is any material that easily allows electrons to flow. Copper and Aluminum are two great examples of good conductors that are used extensively for electric cables

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8
Q

Insulators

A

Any material that inhibits the flow of electrons. Glass and rubber are good examples of insulating materials

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9
Q

Semiconductors

A

Used in the manufacturer of diodes, transistors and integrated circuit chips. They are neither conductors nor insulators. Examples include carbon, silicon and germanium

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10
Q

Alternating current (AC)

A

Mains electricity in the UK is AC. 230v supply in the UK. Current flows back and forth

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11
Q

Direct Current (DC)

A

Can be produced by batteries. Circuit flows in one direction only

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12
Q

Diode

A

Effectively an electrical one way valve, conducts the current in a forward direction but not in reverse. Used to convert (rectify) AC into DC

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13
Q

Electromagnetic Radiation

A

EMFA arise whenever electrical energy is used. Can lead to acute effects. At low frequency can affect the nervous system. At high can raise the body temperature

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14
Q

High Voltage

A

In excess of 650 V AC

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15
Q

Low Voltage

A

AC current exceeding 50 V but not exceeding 1000 V

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16
Q

Circuitry - Effects of components in a series

A

If 2 lamps are connected in series and one breaks the circuit is broken and the 2nd lamp can’t work.

When in series the same current flows through them and the voltage is shared between them

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17
Q

Circuitry - Effects of components in Parrallel

A

If lamps are connected in parrallel and one breaks the circuit is not affected and the second lamp will still work.
When in parrallel the current is shared between them but the voltage available remains the same

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18
Q

Earthing Prinicples

A

Earth is the conductive mass of earth, whose electrical; potential at any point is conventionally taken at zero

In order to reduce the risk of serious electric shock it is important to provide a path for earth fault currents to operate the circuit protection

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19
Q

Dangers from Electricity - B-Safe

A 
Burns 
Shock
Arcing
Fire
Explosion
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20
Q

Electric Burn

A

Due to heating effect caused by the passage of electric current through the body tissues
Painful and slow to heal, permanent scarring is common

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21
Q

Electric Shock

A

Response to electrical current flowing through the body. Electricity can take multiple paths through the body and is difficult to predict and can be very painful or fatal

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22
Q

Potentially fatal effects of electric shock

A 
Muscular contractions
Respiratory failure
Fibrillation of the heart
Cardiac Arrest
Injury from internal burns
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23
Q

Direct Shock

A

Direct contact is when a person comes into contact with a live conductor

24
Q

Indirect Shock

A

Indirect contact is when a person coming into contact with an exposed conductive part which is not normally live, but has accidently become live due to insulation failure

25
Arcing
Arcing generates UV radiation which causes damage similar to sunburn. Arcing faults occur if the energy available at a piece of electrical equipment is enough to maintain a conductive path through the air
26
Electrical Fires
Can occur in many ways: Overheating of cables or overloading of conductors Leakage of currents due to poor insulation Overheating of flammable materials too close to electrical equipment Ignition of flammable materials by arcing or sparking
27
Effects of AC on the body
More dangerous than DC. Causes muscular contractions which can lead to a person not being able to let go and can cause fibrillation of the heart muscle
28
Effects of DC on the body
Typically causes single convulsive contraction
29
Main hazards of static electricity
Creation of a spark that ignites an explosive or flammable atmosphere
30
Control strategies for Static Electricity
``` Equipotential Bonding and Earthing Humidification Antistatic additives Ionisation of the air Conductive flooring an footwear ```
31
Regulations covering Electricity
Electricity at Work Regulations 1989 (EAWR)
32
General duties of employer under EAWR
Electrical systems constructed so as to not give rise to danger Electrical systems are maintained so as to not give rise to danger All work carried out so as not to give rise to danger Protective equipment is suitable for use, in good condition and properly used.
33
Definition of Duty Holder under EAWR
Employer or self employed person so far as it relates to matters within his control. Employees also have duty to cooperate and comply with the regulations for matters which are within their control
34
Definition of Electrical system
An electrical system in which all electrical equipment is or may be electrically connected to a common source of energy, Includes equipment and source of energy
35
Definition of Electrical Equipment under EWAR
Anything used to generate, provide, transmit, transform, rectify, convert, conduct, distribute, control, store or measure electrical energy
36
'Strength and Capability' of electrical equipment
Ability of equipment to withstand the thermal, electromagnetic and electro-chemical effects of the electrical currents which pass through them
37
All conductors in a system should be....
Covered with insulating material and protected to prevent danger Placed or have other suitable precautions to prevent danger
38
3 main approaches to protecting against electric shock in the event of system fault
System designed and constructed so uninsulated conductors cannot become live - Double Insulation If they do become live the potential difference involved and the size and duration of current are such that no danger will arise - Earthing, Equipotential bonding, Use of safe voltages If they do become charges their environment is such that danger won't arise - Separated or isolated systems, Earth-free non-conducting environments
39
Ways to protect from excess current
Fuses and Circuit breakers
40
Isolation
The disconnection and separation of the electrical equipment from every source of electrical energy and disconnection and separation must be secure
41
Working space
Dimensions should allow people to move away from exposed live conductors without hazard and to pass one another with ease without hazard
42
Techniques used as protective systems
``` Earthing Fuses, mini-circuit breakers and residual current devices Double insulation Use of safe voltages Isolated systems Earth-free zones ```
43
Factors to determine the frequency of periodic inspection and testing of fixed installations
Commercial = Routine check annual, max period between formal inspections, 5 years or on change of occupancy Industrial = Routine check annual, max period between formal inspections 3 years
44
Reason for most electrical accidents
People believe equipment is dead but it is live It is known to be live but those involved do not have adequate training, equipment or have not taken adequate precautions
45
Working 'Live'
Should be exception to rule. Only permitted if: It is unreasonable in all the circumstances for the conductor to be dead It is reasonable in all the circumstances for the person to be at work on or near a conductor while live Suitable precautions (including PPE) have been taken to prevent injury
46
8 steps to planning, preparation and procedures for electrical work
1) Identify the electrical system and work to be done 2) Plan the work 3) Specify correct system of work 4) Select and instruct competent workers 5) Ensure correct working methods 6) Provide and ensure use of appropriate protective equipment 7) Provide information, tools and instruments and ensure workers are fully instructed 8) Arrangements for management checks and supervision
47
8 steps to dead working
1) Identify circuit or equipment to work on 2) Cut off supply, isolate and secure isolation 3) Retain keys. Post caution and danger notices 4) Prove circuit or equipment dead 5) Apply circuit main earth where necessary 6) Take precautions against adjacent live parts where necessary 7) Issue permit to work where necessary 8) Apply local earths
48
4 basic elements for working near buried underground cables/services
1) Planning the work 2) Plans 3) Cable-locating devices 4) Safe digging practices
49
Locating devices - 3 modes of operation
``` Power Mode (hum detection) Radio Mode (RF detection) Generator Mode (genny) (transmitter- receiver) ```
50
Max Voltage of overhead cables
400kV
51
Hierarchy of precautions for working near overhead power lines
Avoid working under or near lines Divert lines clear of the work area Make lines dead while the work is in progress Work around the live lines using appropriate precautions
52
3 categories of work around overhead power lines
1) No scheduled work or passage of plant under the lines 2) Plant will pass under the lines 3) Work will be carried out under the lines
53
Hot Glove Working
Involves staff working within safety distance zones and actually handling live conductors
54
Hot Stick Working
Involves use of Fibreglass Reinforced Plastic constructions as clamp and switch sticks
55
HSE Definition of Portable Appliances
Equipment that is not part of a fixed installation, but is intended to be connected to a fixed installation, or a generator, by means of a flexible cabler and either a plug and socket, or a spur box
56
Levels of checks for Portable appliances
1) Checks by the user 2) Formal visual inspections by a trained person appointed to carry them out 3) Combined inspection and tests by an electrically competent person

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