b part 14 electricity

Electricity at Work

Basic Principles of Electricity

Volt = Electrical pressure

Ampere = Electric current flow

Ohm = Electrical resistance (or impedance)

Power (watts) = voltage x current

Electrical Hazards

Electric shocks

Electric burns

Electrical fires

Electric arcing

Explosion

Portable Electrical equipment

Electrical Control Measures

Insulation/Enclosure of live parts

Low Voltages

Earthing

Fuse

Circuit Breaker

RCD

Equipotential bonding

Isolation

Insulation/Enclosure of Live Parts

Live parts cannot be touched

If equipment has a metal enclosure,

precautions must be taken to prevent

metalwork becoming live. This is achieved

by double insulation in which live parts are

covered by 2 layers of insulator.

Each layer is capable of adequate

insulation

Low Voltages

For hand tools, the 100 volt centre-tapped

(CTE) system is recommended.

System relies on the mid-point of the

reduced voltage transformer to be earthed

Maximum shock voltage is 55 volts, but full

110 volt supply powers the equipment

Earthing

By connecting exposed metal parts to

earth, any fault current is provided with low

impedance path to earth I.e. one with little

resistance so that fault current will operate

protective devices and cut off the supply by

breaking the circuit

If all exposed metalwork is properly

bonded to earth, it cannot be made live by a

fault and the risk of shock is eliminated.

Fuses

Forms a weak link in a circuit by

overheating and melting by design if the

current exceeds the safe limit

Rating should be above operating current

required by equipment but less than the

current rating of the cable in the circuit

Circuit Breakers

A mechanical switch which automatically

opens if the circuit is overloaded

Rating should be above operating current

required by equipment but less than the

current rating of the cable in the circuit

RCDs

Interrupt supply in event of a small leak of current to earth

Sensitivity can be adjusted so that shocks are not lethal

Determine when a current flows to earth by comparing current in live and neutral conductors

Test buttons should be regularly checked

Equipotential Bonding

All extraneous metalwork is is connected

by a common bonding conductor which

ensures that all the metalwork is at the

same potential

Current will not flow between two points at

the same potential

A common connection to earth is usually

made

Isolation

Isolation means depriving something of power, AND ensuring that tit cannot be re-energised

Establishes an effective barrier between equipment and supply and ensures that no unauthorised person is able to remove the barrier

Should be clearly labelled

Other Control Measures

Insulating gloves

Insulating mats

FR clothing

Insulated tools

Face shields

Shrouding

Distance

Portable Electrical Equipment

Control Measures

Regular checks/maintenance

Roll out leads

Do not use in harsh conditions

Manufacturers instructions

110v CTE system

Electricity at Work Regs 1989

Require that all electrical systems should be:

• Constructed & maintained to prevent danger

• Regularly checked & tested by a competent person

• Suitable & sufficient for the environment in which they are to be used

• Protected by earthing, double earthing, double insulation and/or RCDs

• Capable of being made dead (isolated)

Live working should only be used as a last resort and then with all due precautions to prevent/minimise injury

Systems should normally be made dead, checked and isolated so that they cannot accidentally become energised – may require PtW systems

Maintaining Electrical Equipment

User checks

Formal visual inspections

Combined Inspections and tests

Maintenance and test records

Frequency of maintenance

User Checks

Check for:

• Damage to cable sheath

• Damage to plug, casing or pins

• Inadequate joints or taped joints

• Coloured internal cables showing

• Wet or contamination

• Damage to external casing or loose parts or screws

Equipment should be taken out of use and reported immediately

Formal Visual Inspections

Carried out by competent person

Most faults can be picked up this way

Include removal of plug cover and checking fuse

Provide simple written guidance

Faulty equipment should be taken out of service and not used until properly repaired

Data should be kept and can be used to identify trends

Combined Inspection & Test

Likely to be justified when:

• Reason to suspect equipment may be faulty

• After repair or modification

• At periods appropriate to the equipment

PAT testing

Maintenance & Test Records

Useful for reviewing & monitoring

effectiveness of maintenance regime

Can be used as inventory of equipment and

a check on use of unauthorised equipment

Can be used to identify trends

Useful to label equipment

Frequency of Inspections

Factors to consider:

• Type of equipment e.g. portable or hand held

• Manufacturers recommendations

• Initial integrity and soundness

• Age of equipment

• Working environment e.g. wet , hot, dusty

• Frequency and duration of use

• Foreseeable abuse of equipment

• Effects of any modifications or repairs

• Analysis of records of previous maintenance

Effects of Electric Shock

Muscular contractions

Respiratory failure

Fibrillation of the heart

Cardiac arrest

Burns

Can result in secondary injuries e.g. falls

from height or muscle tears

First Aid for Electric Shock

Break contact between current and victim either by switching off or removing victim

Ensure rescuer does not come into contact with anything live e.g. victims skin

Artificial respiration should commence immediately and continue until the victim recovers or qualified medical aid intervenes