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Control measures when working with electrical systems (Safe systems of…
Control measures when working with electrical systems
Protection of conductors
All electrical cables should be insulated to prevent direct contact with conductor
Insulation should consist of unbroken, undamaged sheath
Insulation of conductors must be ensured where cable meets point of entry for plug
Strength & capability of equipment
Carefully selected to ensure it is suitable for the particular electrical system, the task it is expected to perform & the environment in which it will be used
No electrical equipment should be put to use where its electrical strength & capability may be exceeded
Used with manufacturer's rating & compliant with manufacturing standards (national & international)
Environments where risk could be increased;
Weather rain, snow, ice, extreme temperatures
Corrosive environments (acids)
Flammable substances
Contamination due to water ingress dust
Constant use
Physical damage to cables - moving traffic on construction site
Fuse
Principles
Device within an electrical circuit to prevent overload
Allows electricity to flow through it as part of the circuit
If overload occurs, the fuse melts therefore breaking the circuit
Advantages
Cheap & reliable
Easily replaced
Limitations
Protects the circuit but not the people
Easy to install the wrong rated fuse
Earthing
Principles
One end of the earth is connected to metal casing of equipment, the other end to earth
If a fault occurs, the flow of electricity will go to earth rather than through the individual
A way of protecting equipment & people when an electrical fault occurs
Advantage
Protects people from electric shock
Limitation
The earthing wire may be damaged or disconnected making protection inadequate
Isolation
Principles
Excellent way of achieving safety by making circuit dead
Simplest form is switching off or unplugging
Involves the removal of electrical power from the circuit
Lock out, tag out system to prevent accidental start up
Advantages
Effective way of preventing injury when working on an electrical circuit
Limitation
Certain testing or fault finding can only be done when the circuit is live
Double isulation
Principles
Consist of a layer of insulation around the conductor & a second layer around the first
Often the second layer is casing of equipment which cannot become live (non-conducting plastic)
Advantages
Does not rely on the electrical system directly for protection
Creates a physical barrier between conductor & person
Limitation
Must be routinely inspected to check for physical damage because there is often no earthing with systems that have double insulation
Residual current device (RCD)
Principles
Difference means current is being diverted (maybe through direct contact with person)
Reacts quickly to minimal current differences
Switches off supply where it detects a difference between current flowing in & out of it
Reduces the effect of an electric shock
Designed to protect humans on contact with electrical cicuit
Advantages
Very sensitive to small changes in current
Easy to test & reset
Limitations
Does not provide over-current protection like a fuse
Can cause repeated trips if there is a fault (leading to workers trying to disable them)
Reduces low voltage systems
Principles
Commonly achieved by the use of step down transformer
Another method is the use of battery power
Advantages
Low voltage systems are generally much safer
Limitation
Reduced voltage systems are not practical for many industrial processes
Use of competent persons
Anyone who undertakes electrical work must be competent & have:
Experience of electrical work (similar to that being undertaken)
Understanding of hazards & controls
Knowledge of electricity
The ability to recognise dangerous situations
Safe systems of work - Live electrical work
Protection of the work area from other hazards (e.g. vehicles)
Isolation of non-essential conductor in the vicinity
Restriction of work area to these competent people
Use of suitable, insulated test equipment & tools
At least 2 competent people present
Adequate lighting & clear space to work
Permit-to-work permit system
First aid immediately available
Justification as to why there is no alternative to working live
Safe systems of work - Isolation
Isolation procedure often known as lock out/tag out (related to permits-to-work)
Lock involves use of padlock to isolate starting mechanism of machine
Isolation requires disconnection at the primary isolation mechanism for equipment circuit
Tag is a sign stating that unauthorised start must not be carried out
Simply switching off is inadequate
Safe systems of work - Located buried services
Use of CAT scanners by trained personnel
Hand digging until buried cables are located
Use of detection device such as cable avoidance tool (CAT scanner)
Supporting pipes which have had earth moved around them
Use of map/drawings detailing the location of buried services
Safe systems of work - Protection from overhead cables
Permit-to-work
Barriers & goal posts to prevent contact with machinery
Sheathing the lines if they must remain live
Non-conductive equipment near power lines
Isolating overhead lines to make them dead
Signs which clearly mark danger zones
Carrying out as much work as possible away from power lines
Emergency procedure following an electrical incident
Do not touch the casualty
Remove the power
Shut off the power, if possible
Assess the casualty & commence first aid (resuscitation if necessary)
Summon help
Keep the casualty under observation & treat secondary injuries
Assess the situation
Inspection & maintenance strategies - User checks
Carried out by the user of the equipment. Inspections should identify:
Wet or dirty equipment
Burn marks or discolouration
Overloaded sockets
Loose parts or screws
Faulty or ineffective switches
Loose or damaged sockets or switches
Bare wires
Lack of circuit protection (RCD)
Taped or other inadequate cable joints
Evidence of unauthorised repairs
Damaged plugs ( cracked casing, bent pins)
cable trapped under furniture
Abrasions & cracks in insulation cable
Vent holes blocked
Inspection & maintenance strategies
Formal visual inspection
Carried out by competent person (electrician)
More in-depth tan a user check (e.g. opening casing to check quality of earthing)
Combined inspection & testing
Involves testing the circuits specifically (visual inspection does not do this)
Testing carried out using portable appliance meter (PAT testing)
More in depth than formal visual inspection
Carried out by competent person (electrician)
Factors to consider when deciding frequency of testing
Whether equipment is hand-held
Manufacturer's recommendations
Type of equipment
Initial integrity & soundness
Age
Environment in which the equipment is used
Likelihood of damage
Frequency of use
Duration of use (intensity)
Past modification or repairs
Records of inspection & testing
Labels on equipment or fixed installation should display test date & status
Regular monitoring to ensure inspection & testing is being carried out
Records should be kept of all formal visual inspections & all combined inspection & testing
Portable appliance testing
Advantages
Ensures compliance to legal standards for maintenance & testing
Could highlight particular hazards with certain types of equipment
Detects faults which will not be identified by visual inspection
limitations
Provides proof of safety only at the time of testing
Cannot be carried out on some types of equipment