C8 electricity Flashcards
Differences between high and low voltage
Ohms law
High Excessive of 1000v ac 1500v Dc Low 50v -1000v Ac 120-1500Dc Less 50 very low
V= IxR I= V/R R= V/I
Electric shock effects on the body
Pain Muscle contractions Burns-internal Cardiac arrest Respiratory Failure VF
Secondary effects
Involuntary throwing back arms
Shock startles , falls from height
Factors affecting severity of shock on body
Duration- time passed through body 100ma -1 second = dead
Voltage/ current increase one = other
Passage through body- direction/ heart
Resistance/ impedance wet hands etc
Frequency = DC / AC
Direct/ indirect shock
Causes of fire by electricity
Damage mechanical
Damaged insulation
Overheating- Overloaded conductors
Heating of flammable materials close to electric equipment
Ignition of flammable vapour by elect
Static what is it and controls
Build up of electrons on poor conductors of electricity. Speed of separation of materials
Rubbing of ballon on jumper
Controls
Earthing Ventilation- reduce atmosphere below lel Increase conductivity Ionisation Inneting - atmosphere
Legislation and testing
Duty holders
Regs
Testing
Types
Frequency
E@W regs 1998
IET 17ed
Duty holders
Employers
Employees
Testing
User checks persons using looking for faults
Visual formal, competent persons, recorded formal and systematic manner
Combined inspection and tests
Testing and visual to if faults
Earthing faults, deteriorated insulation,
Records
Logs kept, types of tests, inventory of equipment
Frequency of tests depends on Type of equipment / hand held Manufacturers recommendations Age Working environment Frequency of use Abuse to equipment Repairs
Aspects of electric systems
Control measures
Strength and capability of equipment- not to be exceeded
Insulation, protection and placing conductors
Covered with suitable insulation materials and protected
Reducing risks of shock
Likelihood iits ssow ptw system design
Consequences current reduction devices
Excess current protection
Fuses
Metallic strip, melts with heat and designed to cut off power supply
Circuit breakers
Can be reset, cut out when excess current detected
Rcd’s
Measure current flowing in live and neutral and trip the circuit if short circuit earth detected
Cutting off and isolating supping
Cutting off - depriving the equipment of power
As above but additional step of barrier to prevent inherent turning on
Ventilation and lighting and access
Adequate space and lighting where there is danger.
Controls
Technical
Double insulation
Protective systems- fuses, rcds, earth free zones
Reduced voltage systems - 55 v direct contact
Procedural Isolation Ra Ssow Ptw Maintenance Testing
Behavioural Its Log tag Competence PPE
SSOW live working
Circumstances permitting live working
Precautions of live working
Unreasonable for live part to be dead
Reasonable for person to work on or near live conductors
Precautions Trained competent persons Information Suitable, tools equipment and ppe Accompanied working Restricted access
Safe systems of work on dead installations
Permits should include
Tech
Earth equipment
Disconnect equipment
Isolate securely
Pro Plan job Prove test instruments Prove equipment is dead Re prove trest equipment
Beh
Signs and notices
Understanding of job
Additional precautions
Permits contain Supervisor of work, permit issued Id equipment made dead and location Location if isolating points Location of earth connections Location of warning notices and safety locks Description of work Hazards Further precautions
SSOW and PTW Work on high voltage systems procedures
High voltage must be a ptw
PTW only on systems made dead
Precautions and nature of work
Restricted access to high voltage areas only persons in writing
Physical barriers fences, locked access interlocking
Safe work on overhead / underground powerlines
Overhead accessible by roofs, platforms elevated platforms scaffolding
Precautions to avoid contact
Three possible categories are:-
No work or passage beneath lines, ground level barriers to close approach to lines
Passage of plant beneath lined passage width restricted to no more than 10m and preferably to right angles with the lines, defined by fencing with goal posts at each end.
Work carried out beneath lines with barriers, goalposts, warning notices erected, and safe clearance distance or horizontal barrier of insulting material erected to form a roof over work area.
Safe working with Underground cables
High voltage glove working and live line overhead working
Hazardous because they are concealed, close to surface, sometimes occur in unexpected locations and often poorly protected
Damage usually during excavations
A SSOW incorporating the:-
Location
Cable loc plans
Cable loc devices
Safe digging practices
IITS
Live working to replace insulators, repairs to conductors. The EAWR requires:-
Justification for work and assurance it can be carried out using acceptable live working precautions
Live line work can involve:-
High voltage glove work
Long stick ops
Short stick ops
Portable electric equipment
What leads to accidents
Elect risks portable appliances
Hazards/ Controls
Testing
Incorrectly made connections
Damaged insulation
Exposed conductors
Insulation failure- leaking current and live metalwork
Servicing without disconnecting
Misuse
Unauthorised equipment brought into workplace
Risks
Generators
Keep dry, don’t use in wet conditions
Insulted cables sufficient current capacity
Plug appliances straight into generator
Never plug generator into building supplies
Arc welding
Connection to power and work piece as direct as possible
Insulated cables
Endure earth clamp as to work as possible
Hazards Use- Unsuitable equipment Defective equipment Misuse of equipment Inadequate maintenance
Controls Earthing all exposed metal parts All insulted casings Double insulation Reduced voltages Sensitive earth leaked protection
Testing
HsG 107
System for maintenance of portable equipment
Identify portable equipment that needs to be maintained and where and how its used
Decide actions for unauthorised equipment
Training on user checks
Formal visual inspection system
Written guidance on inspection
Frequency of inspections
Competent person to conduct combined inspection snd test
