Protective devices Flashcards
In an electrical system what are the two main types of fault?
Overcurrent
Earth leakage
What are the two different types of overcurrent
Overload current
Fault Current
What is the definition of an overcurrent
A current exceeding the rated value. For conductors this is the current carrying capacity.
List 3 overcurrent protective devices?
Fuse
Circuit Breaker
RCD
What is the definition of an overload current
An overcurrent occuring in a circuit which is electrically sound.
Why do overload currents occur?
Overload currents occur when a circuit is abused e.g. to many appliances plugged into socket outlets or badly designed/modified
Define a fault current
A current resulting from a fault
Define a ‘fault’
A circuit condition in which current flows through an abnormal or unintended path.
Define earth leakage
Referred to as protective conductor current.
Electric current appearing in a protective conductor such as leakage current or resulting from an insulation fault
List some protective devices used for earth leakage current
Fuse
Circuit Breaker
RCD - Residual current divider
RCBO - Residual current operated circuit breaker
What are the effects from AC current on a persons? Ar 1 mA
10-15mA
30mA
1mA - A slight tingle
10-15mA - Can cause powerful muscle contractions
30mA - Can cause cardiac arrest
What is a BS3036
A semi-enclosed fuse, referred to as re-wire-able fuse
A fuse wire is connected betweem two blades and will melt causing circuit to break
List 3 advantages of BS3036
Simple to check if blown
Low cost to replace fuse element
No moving parts
List Disadvantages of BS3036
Danger of being repaired with wrong wire
Deteriorate with age
Circuit cannot be quickly restored
Cannot break large fault currents
