EPC 23 - Control & Protection Requirements Flashcards
What are the THREE main ratings applied to circuit breakers?
Maximum operating voltage,
Full load or continuous current rating,
Breaking capacity.
In relation to “protection against overload current”, what is meant by the term coordination in a Circuit protection system? (Give the Wiring Rules Clause Number).
The current rating of the circuit breaker is equal to or greater than the load current, but equal to or less than the conductor current rating.
Clause 2.5.3.1 or Appendix B.
If the maximum safe working current for wiring is exceeded, and the protection is inadequate or does not operate, how will the wiring be affected?
Overheating of the wiring and magnetic stress.
Explain the term inverse time characteristic as applied to fuses and circuit breakers.
The higher the fault current, the quicker the response time to operate.
What limits the value of short circuit current when a short occurs in a final sub-circuit?
The impedance of the circuit wiring.
What is the basic operational difference between a switch and a circuit breaker?
A circuit breaker automatically operates under fault conditions, where as a switch is manually operated.
What effects can it have on an electrical circuit if the maximum safe working current is exceeded?
- Overheating,
- Damage caused by arcing,
- Damaging effect of magnetic stresses,
- Physical damage to cables and components.
Which clause in AS/NZS 3000 specifies the requirements for coordination between conductors
and protective devices?
AS/NZS 3000 Clauses 2.5.3.1 and B3.2.
Which TWO factors govern the value of current which can flow in a circuit if a ‘short circuit’ or ‘bolted fault’ occurs?
The supply voltage and the circuit fault loop impedance. = V+Zs
When providing protection against indirect contact in a 230V installation, what is the maximum permissible disconnection time for final sub-circuits that supply 10A socket outlets? (Give the Wiring Rules Clause Number).
0.4 seconds (400ms).
AS/NZS 3000 Clause 1.5.5.3(d) (i).
When providing protection against indirect contact (fault protection), what is the maximum permissible disconnection time for a final sub-circuit supplying a fixed-wired air conditioning unit? (Give the Wiring Rules Clause Number).
5 seconds.
AS/NZS 3000 Clause 1.5.5.3(d) (ii).
What is the maximum internal fault-loop impedance for a 230V final sub-circuit that supplies 10A socket outlets, and is protected by a 16A Type C circuit breaker? The supply is not available. (Give the Wiring Rules Clause Number).
1.2 Ohms (Table 8.2).
List the internal and external parts of an MEN system which comprise the ‘fault-loop’ according to AS/NZS 3000. (Give the Wiring Rules Clause Number).
Protective earth, Neutral-return path, Transformer neutral, Transformer winding, Associated active to fault.
AS/NZS 3000 Clause B4.4.
