Session 3 Symptoms of electrical faults.

Regarding Electrical Faults every installation shall be divided into circuits as necessary to:

• avoid hazards and minimise inconvenience in the event of a fault.

• reduce the cost of the job.

• protect circuits against overload fault.

• protect circuits against mechanical damage during a fault.

Which of the following would be a common example of a loss of supply?

• Smell of burning coming from a two-way switch.

• The supply company’s protective devices operating.

• The sound of arcing coming from a socket outlet.

• Loose cpc in a consumer unit in a domestic house.

Which of the following would be classed as a overload?

• Insulation breakdown

• Arcing at a two-way switch.

• Motor starting current not accounted for on motor circuit.

• Breaking of live circuit by nail or similar.

Which of the following could lead to an earth fault or short circuit?

• Faulty switch.

• Faulty socket outlet.

• Extra loads places on an existing circuit or installation

• Breaking of live circuit by nail or similar.

Which of the following would not be classed as causing a high resistance?

• Poor or loose connections

• Cross-sectional area of cable too large.

• Cross-sectional area of cable too small.

• Long cable runs.

When equipment that contains inductors and capacitors are regularly switched then a short-term voltage spike is injected onto the system. What term is this known as?

• Overload

• Transient voltage

• Earth fault.

• High resistance joint.

Which of the following would best describe a open circuit?

• Cables with a low insulation resistance value.

• Cables connected with a torque screwdriver.

• Cables not connected properly.

• A low R1+R2 reading.

An immersion heater element has a direct fault to earth. Using an insulation resistance tester the fault will show itself as

• an infinity reading between L and N

• a zero reading between L and N

• a zero reading between L and E

• an infinity reading between L and E

A fault between the phase conductor and the surrounding metalwork of an appliance may not operate a protective rewirable fuse if the

• Zs value is too high

• Ze value is less then 0.5 ohms

• Ze value is higher that 0.5 ohms

• Zs value is too low

An insulation resistance test is carried out on an MI cable. A low insulation resistance value is recorded. The reading is probably caused by

• unsuitable environment

• a short circuit caused by twisted conductors

• unsuitable cable

• moisture absorbed into the insulation