3005 MEN, SELV, PELV Electrical Protection 2

What problem does earth leakage not cause?

• Reduces the efficiency of the installation due to list energy

• Reduces the safety factor and increases the chance of electric shock

• Causes nuisance tripping of MCB's

• Could cause a fire in flammable situations

What does not constitute basic electrical protection?

• Extra low voltage

• Protection by insulation

• Protection by RCD's

• Protection by obstacles

Which of the following does not provide fault protection?

• Electrical separation

• Class 1 equipment

• Automatic disconnection

• Fault current limiting

Electromechanical energy is when electrical energy is converted into ___________ energy.

• Electrical

• Heat

• Kinetic

• Mechanical

What is the prospective short circuit current of a 2KVA 1 phase transformer with an impedance of 6%

• 100 Amps

• 173.9 Amps

• 144.83 Amps

• 121.73 Amps

Answer explanation

2KVA/230v = 8.69 Amps

8.69 x (100/6) = 144.83 Amps

The current uses the body as a high resistance path to earth and it flows through the body

• True

• False

The standard sets out 4 ways to provide fault protection. What is not one of the 4 ways from the list below?

• Automatic disconnection

• Electrical separation

• Class 1 equipment

• Fault current limiting

Impedance is the overall opposition to current flow in an AC circuit. What does not form part of the total impedance?

• Resistance

• Capacitive reactance

• Inductive reactance

• Resistive reactance

The impedance of a circuit needs to be kept low as possible so that .....

• large amounts of voltage will around the fault loop

• the touch voltage is as high as possible to trip the protective device

• large amounts of current will flow back to earth

• large amounts of current will flow around the fault loop

Automatic disconnection of the supply is intended to limit the touch voltage arising between conductive parts during a fault.

• True

• False