Electrical Physics

Question 1

What are active wires?

Answer 1

Active wires passes the current from the distribution line through a switchboard which holds a mains switch, a meter and circuit breaker that protect the various distribution circuits within the house. It is the active wire that carries the 240v potential difference which operates your electrical appliances and is the potentially dangerous wire.

Question 2

What is the neutral wire:

Answer 2

The neutral wire connects every power point in your house to a piece of metal called neutral bar. The neutral bar is in turn connected to the earthing electrode, giving the neutral wire and earth wire zero potential to the earth.

Question 3

Most Dangerous Path for current to pass your body:

Answer 3

The most dangerous path for current is across since the most likely to affect the heart. The lower the resistance the greater the current will pass through the body and the greater danger to life. Skin resistance is lower when the skin is wet (or broken by a cut /abrasion), so situations

Question 4

There are several features of a mains installation which contribute to safety:

Answer 4

1. Fuses and circuit-beakers
   2.Residual current devices
   3.Earthing and double insulation

Question 5

Fuses:

Answer 5

Faults in electrical wiring can cause short circuits. These cause large amounts of current to flow, which can cause over heating and fires. Fuses are wired in series with active wires. If excessive current flows the fuse will melt breaking the circuit. The fuse must be replaced every time it melts.

Question 6

Circuit Breaker:

Answer 6

If the current exceeds the predetermined limit, an electromagnet triggers a switch which opens the circuit. Unlike fuses, circuit breaker can be reset.

Question 7

Residual Current Devices:

Answer 7

An RCD activates a circuit breaker if a fault or accident results in the grounding of a ‘live wire’ and the current flowing through the neutral wire. If there is a difference between the two, this is an indication that current is ‘leaking somewhere’ in the building. If the difference is detected the RCD triggers a circuit breaker.

Question 8

Earthing and double insulation:

Answer 8

Many appliances have metal parts, it is possible for a fault to occur which brings the active wire in contact with the metal, leading to an electric shock. Because of this metal parts are earthed so that if the metal becomes live the current will flow harmlessly into the ground through the earth wire, instead of through the user.