Page 82 - Physics_Form_2
P. 82
Physics for Secondary Schools
wire has much lower resistance than a type of distribution board that distributes
the bulbs. This results in a large electricity from the main supply to separate
current flow, hence, the melting of a circuits. From the consumer unit, the cables
fuse wire. branch into several parallel circuits which
carry current to the various parts of the house.
A circuit breaker like the ones There are two methods of wiring a house from
FOR ONLINE READING ONLY
shown in Figure 2.47 is a type of the main switch: the ring and tree systems.
switch that cuts off the flow of
current when the current in a circuit Ring main system. In many houses, the main
exceeds a specific value. It operates sockets are connected to a ring main. This
by opening the circuit in the event cable begins and ends at the consumer unit. It
of excess current. Unlike a fuse, has live, neutral, and earth wires, each forming
a circuit breaker can be reset once a ring around the house or part of the house.
the current in a circuit has returned In a circuit, the current has two parts, so thin
to normal. However, like a fuse, a cables can be used. The sockets usually have
circuit breaker is connected in series
with the circuit it controls. a 30 A fuse at the consumer unit. Figure 2.48
shows a typical ring main circuit.
In a circuit breaker, switch contacts
are held closed by a latch mechanism
that releases the contacts quickly to
open the circuit.
Junction
box
Live
Neutral
Earth
Customer unit
Figure 2.47: Examples of circuit-
breakers
Figure 2.48: Consumer unit and a ring main in a
house
Domestic wiring
The power company connects The tree system method uses a cable from the
power to a house up to the meter main switch to the distribution box as shown in
and leaves cables to be connected to Figure 2.49. Of these two methods of wiring,
the consumer unit where the house the ring system is more convenient for wiring
wiring starts. A consumer unit is modern houses than the tree system.
76
Student’s Book Form One
Physics Form 2 Final.indd 76 25/10/2025 10:26
