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points in the circuit. Fuses are rated in amperes and the rating must
be correct so that if there is an overload the fuse will melt and
break the circuit before any damage to the circuit wiring or the
equipment occurs. If a fuse blows the correct manual switch must
be switched off and the fault rectified before replacing the fuse.
When a fuse is changed the correct rating must be used. It is
dangerous and can be expensive to fit a replacement fuse with a
higher rating.

Automatic Trip Switches
Automatic trip switches are often fitted to electrical devices
to protect them from overloads. Usually, they are terminal
switches that break the circuit when an overload causes a bi-metal
strip in the switch to bend. These switches have a re-set button,
which resets the trip switch and completes the circuit. If the circuit
is broken because of an increase in current, the switch cannot be
re-set immediately. The bi-metal strip needs time to cool (approx.
30 seconds) before the switch can be re-set.

Connecting Plugs
A lamp is connected with the switch open. The lamp holder
can only become live when a fault occurs in the insulation, which
is not isolated by the switch.
When plugs for operating electrically powered hand tools are
connected, the minimum rating for the connector must not be
exceeded.

Step 4

Are these statements true or false? Correct the false ones.

1. Electric circuits must be protected against current overloads.
2. An increase in current causes heat to be generated in
conductors.
3. Burning insulation can be caused by fuses.
4. Defective circuits must be isolated from the supply.
5. Fuses can be replaced immediately after melting. Use a

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