Page 399 - IGC BOOK

Reduced Voltage system

Reducing the supply of voltage to lowest
voltage to operate the equipment. A nominal
line to line voltage does not exceed 110V, this
is achieved through a simple transformer,
often centre tapped to earth so that the
maximum voltage between a live conductor
and earth (the most common cause of electric
shocks from equipment) is limited to 55V.

Temporary and handheld lighting can be provided at 12, 25, 50 or 110 volts.

Advantages Disadvantages
• Redcues severity caused by electricity • Requires transfomer to step down the

• Easy to identify – color codes for the cabels voltage.
• Needs protection with RCD

Residual Current Devices

Residual current device (RCD), is a device that breaks
the circuit on fault or any leaking current. RCD detects
a difference of 30mA / 30ms. RCD does not prevent
people from electric shock, but they are able to limit
the duration of electric shock through rapid
disconnection electrical supply when an electric shock
takes place. In the event of trip, the fault in the system
must be rectified before trip on, RCD’s with test button
should be checked frequently to ensure that the
mechanism works correctly.

Advantages Disadvantages
• Rapid disconnection • No overload protection
• Protect people from electric shock • Requires regular testing and maintenance.

• Difficult to defeat system. • Frequent tripping due to mechanical
• Prevetns reset if there is fault. failure.

Double Insulation

Double insulation Protect people from exposing to live conductors.
Double insulations have two layers of insulating materials such as
sheathing around the conductors. Equipment without earthing are
usually double insulated, marked with ‘double square’ symbol to highlight
that the conductors are double insulated.

ENSIGN | Unit IG2 – Element 11 – Electricity 10