Page 32 - Electrical Safety of Low Voltage Systems

Fundamentals of Electrical Safety 15

FIGURE 2.5 Volume out of reach.

We conventionally deem out-of-reach energized objects placed
outside of the volume defined by the reach of the person’s arm. The
horizontal arm’s extent is conventionally assumed to be 1.25 m, but as
the contact can also occur in the overhead direction, the average height
of persons must be included. Therefore, the conventional length of
2.5 m from the floor is also considered arm’s reach. The extent of
arm’s reach is to be measured from the obstacle (Fig. 2.5).
Skilled persons are deemed safe as long as exposed energized
parts are in the volume out of reach (i.e., outside of the dotted line).
If persons normally handle long conductive items (e.g., tools, lad-
ders, etc.), larger clearance distances must be considered to take into
account the additional risk due to their length so as to provide the
same level of safety.

2.2.4 Additional Protection by Residual Current Devices
Residual current devices (RCDs) are also referred to as residual cur-
rent operated circuit-breakers (RCCBs) or ground-fault circuit interrupters
(GFCIs). RCDs with operating current I dn not exceeding 30 mA
are additional means of protection against direct contact. When
they are used in households and similar environments, nontrained
people should be able to easily operate them.