Page 20 - Electrical Safety of Low Voltage Systems

2 Chapter One

1.2.3 Class I Equipment
Equipment outfitted with basic insulation and bonding terminals;
automatic disconnection of supply can be carried out as protection
against electric shock in the case of failure of the basic insulation.

1.2.4 Class II Equipment
Equipment outfitted with a double insulation, consisting of basic in-
sulation plus supplementary insulation, or a reinforced insulation.

1.2.5 Class III Equipment
Equipment in which protection against electric shock solely relies on
supply at safety extra-low voltage. Thus, the extra safety features built
into Class I and Class II appliances are not required.

1.2.6 Direct Contact
Contact with parts of the installation normally live.

1.2.7 Indirect Contact
Contact with metal parts not normally live (e.g., exposed-conductive-
parts), but energized under fault conditions. (The basic difference be-
tween the definitions of direct and indirect contact is the presence,
between the live part and the person, of a metal enclosure.)

1.2.8 Disconnection of Supply
Protection against indirect contact may be carried out by automatic
disconnection of supply. A protective device shall automatically dis-
connect the supply to the faulty circuit or equipment so that a prospec-
tive touch voltage exceeding 50 V a.c. r.m.s. (or 120 V ripple-free d.c.)
does not persist for a time sufficient to cause a risk of harmful physi-
ological effect in a person.

1.2.9 Exposed-Conductive-Part (ECP)
ECP is a conductive part, forming part of electrical equipment, which
can be touched (even if out of reach), and which is not live, but which
may become live when basic insulation fails. A conductive part that
can be energized just because it is in touch with an ECP shall not
be considered an ECP. Sometimes ECPs are referred to as noncurrent-
carrying metal parts.

1.2.10 Extra-Low Voltage
Voltage supplied from a source that does not exceed 50 V between
conductors and between conductors and earth.