Datasheet

AMC1203
SBAS427C –FEBRUARY 2008– REVISED JUNE 2011 www.ti.com
ISOLATION GLOSSARY
Creepage Distance: The shortest path between two the leakage current produces an overvoltage at the
conductive input to output leads measured along the site of the discontinuity, and an electric spark is
surface of the insulation. The shortest distance path generated. These sparks often cause carbonization
is found around the end of the package body. on insulation material and lead to a carbon track
between points of different potential. This process is
known as tracking.
Insulation:
Operational insulation—Insulation needed for the
correct operation of the equipment.
Basic insulation—Insulation to provide basic
protection against electric shock.
Clearance: The shortest distance between two
conductive input to output leads measured through air Supplementary insulation—Independent insulation
(line of sight). applied in addition to basic insulation in order to
ensure protection against electric shock in the event
of a failure of the basic insulation.
Double insulation—Insulation comprising both basic
and supplementary insulation.
Reinforced insulation—A single insulation system that
provides a degree of protection against electric shock
equivalent to double insulation.
Input-to Output Barrier Capacitance: The total
Pollution Degree:
capacitance between all input terminals connected
Pollution Degree 1—No pollution, or only dry,
together, and all output terminals connected together.
nonconductive pollution occurs. The pollution has no
Input-to Output Barrier Resistance: The total
influence on device performance.
resistance between all input terminals connected
Pollution Degree 2—Normally, only nonconductive
together, and all output terminals connected together.
pollution occurs. However, a temporary conductivity
Primary Circuit: An internal circuit directly connected
caused by condensation is to be expected.
to an external supply mains or other equivalent
Pollution Degree 3—Conductive pollution, or dry
source that supplies the primary circuit electric power.
nonconductive pollution that becomes conductive
Secondary Circuit: A circuit with no direct
because of condensation, occurs. Condensation is to
connection to primary power that derives its power
be expected.
from a separate isolated source.
Pollution Degree 4 – Continuous conductivity occurs
Comparative Tracking Index (CTI): CTI is an index
as a result of conductive dust, rain, or other wet
used for electrical insulating materials. It is defined as
conditions.
the numerical value of the voltage that causes failure
by tracking during standard testing. Tracking is the
Installation Category:
process that produces a partially conducting path of
Overvoltage Category—This section is directed at
localized deterioration on or through the surface of an
insulation coordination by identifying the transient
insulating material as a result of the action of electric
overvoltages that may occur, and by assigning four
discharges on or close to an insulation surface. The
different levels as indicated in IEC 60664.
higher CTI value of the insulating material, the
I: Signal Level: Special equipment or parts of
smaller the minimum creepage distance.
equipment.
Generally, insulation breakdown occurs either
II: Local Level: Portable equipment, etc.
through the material, over its surface, or both.
III: Distribution Level: Fixed installation.
Surface failure may arise from flashover or from the
progressive degradation of the insulation surface by
IV: Primary Supply Level: Overhead lines, cable
small localized sparks. Such sparks are the result of
systems.
the breaking of a surface film of conducting
Each category should be subject to smaller transients
contaminant on the insulation. The resulting break in
than the previous category.
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