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I2679-4.0 en
2.5
Protection and isolation
2.5.1
Measurement categories
The international standards for test equipment safety are the IEC 61010-1
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and the IEC 61010-2-030.
IEC 61010-1 defines three overvoltage categories (CAT II, CAT III, and
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CAT IV) on the power supply side of an instrument.
IEC 61010-2-030 defines three measurement categories (CAT II, CAT III,
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and CAT IV) on the measurement input side of an instrument, for
measurement inputs which can be directly connected to mains.
All measurement inputs, which are not specified to be connected to mains,
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have no CAT rating and are referred to as O (like Others).
Categories according to IEC 61010-2-030:2010
Electrical equipment, specifically measurement tools can according to IEC
61010-2-030:2010 be assigned into 4 categories. These measurement
categories are indicated with the terms O (previously CAT I), CAT II, CAT III
and CAT IV. Originally these categories are used to indicate the overvoltage or
surge voltage that is likely to occur and can be sustained by the equipment.
Actually the category indicates the amount of energy that can be released in
the event of a short circuit. A higher category number indicates a higher energy
level that can occur and can be sustained by the equipment.
O (Other) (previously referred to as CAT I): This category is for measurements
not directly connected to mains. Think of measurement of; signal levels,
regulated low voltage circuits or protected secondary circuits. For this category
there are no standard over voltage or surge impulse levels defined.
CAT II: This category is for measurements directly connected to low-voltage
mains. Think of measurement of; mains sockets in household applications or
portable tools. This category is expecting to have a minimum of three levels of
over current protection between the transformer and connection point of the
measurement. (See Figure 2.1).
CAT III: This category is for measurements directly connected to the distribution
part of a low-voltage mains installation. Think of measurement of; circuit
breakers, wiring, junction boxes etc. This category is expecting to have a
minimum of two levels of over current protection between the transformer and
connection point of the measurement. (See Figure 2.1).
CAT IV: This category is for measurements directly connected to the source of
a low-voltage mains installation. Think of measurement of; over current
protection devices, ripple control units etc. This category is expecting to have
a minimum of one level of over current protection between the transformer and
connection point of the measurement circuit. (See Figure 2.1).
GEN5i
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