Rating of Clearance and Creepage Distances
nach DIN EN 60664-1 (VDE 0110-1)
DIN EN 60664-1 (VDE 0110-1), Table F.4 (excerpt)
Creepage distance for the avoidance of the failure by tracking
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|F.2||DIN EN 60664-1 (VDE 0110-1), table F.2 (extract) Clearance for transient overvoltages|
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Overvoltage category III:
Electrical equipment in firm installations and for such cases in which special demands are made against the reliability and the availability of the electrical equipment, e.g. switches in firm installations and devices for industrial use with continuing connection to the firm installation.
Overvoltage category II:
Energy using electrical equipment, which is energised by a firm installation e.g. household appliances, portable tools and other domestic appliances as well as similar devices.
Overvoltage category I:
Electrical equipment for the connection to electric circuits, in which measures are taken for the delimitation of the transient overvoltages to a suitable low value, e.g. devices with electronic circuits and appropriate protection level.
Degree of contamination
The micro environment determines the influence of the contamination on the isolation. However the macro environment must be considered with the view of the micro environment.
Resources to achieve a reduction of the contamination on the regarded isolation can be planned by the effective employment of casings (housings), encapsulations or hermetic sealings.
The influence of the contamination is considered with the calculation of air and creepage distances by degrees of pollution.
DIN EN 60664-1 (VDE 0110-1), Table F.1 (excerpt)
Rated impulse voltages for electrical equipments, which are energised directly by a low-voltage system
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Four degrees of contamination levels are defined for the micro environment:
Contamination level 1
No contamination or only dry, non-conductive contamination occurs. The contamination has no influence.
Contamination level 2
Only non-conductive contamination occurs. However, occasional temporary conductivity must be expected as a result of moisture condensation.
Contamination level 3
Conductive contamination occurs; dry, non-conductive contamination which becomes conductive as a result of moisture condensation may also occur.
Contamination level 4
Impurities in the form of conductive dust, rain or humidity result in permanent conductivity.
DIN EN 60664-1 (VDE 0110-1) divides the insulants according to their CTI values in four groups. These are:
|Insulant I:||600 ≤ CTI|
|Insulant II:||400 ≤ CTI < 600|
|Insulant IIIa:||175 ≤ CTI < 400|
|Insulant IIIb:||100 ≤ CTI < 175|
The check numbers of the tracking must be determined according to IEC 60112 at an examination body using test solution A. The check number of the tracking is used as a proof of the creepage characteristics of insulants.