The voltage, which may be applied to a terminal, depends on technical specifications, installed conditions and also, of course, on the dimensions and insulating materials of the terminal.
DIN VDE 0110-1 is essentially aimed at the technical committees, which draft such standards. In the case that no clearance in air or creepage distances are specified in the relevant standards, or even that there is no relevant standard, this basic safety standard can be applied, but places considerable responsibility on the user. The rated voltages in the WECO catalogue are based on a quoted pollution degree. The rated impulse voltages are stated for the corresponding clearances in air at altitudes of less than 2000 m above sea level.
Clearance in air and creepage distances:
Air clearance dimensions must be measured in that way, that they withstand the required switching impulse voltage. They should be selected according to Table 2. The following influencing factors should be taken into account: switching impulse voltage requirements for functional insulation, basic insulation, supplementary and uprated insulation, electric field conditions, the altitude of the location and the micro-environment. Mechanical influences such as vibration and effective forces may necessitate bigger clearances in air.
Creepage distances must be selected from Table 4. The following influencing factors must be taken into account: voltage, micro-environment, direction and position of the creepage distances, shape of the insulant surface, the insulant itself and the duration of electrical stress. For precise information, see the product standards and DIN VDE 0110-1.
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Pollution Severity Level:
The micro-environment determines the influence of pollution on the insulating material. However, the macro-environment must also be taken into account. To determine clearance in air and creepage distances, the following four levels of pollution severity for the micro-environment have been defined: |
Pollution Severity Level 1
No pollution or only dry, non-conductive pollution occurs. The pollution has no influence.
Pollution Severity Level 2
Only non-conductive pollution occurs. However, occasional temporary conductivity must be expected as a result of moisture condensation.
Pollution Severity Level 3
Conductive or dry pollution develops. Pollution severity level 3 is also reached in case non-conductive pollution becomes conductive by moisture condensation.
Pollution Severity Level 4
Impurities in the form of conductive dust, rain or snow result in permanent conductivity.
Insulant:
Insulants are divided into the following four groups, according to their comparative tracking index (CTI)
| Insulant I: |
600 ≤ CTI |
| Insulant II: |
400 ≤ CTI < 600 |
| Insulant IIIa: |
175 ≤ CTI < 400 |
| Insulant IIIb: |
100 ≤ CTI < 175 |
Part 1 of DIN VDE 0110 contains international standard IEC 664-1; 1992
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