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Pollution Degrees Dimensioning of Clearances
Pollution factors are all solid, liquid or gaseous foreign matter which may reduce the per DIN EN 60664-1/ VDE 0110,
dielectric strength or the specific surface resistance. Factors are divided into 4 classes
based on expected environmental conditions: Part 1, Table F.2.
Select the minimum clearances in accor-
dance with the rated surge voltages and
Examples of pollution pollution degree. For the operating life of
degrees for assigned the equipment, do not go below these
areas: minimum clearances.
Pollution degree 1: No pollution, or only dry, non- Open, unprotected insula- Table F.2 contains a list of information for
conductive pollution occurs. ted equipment in air-condi- Case A, the inhomogeneous field and for
The pollution has no influence. tioned or clean, dry rooms. Case B, the homogeneous field.
This involves an electric field with essen-
Pollution degree 2: Only non-conductive pollution Open, unprotected insula- tially constant (Case B) or non-constant
occurs; occasional, temporary ted equipment in occupied (Case A) voltage gradients between the
conductivity caused by con- areas, shops, laboratories,
densation can also be expec- mechanical workshops and electrodes.
ted. medical rooms. Equipment with a clearance in accor-
dance with Case A, in other words
rated for the most unfavorable case,
can be employed without evidence
Pollution degree 3: Conductive pollution occurs, or Open, unprotected insula- of surge voltage testing.
dry, non-conductive pollution ted equipment in industrial, Equipment whose clearances are dimen-
occurs which will become con- business and farming are-
ductive due to condensation. as, e.g., unheated rooms, sioned acc. to Case B, or between A and
workshops and boiler B, requires verification by the surge volt-
rooms. age test.

Pollution degree 4: The pollution generates persis- Open, unprotected insula- The clearances shown in Table F.2 are
tent conductivity caused by ted equipment for outdoor applicable for an installation height of up
conductive dust, rain or wet use. to 2000m above sea level.
conditions.
Values for clearances above 2000m must
Table F.2 - Clearances to Withstand Transient Overvoltages be multiplied by a high correction factor
DIN EN 60664-1/ VDE 0110, Part 1 in accordance with Table A.2.
Minimum clearances in air up to 2000 m above sea level
Required Case A Case B
impulse (inhomogeneous field, see 3.15) homogeneous field (see 3.14)
withstand
voltage 1)5) Degree of pollution 6 Degree of pollution 6
1 2 3 1 2 3
kV mm mm mm mm mm mm
0.33 2) 0.01 0.01
0.40 0.02 0.02
0.50 2) 0.04 0.2 3)4) 0.04
0.60 0.06 0.8 4) 0.06 0.2 3)4) 1) This voltage is
0.80 2) 0.10 0.10 – for functional insulation: the maximum surge voltage
1 0.15 0.15 0.8 4) expected to occur across the clearance (see 5.1.5);
1.2 0.25 0.25 0.2 – for basic insulation directly exposed to or significantly
influenced by transient overvoltages from the low-volt-
1.5 2) 0.5 0.5 0.3 0.3 age mains (see 4.3.3.3, 4.3.3.4.1 and 5.1.6): and the
2 1 1 1 0.45 0.45 rated surge voltage for the equipment;
2.5 2) 1.5 1.5 1.5 0.60 0.60 – for other basic insulation (see 4.3.3.4.2): the highest
3 2 2 2 0.80 0.80 surge voltage that can occur in the circuit.
4.0 2) 3 3 3 1.2 1.2 1.2 for reinforced insulation, see 5.1.6.
5 4 4 4 1.5 1.5 1.5 2) 3) Preferred values specified in 4.2.3.
6.0 2) 5.5 5.5 5.5 2 2 2 For printed wiring material, the values for pollution
8.0 2) 8 8 8 3 3 3 degree 1 apply except that the value must not be less
than 0.04mm, as specified in Table F.4.
10 11 11 11 3.5 3.5 3.5 4) The minimum clearances given for pollution degree 2
12 2) 14 14 14 4.5 4.5 4.5 and 3 are based on the reduced withstand characteris-
15 18 18 18 5.5 5.5 5.5 tics of the associated creepage distance under humidity
20 25 25 25 8 8 8 conditions (see IEC 60664-5). 14
25 33 33 33 10 10 10 5) For parts or circuit within equipment subject to surge
30 40 40 40 12.5 12.5 12.5 voltages according to 4.3.3.4.2 interpolation of values
40 60 60 60 17 17 17 is allowed. However, standardization is achieved by
50 75 75 75 22 22 22 using the preferred series of surge voltage values based
on 4.2.3.
60 90 90 90 27 27 27 6)
80 130 130 130 35 35 35 The dimensions for pollution degree 4 are as specified
for pollution degree 3, except that the minimum clear-
100 170 170 170 45 45 45 ance is 1.6mm.