Electricity + Control April 2019

ELECTRICAL PROTECTION + SAFETY

ments shall be made between the assembly man- ufacturer and the user. The user must inform the manufacturer if such special service conditions exist. Special service conditions include, for exam- ple: 1.2.1 Values of temperatures, relative humidity and/or altitude differing from those specified in the standard. 1.2.2 Applications where variations in temper- ature and/or air pressure take place at such a speed that exceptional condensa- tion is liable to occur inside the assembly. 1.2.3 Heavy pollution of the air by dust, smoke, corrosive or radioactive particles, vapours or salt. 1.2.4 Exposure to strong electric or magnetic fields. 1.2.5 Exposure to extreme climatic conditions. 1.2.6 Attack by fungus or small creatures. 1.2.7 Installation in locations where explosion or fire risks exist. 1.2.8 Exposure to heavy vibration, shocks or seismic occurrences. 1.2.9 Installation in such a manner that the current-carrying capacity or breaking capacity is affected, for example, in equipment built into machines or re- cessed into walls. 1.2.10 Exposure to conducted and radiated dis- turbances other than electromagnetic, as covered in the standard. 1.2.11 Exceptional overvoltage or voltage fluctu- ations. 1.2.12 Excessive harmonics in the supply voltage or load current..

a reduction of the dielectric strength or surface resistivity of insulation. There are different degrees of pollution which refer to the environmental conditions for which the assembly is intended. For switching devices and components inside the enclosure the pollu- tion degree of the environmental conditions in the enclosure is applicable. So, for the purpose of evaluating clearances and creepage distance the four (4) degrees of pollution in the micro-en- vironment, as outlined below, are established. Themicro-environment (of a clearance or creep- age distance) entails the immediate environment of the insulation which particularly influences the dimensioning of the creepage distances. It is important to note that the micro-envi- ronment of the creepage distance or clearance and not the environment of the assembly it- self, or of the components, determines the ef- fect on the insulation. The micro-environment may be better or worse than the environment of the assembly or components. 2.1.1 Pollution degree 1 No pollution or only dry, non-conductive pollution occurs. The pollution has no influence. 2.1.2 Pollution degree 2 Only non-conductive pollution occurs, except that occasionally a temporary conductivity caused by condensation is to be expected. 2.1.3 Pollution degree 3 Conductive pollution occurs or dry, non-conductive pollution occurs, which is expected to become conductive due to condensation. 2.1.4 Pollution degree 4 Continuous conductivity occurs due to conductive dust, rain or other wet conditions. Pollution degree 4 is not applicable for a micro-environment inside the assembly manufactured to this standard. 2.2 Therefore, unless stated otherwise, assem- blies for industrial applications are generally for use in a pollution degree 3 environment. However, other pollution degrees may be con- sidered to apply, depending upon particular ap- plications or the micro-environment itself.

Special service conditions may include: variations on temperature, exposure to other extremes outside the normal service conditions. humidity or altitude, or

1.3 Transport, storage and installation conditions

A special agreement shall be made between the assembly manufacturer and the user if the condi- tions during transport, storage and installation, for example, temperature and humidity conditions, differ from those in the standard.

2. Pollution / pollution degree

2.1 Pollution is essentially any addition of solid, liq- uid or gaseous foreign matter that can result in

Electricity + Control

APRIL 2019

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