DSH 657 Characterizing the pollution degree of micro-environment within a sealed

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DSH 657

Characterizing the pollution degree of micro-environment within a sealed device that has switching c ... 8 v/ ]. c" K9 J8 z# u& _- f

20.2.2   f* y3 m4 K0 f1 a6 A. |

60730-1(ed.3);am1;am2 8 e* G& ?. x9 H2 d

" N" q" m  C6 k- gQuestion:
Clause 20.2.2 of IEC 60730-1 states that creepage distances for operational insulation shall be as specified in table 20.4 based on the material group and the pollution degree. What is the pollution degree of the micro-environment within a sealed control that has switching contacts?
  C5 p1 j& j, |# E( YExample: Bimetal temperature sensing device. IEC 60730-2-9 does not give any additional guidance. Even though the micro-environment is sealed (by construction) from influence by the external environment, the pollution situation can be conductively contaminated due to ionization of the contact material and out-gassing of the plastic parts that may be near the switching
mechanism. This is very similar to sealed relays covered under IEC 61810-1. In this standard, creepage distances inside a relay are specified in accordance with pollution degree 2.
2 f- z. e& d4 o0 o3 ^( m2 X8 ?Decision:
For controls, an endurance test and a high voltage test in combination are required. If sealed contacts of a control have passed the endurance test and the high voltage test, it could be assumed that the pollution and the ionized gases in the sealed control does not influence the creepage and clearances of the control. Therefore pollution degree 2 in accordance to Annex N (normative) of IEC 60730-1 could be defined.
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