I am not familiar with IEC 1010, but have a copy of 664-1. It is allowed for Functional Insulation to interpolate creepage distance values for intermediate working voltages. However, Table 4 has an entry for 250 V rms, and for Pollution Degree 2 on a printed wiring board (not Material group IIIb) the minimum creepage distance is 1.0 mm.
If Basic Insulation is required you are supposed to use the rationalized Voltage through Tables 3a/b, based on the rated voltage of the equipment. If your nominal supply voltage of your single phase supply system is between up to 240 V, the 'rationalized' voltage is 250 V. This leads to the same Creepage Distance as for the Functional Insualation. For your information, IEC 950 has information on minimum saparation distances for coated printed circuit boards.(Subclause 2.9.5, Table 7) Here for a working voltage of up to 250 V rms the minimum distance for Functional/Basic or Supplementary Insulation is 0.6 mm. However, there are some requirements on the coating process of the boards. > >As an electronic designer for laboratory devices, our designs have to >comply with the IEC 1010 safety standard. >At this moment I have a few questions about this topic. > >- Routine tests > For EMC purposes we use 275 V varistors between fase-earth and > neutral-fase. According to annex K.2 of amendement 2, a test voltage > of about 2000 Vdc must be applied between the mains terminals > connected together (fase and neutral) on one side, and all > accessible conductive parts (earth) connected together on the other. > No breakdown or repeated flashover shall occur. It's clear that > breakdown will occur. > In annex K.3 it's noticed that if voltage limiting devices are used, > the applied voltage may be less. But this exeption does apply for > the mains test of annex K.2 to my opinion. Is this correct? > >- Interpolation of CREEPAGE DISTANCE > Annex D.3 of IEC 1010 states that interpolation of CREEPAGE DISTANCE > is permissible in accordance with IEC 664 table IV. > As I'm not in the possession of this standard, I would like to know > if this is a liniar interpolation. I will give an example. > The working voltage is 240 Vac, basic insulation is required, > pollution degree 2, and installation (overvoltage) category II. The > CREEPAGE DISTANCE is determined in Table D.4. > > Working voltage CREEPAGE distance on printed wiring board > 150V 0.5 > 300V 1.5 > > Distance = (Working voltage / 150) - 0.5 > For 240 V the CREEPAGE DISTANCE will be 1.1 mm. Is this correct? Mit freundlichen Gruessen/Best regards, V. Gasse INTERNET: [email protected]
