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Recently I found a resistor broken on a PCB. It is a MOF type 1/2W through hole resistor. I found that the resistor is directly placing (touching) on a PCB Live trace and I know that the potential difference between the resistor and the trace is about 220Vac. There is a small hole on the resistor and a burning mark on the PCB trace. Therefore I presume an electric arc was formed between the resistor and the PCB.

Then I read the safety standard EN60335-1. For the part describing creepage and clearance, it has a remark: "Lacquered conductors of windings are considered to be bare conductors" As I know common MOF resistor body is just a lacquered coating,

I would like to ask is this resistor considered as "Lacquered conductors of windings"? If so this is violate the safety standard.

If this is not, is a MOF through-hole resistor body touching a Live PCB trace violate the standard?

Appreciate if you can provide strong supporting document or information.

Thank you very much

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  • \$\begingroup\$ Considering something to be a bare conductor violates no standards. It’s how you implement it that is important. \$\endgroup\$ – Andy aka Feb 6 '18 at 16:49
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    \$\begingroup\$ The way you describe it would depend on the dielectric strength of the resistor's insulation. It seems like a bad design to put it on top of a high voltage trace. \$\endgroup\$ – EE_socal Feb 6 '18 at 18:11
  • \$\begingroup\$ @Andy aka However in the situation I described, if the resistor is considered as a bare conductor, and it is touching the PCB trace (with solder mask), I am sure that it violates the standard. \$\endgroup\$ – eepty Feb 6 '18 at 18:42
  • \$\begingroup\$ @EE_socal Yes, but it is rather difficult to get the information of the dielectric, because this PCB is not my design. Actually I also think this is a bad design, but I want some solid supporting document to support me. \$\endgroup\$ – eepty Feb 6 '18 at 18:45
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    \$\begingroup\$ It’s the designer that violates the standard in my book. After all, resistors and copper tracks can’t read. \$\endgroup\$ – Andy aka Feb 6 '18 at 19:11

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