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If the hot AC trace of 240-264 V has a 10 mil (0.254 mm) of clearance to the polygon and 35 mil (0.889 mm) clearance to the pad, will this cause it to arc and current to flow? Or even if these clearances are small there still enough clearance to prevent from arcing and shorting the pad?

enter image description here

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  • \$\begingroup\$ Impossible to say without knowing what the polygon and pad are connected to. \$\endgroup\$ Commented Aug 27, 2023 at 8:31
  • \$\begingroup\$ Hi Tim, yes, the clearances should increase. The polygon is neutral and the pad is connected to a 47k resistor to earth. I was reading this article found on an Altium page as a link for more information smps.us/pcbtracespacing.html. For so-called functional insulation, UL 60950-1. \$\endgroup\$
    – Citi
    Commented Aug 27, 2023 at 8:58
  • \$\begingroup\$ but this so-called functional insulation UL 60950-1 described in the article is only for secondary circuits. thank you. \$\endgroup\$
    – Citi
    Commented Aug 27, 2023 at 9:08
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    \$\begingroup\$ The creepage and clearance distances are meaningless without a pollution degree spec. So you need to specify it as well. Because, for example, in a dusty environment the risk of a short or arc can become higher than in a cleaner environment. If there's a fan constantly blowing air the risk can become even higher. PS: The distance requirements differ by the layer that the tracks and the pads are placed on. For a through-hole pad, this may become meaningless but still a good thing to keep in mind. \$\endgroup\$ Commented Aug 27, 2023 at 9:35
  • \$\begingroup\$ FUNCTIONAL type insulation applies to primary-primary connections as well; see §1.2.9, 5.3.4, and Annex G. \$\endgroup\$ Commented Aug 27, 2023 at 9:54

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For example the IEC 61010-1:2010 say the value for clearance depends on :

  • the type of insulation (basic insulation, reinforced insulation, etc.);
  • the pollution degree of the micro-environment of the clearance .
  • altitude with multiply coefficient for heights above 2000m
  • measurement category CAT II, CAT III etc...

Assume a printed circuit board CAT II, an installation at altitudes below 2000m, basic insulation (class I device) with a primary main circuit between 150VAC RMS and 300VAC RMS and pollution degree 2 as the TTI QL355 power supply for example.

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Table 4 of the standard stipulates : 1.5mm clearance and 1.5mm creepage.

ps : For reinforced insulation, the clearance distance shall be twice the value specified for basic insulation. The pollution degree can depend IP indice enclosure.

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IEC 60950 has details on creepage distance from a safety perspective, but I always assume at least 2.5mm clearance is required. For HV-LV separation, a routed slot in the PCB is also a sensible precaution.

0.254mm is not going to be enough for 240V!

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