How much distance I have to create on a PCB between a coated conductor and an uncoated component pin with a voltage difference of 200V? From different websites and calculators I can only get the information how much distance is needed between two coated conductors or two uncoated pins, but not a mixture of both.

  • \$\begingroup\$ Is there enough room to use the largest distance? \$\endgroup\$ – Andrew Morton May 16 '18 at 8:55
  • \$\begingroup\$ Unfortunately not. That would also have been my approach if there would be enough space. \$\endgroup\$ – electricar May 16 '18 at 9:05

In cases such as this you should probably plan for worst case, which is two uncoated conductors. According to IPC-2221B, with a 200V supply (assuming 200V peak, as in 200V DC or 200V pk AC) you must have a clearance between two uncoated conductors of at least 1.25 millimeters. This is the number I would use for the design, even though you theoretically could get by with a little bit less. This just provides a bit of safety margin, which is especially important because you don't know where the line is between coated and uncoated.

If you don't have enough room for this sort of clearance, I would suggest rearranging your board. I wouldn't trust a clearance of any less, and you really need to make it work, no matter what. Consider running high voltage traces on an internal layer or on the underside.

  • \$\begingroup\$ Making slots in the PCB to break the creepage is a valid solution as well. You see that quite a lot actually on CAT IV devices etc. \$\endgroup\$ – Barleyman May 16 '18 at 10:58
  • \$\begingroup\$ @Barleyman Sure, and I use slots on all of my high-voltage boards, but if you don't have room for a 1.25 mm space between tracks you probably don't have room for a slot. Most manufacturers want at least 3 mm slot diameters \$\endgroup\$ – DerStrom8 May 16 '18 at 11:05
  • \$\begingroup\$ I'm pretty sure I have smaller slots. In fact checking the nearest PCB, it's got 1mm slots on it, the fab was ok with these on 2.5mm thick board as well. If I had to pull a figure I'd say I have used a 0.8mm slot with small-ish component(s) like optoisolators. But I don't have that layout to check. The 1mm slots are to suppress "singing capacitors" so the board has quite a few of these. Six SMPS circuits, 5 large ceramics each, 4 slots per capacitor.. 120 slots all told. \$\endgroup\$ – Barleyman May 16 '18 at 12:06
  • \$\begingroup\$ @Barleyman Fair enough, I concede =) \$\endgroup\$ – DerStrom8 May 16 '18 at 12:36
  • 1
    \$\begingroup\$ It obviously entirely depends on the supplier. Anyways, this kind of springboard design is darn sight cheaper than "anti vibration" capacitor mounted on a metal bracket. Also my count was a bit off, some of the capacitors share a slot.. photos.app.goo.gl/H1GojobS6K3LvzUw2 \$\endgroup\$ – Barleyman May 18 '18 at 15:40

This is a complex issue that cannot be answered without particulars of the application. At the cleanest environment with the best materials, you'd look at 0.45mm creepage distance. At the worst environment with no coating this goes up to 3.2mm creepage.

Airgap clearance is a fair bit smaller at this voltage, from 0.2mm to 0.8mm depending again on the environment.

The clearances and creepages are defined in e.g. EN 60950 and EN 62368 standards.

Connectors usually define a max working voltage, that's what you can safely use. Higher voltages might be OK but you have to evaluate the case yourself and get it tested before bringing to market. In other words, if you use higher voltage than the manufacturer specifies, you're responsible for it.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.