I was reading a high voltage pcb design guide and it talks about insulators insertions, routed slots, gradient rings, etc.. but it doesn't talk about creepage. As the creepage could be achieved by inserting a barrier or even be a hole on the PCB, here is my confussion.

Talking with my pcb manufacturer he also makes difference between creepage and routed slots close to the conductor pads.

routed slot creepage and clearance

He said that hole width must be calculated depending on the required voltage between pads to protect from arching. I know how to calculate distances for clearance and creepage. But if slots must be calculated I don't know how to do it. I didn' t find any information about routed slots like the pict. So, I hope someone here could tell me how to do it.

  • \$\begingroup\$ Your illustration on the right is correct, you need to observe the clearance dimensions in a straight line, and creepage dimensions along the shortest path over the surface, including slots and (well cemented) barriers, so the path goes around the end of the slot. \$\endgroup\$
    – Phil G
    Commented Jun 13, 2019 at 14:06
  • \$\begingroup\$ The red clearance line in the illustration on the right across the slot actually consist of creepage (towards the slot) + clearance (across the slot) + creepage (to the next trace). So, actually it should be a blue-red-blue line. If you only use the red part, so only this 1 mm as distance for clearance, you're safe for sure. \$\endgroup\$
    – Huisman
    Commented Jun 13, 2019 at 14:22
  • 1
    \$\begingroup\$ If you design allows it, make the slot width as big as the clearance distance needed for the high voltage. \$\endgroup\$
    – Huisman
    Commented Jun 13, 2019 at 14:29
  • \$\begingroup\$ Hi @Huisman, thanks for the explanation. I know clearance and creepage concepts. My question is about doing routed slots, as the left pict. According my manufacturer seems to be a different isolation method. How can I calculate width and large dimensions of the slot? So can I use a cleareance calculator as you have said before? \$\endgroup\$
    – Suvi_Eu
    Commented Jun 13, 2019 at 14:30
  • \$\begingroup\$ @PhilG thanks but the manufacturer says that they make projects with slots and creepage. So I understand that they are two different things. But I don't know how to use routed slots, how to calculate its hole width. I can not use any barrier under my component (reed relay), where the coil pads are. I will like to route a slot. But I don't know how to route it (a hole similar to the left pict). \$\endgroup\$
    – Suvi_Eu
    Commented Jun 13, 2019 at 14:33

1 Answer 1


Let red be the slot width and purple be the slot length, then

  • have the width be determined by the required clearance corresponding to the applied high voltage.
  • have the length and shape of the slot be determined by the required creepage corresponding to the applied high voltage.

Choosing the width equal to the required clearance distance assumes the high voltages are on both edges of the slot. In your case, there is first a creepage towards the edge of the slot, the there is the clearance across the slot, then another creepage towards the other trace, making it actually extra safe/over-dimensioned.

The blue line determines the real creepage. I think most modern PCB tools can calculate track length for you, so you can draw a line or a track like i drew the blue line and add up their lengths. Draw several blue lines to find out which is shortest and check whether the shortest blue line still satisfies the required creepage distance.

enter image description here


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