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Does a cut or a slot in a printed circuit board increase clearance, creepage or both?

Some say it will increase clearance, but I don't think clearance will change because, even with a cut in the PCB, distance over the air will be the same. Thus, a cut will only affect the creepage distance. Please correct me if I'm wrong.

Or does it have nothing to do with either clearance or creepage, and is only for isolation?

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    \$\begingroup\$ stackexchange doesn't work like your average bb forum, if you have a follow up question, you ask a new question, you don't edit your existing one to ask more. \$\endgroup\$ – PlasmaHH May 18 '16 at 8:55
  • \$\begingroup\$ Ok, I asked this on new question. \$\endgroup\$ – Bharav May 18 '16 at 9:22
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You are correct:

Here is a nice picture of the definitions of creepage and clearance:

Creepage and clearance

Note that adding a barrier will increase the clearance. Adding a barrier increases the physical length of insulated material between conductors, and that is what is considered when defining clearance. Normally a barrier is inserted into a slot (or slots) in the PCB.

Creepage and clearance are of great importance for high voltage isolation.

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Slots will only increase creepage. You need a barrier if you need to increase clerance.

Also, remember to make the slot >2 mm wide, otherwise it does not count by most standards.

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  • \$\begingroup\$ Usually > 1mm is sufficient, eg blog.optimumdesign.com/… \$\endgroup\$ – Martin May 18 '16 at 7:58
  • \$\begingroup\$ Ah! Didn't know that. We always use 2 mm to be on the safe side for world-wide sales and approval of far-away saftey agencies which may or may not have slightly different ideas how to interpret the rules. \$\endgroup\$ – winny May 18 '16 at 8:55

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