Will a cut or a slot in a PCB change clearance or creepage?

Question

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?

Answer 1

You are correct:

Here is a nice picture of the definitions of 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.

Answer 2

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.