@NickAlexeev they're two different distances basically

the endpoints are the same, the paths are different though

@NickAlexeev Hard to visualize exactly what you're talking about. Creepage distance needs to go around any air gap, but clearance goes right over an air gap. So clearance in your conditions requires 2.5mm direct line between nearest conductors. If you put a slot in the middle, you can make the creepage meet your requirement too.

I don't know about the size of the slot you require, but you'll measure Point A, line to top (or bottom) of slot, line to point B.

@NickAlexeev I'm pretty sure the width of the slot will be dependent on voltage -- at least for high voltage.

@ScottSeidman In my situation, it’s not a slot in a board or a distance between traces on one board.

I’ve got a board which has to go into a metal** enclosure. The enclosure is earthed, and the entire PCB is patient side. The required clearance and creepage are 2.5mm and 4.0mm.

If the PCB touched the enclosure, then the PCB should have a 4.0mm creepage distance to the nearest copper on the PCB. If the edge of the PCB were 2.5mm away from the enclosure, that would be the clearance. What about the case when there’s 50% clearance and 50% creepage?

The are options for increasing the clearance (shrinking the PCB, enlarging the enclosure). But I wonder if clearance and creepage are additive. As a separate theoretical question. Or, as a 60601 “letter of the law” question.

@NickAlexeev Everything I can find suggest your creepage with respect to the chassis is infinite, at least with respect to the air gap. Now, if you're using nylon standoffs, or something, that will certainly impact your creepage. I'm no expert, of course.