The tables in IPC are to isolate different voltages, and if you violate them by using a smaller gap, current can travel across the surface of the board to where you don't want it to be. That's why the recommended gaps for internal layers are so much smaller, no surface to travel across (I think! Someone correct me if I'm wrong). But when you cut a slit the only path is across air, which is MUCH harder to cross, so you can have a much smaller gap of pure air and get the same isolation as a large gap of fiberglass. BUT WARNING! If you go get the figures for air, you have to take into account the altitude and maximum humidity of the environment, because not all air has the same electrical properties! (almost got burned designing power supplies for submarines once) Good Luck, Jack -----Original Message----- From: Çeyiz Tekcan (ARGE - VESTMAN) [mailto:[log in to unmask]] Sent: Tuesday, April 04, 2000 4:00 AM Subject: about using slits for voltage isolation Dear all, I want to know that, how I can use slit to conductor isolation for high Voltages. I know the formula about conductor clearance (from IPC-D-330), if I use slits, would these clearances be decrease? How can we formulate the relationship between slits and electrical conductor clearances ? Thanks in advance Ceyiz Tekcan VESTEL R&D PCB Design Engineer E-mail:[log in to unmask] Phone:+90 236 233 01 31 Ext:2111 Fax:+90 236 233 38 68