There are many reasons you might want to cut a plastic electrical plate. For example, you might need to cut it in half for a custom application, or you may want to drill a bigger hole to allow you to run cable wires through it. There are two basic adjustments you might need to make to your wall plate: line cuts and circles.
Remove the cover plate from the electrical outlet. Most cover plates have one or two screws. A screwdriver works best for removing the cover. Never attempt to cut a cover while it's installed. You could shock or electrocute yourself.
Place a piece of painter's tape over the face of the cover plate. This protects the plate from surface scratches.
Draw a line to follow on the backside of the cover plate, using a marker. This is the line you need to follow when cutting.
Place the cover face down on the table of a scroll saw, turn the saw on and slowly slide the cover plate past the blade while keeping the blade on the line. A scroll saw has a very thin blade that will not crack the plastic. The blade also allows you to cut curves, if needed.
Cut a Circle
Place the cover plate on a flat wooden surface on its face. Use a piece of scrap wood under the plate so you don't damage your work surface.
Place a clamp on each end of the cover plate — not over the plate, but butted up against the ends of the plate. This will prevent the plate from spinning when you try to drill it.
Secure a hole saw bit to your hand drill. Place the drill on the slowest speed setting.
Place the blade against the cover plate and hold it at a 90-degree angle to the cover plate.
Turn on the drill and apply slight downward pressure. Allow the teeth to cut into the plastic. Plastic wall plates are usually made of phenolic resin, or Bakelite, which is fire-resistant, but brittle. Pushing too hard on the tool or flexing from side to side risks cracking the plate. Do not stop drilling until you go through the other side of the plate.