How to get new wire into old box in plaster wall?

by zwiebelspaetzle   Last Updated June 30, 2020 02:21 AM - source

I'm rewiring my house, which was built in 1921. I need to bring new cable to a triple-wide switch box (see photos). I cannot push the old knob & tube wire out through the knockouts--it must be stapled near the box. There is an unused knockout, but I haven't been able to knock it out from within the box. I removed the mounting screws, but it is set firmly in the plaster, so I can't just slide the box out.

inside top of box Note the screws coming in from the top. Perhaps another metal plate above holds there together.

triple-wide box

Is there a trick to pushing the old cables out, or removing the knockout from inside the box? Maybe drill a hole in the knockout and then pull it inward? Is there any way less destructive than cutting all around the box to remove it?

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