Q: I’ve seen electricians cram an amazing number of wires and switches into wall boxes—especially for gangs of three or four switches. What are the guidelines for determining box size, and how can you prevent overcrowding in a box?

A: David Herres, a licensed electrician in Clarksville, N.H., responds: When a box is overfilled to a point where excessive force is needed to push the devices (switches or receptacles) into place, you’re asking for trouble. Wires can loosen or spring free of wire nuts, causing the circuit to fail, or the insulation on the wires may become...

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