Can you put two wires on a Square D breaker?

Generally, you cannot put two wires on a single Square D breaker unless that specific breaker is explicitly designed and listed for two wires, which most standard Square D breakers are not. The National Electrical Code prohibits double tapping, which is connecting two conductors to a breaker terminal that is rated for only one conductor, because it can cause loose connections, overheating, and fire. Most Square D Homeline and QO single-pole and double-pole breakers have a terminal rated for only one wire. If you put two wires under one screw, one or both may become loose over time due to different expansion rates and improper torque, leading to arcing. There are a few exceptions. Some Square D breakers, particularly certain QO and Homeline breakers rated 10 to 30 amps, are designed with a special pressure plate that allows two wires of the same gauge and material, and the breaker will be clearly marked on its side or label as suitable for two wires. These are sometimes called double wire or two-wire rated breakers. If your breaker is not marked for two wires, you must not double tap. Instead, you should add a tandem breaker if the panel allows, install a subpanel, or splice the two wires together with a pigtail wire nut and connect a single pigtail to the breaker. Always follow the panel labeling and torque specifications.