Per NEC (National Electrical Code) standards, you can use no more than one wire per screw. Never connect more than one wire under a single screw terminal as it could cause arching wires or a loose hot wire as the wires heat and cool. This will eventually start a fire and other safety hazards.
How do you wire a GFCI with more than 4 wires?
If the outlet box has four wires plus a ground, connect the second black wire to the brass terminal marked Load and the second white wire to the silver terminal marked Load. Connect the ground wire to the green ground screw by inserting the wire into the back-wire hole and tighten the terminal screw.
Will an outlet still work if wired backwards?
But heres the catch: If you connect the circuit wires to the wrong terminals on an outlet, the outlet will still work but the polarity will be backward. The white (neutral) wire should be connected to the silver-colored terminal. If these connections are backward, the polarity is wrong.