Switch – Wiring a light switch that only has one cable when the new switch (with neon indicator) has live and neutral both in and out

If the switch you are replacing is in an electrical box that is grounded there is a possibility that insulation in one if the hot wires is compromised and shorted to the box. This would create a direct short when the wire becomes energized and cause the breaker to trip.

The other possibility is that this switch controls an electrical outlet in addition to a light. Switched outlets are common in living rooms and some bedrooms. In bedrooms with a switched outlet a ceiling light may have been added after the original installation so that the switch controls both. In your case you may have replaced the switched outlet and wired it incorrectly. The error may not have become obvious until you came to work on and replace the switch.

Assuming that all 4 switches go directly to 4 different lights. Each light has to have a hot switch leg and a nuetral. In the switch box there has to be a branch circuit consisting of a hot wire (if Romex, the black wire) and a nuetral wire (if Romex, the white wire). All the light fixtures will have two wires comming into the switch box. Hook all the whites together along with the feed nuetral from the branch circuit. Hook one side of each light switch screw to to the branch circuit Hot wire. Hook the other side of the each light switch screw to the wire that goes to one of the four light fixtures. Looking at your smart switch it looks like it needs a nuetral hooked to the white wire and the two blacks are for the hot wire from the branch circuit and the other black is a switch leg that goes to which ever light fixture you are trying to control with the smart switch.