This can be for one of several reasons. If so check your service panel breakerfuse box.
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Light switch not working after changing. The electrician used the red wire switched for the light at the outlet. 10 reasons why your lights dont work 1. Insert the leads into a working electrical outlet. If the light is not working there may be a loose wire that did not make connection or was left out of a wire connection all together. There is a good possibility that the problem is either a tripped circuit breaker or a problem in the light fixture wiring. Hot coming in hot going out to next device and hot to switch.
Guide to resetting a circuit breaker inspecting the light fixture wiring. That is especially common if you are using an unreliable cfl light bulb. If the light stays off or the meter reads zero move the lead to the other brass terminal. If upon installation of a new switch the short black wire from the switch to the wire nut causes a tug on the wire nut and a loose connection of the incoming hot is formed then none of the other devices downstream will get power either. Make sure your voltage tester is working before you test the switch. Are you trying to figure out why a light bulb appliance or light fixture is not working when you flip the switch.
If the wires were loosely connected electric arcing may have generated enough heat to melt the plastic casing of the. If you have several light switches or light fixtures that are not working then there may be a short in the electrical wiring or most likely a loose connection has developed. Check to see if the lightbulbs in the light fixture have the proper wattage for the light fixture. Not to suggest that youre a dim bulb pun intended but have you made sure the fixture is. A corroded contactor inside the switch could cause the flicker but would also probably cause the switch to feel warm at the touch. Plug or wall switch.
A wire getting loose in a terminal screw or in a wire connector at the switch or light fixture could cause the flicker. Typically the location of the electrical short will need to located after identifying all of the affected devices that are on the circuits that are not functioning. If the wattage is too. If its working test the switch by touching a lead from the voltage tester to the green ground screw and the other lead to a brass terminal. So that is why you are getting 3 voltages at the switch from hot black to ground red to groundand white to ground. By not breaking the tab you are back feeding power to the switch on the red from the black on the outlet.
If you still get no reading its safe to handle the switch. Other reasons may be more complicated like a faulty device or short circuit. If insulation is packed too tightly around the light fixture it may be trapping heat around the light fixture canister. Usually its a simple solution like a burnt out light bulb. Is anything else in the room failing to turn on.