What would cause a light switch to spark when flicked off?

We just had the whole switch replaced and it was fine now it has a blue spark when shut off. you can only see it through a little crack. is this safe?

Answers:
Although this scares a lot of people if they happen to see it, it happens in a lot of switches and is a fairly normal sight when any pair of contact points are opened. When the points are closed, (the switch is ON), the current flows through the points and causes work to be accomplished in whatever appliance is connected in the circuit, (lite bulbs, ceiling fans, exhaust fans, etc.). When the switch is thrown into an off position, the points are pulled apart and the electricity, in an effort to continue to flow tries to reach out to the other point from the hot side of the circuit. When the points get to a certain distance, the electrical flow isn't strong enough to maintain a connection across the air gap and stops. That's what you see. The odds are you don't see this spark when you turn it on, just when it goes off. Not to worry.

Other answers:
Retighten the screws on the sides of the switch or Replace the switch again.
Retighten the screws on the sides of the switch or Replace the switch again.
YOU HAVE AN ELECTRICAL SHORT IN THE SWITCH, YOU MAY WANT TO CHANGE THAT ONE FOR ONE THAT HAS A RESET BUTTON ON IT,JUST MAKE SURE THAT THE WIRES ARE NOT LOOSE(KINDA TWIST THEM WHEN PUTTING IT AROUND THE SCREW) THEN TIGHTEN IT
Two words, "Loose Connection".
1- Turn off the power.
2- Remove switch.
3- If the wire are plugged in to the holes on the back of the switch, take them out of the round hole by depressing the blade in the square hole underneath and pulling the wire out. (takes a very small flat blade screwdriver), or just cut it off flush.
4- Strip the wire enough and use the screws, wrap the wire end clockwise and tighten the screw. (some cheap switches don't even have the screws).
5- Make really sure the connections are tight. They are not supposed to spark. Sparking is hot and dangerous.
All 3 answers are good advice but we have noticed this in many
new switches. A loose connection on the switch or a heavy load
may cause this sparking and is noticeable because the plastic is
very thin. I would say that you notice it when its dark, in morning or in the evening. We have noticed this more on a decora style switch.
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