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Kevin, Licensed Electrical Contractor
Category: Electrical
Satisfied Customers: 3600
Experience:  30 years Licensed Electrical Contractor in Illinois, Adjunct College Electrical Instructor, Former Electrical Inspector, Diploma: Digital Electronics, FCC Technician License
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I have a three gang switch in our master bath. A few nights

Customer Question

I have a three gang switch in our master bath. A few nights back my wife walked in in the middle of the night and turned on a light to walk to the toilet. She initially turned on the first switch, which controls a four light fixture over our sinks. She decided this was too much light and turned it off and then switched on the second switch, which controls the light over our tub. She heard a loud pop and the light did not come on. Since then, none of the lights in the gang will operate. We checked the breaker and it is fine. Other lights on that circuit breaker operate, such as our walk-in closets. I just disconnected each of the switches in sequence and did a continuity test on each switch, starting with the third switch (which was not used in this incident) and proceeding to the second (the one switched before the pop) and then the first which came on as described above. I first tested continuity on the meter itself, I then tested each switch (totally disconnected) and each showed resistance when switched on and registered 1 when switched off. I then tested one bulb from each fixture just to make sure that they all didn't blow. They all worked. What am I missing?
Submitted: 10 months ago.
Category: Electrical
Expert:  Kevin replied 10 months ago.

Hello and welcome to Just Answer. My name is ***** ***** I will be happy to assist you with your electrical question.

1) A popping noise indicates that arcing took place due to a short circuit. Most likely a faulty termination or a loose wire splice.

2) Depending upon where the circuit originates at the switch box or at one of the light fixtures or an exhaust fan, I would suspect either a loose wire termination or a faulty wire nut splice or a bare copper ground wire came into immediate contact possibly with a side terminal screw on one of the wall switches.

3) If the switches were back-stab wired, this is a common problem where the wire can easily come loose and cause a direct short. On any devices, wires should only be terminated to the side screws and never the back-stab insert holes.

4) You will need to perform a visual inspection at each of the switches. A multi-meter to confirm voltage measurements is also required in order to troubleshoot and locate the problem.

Customer: replied 10 months ago.
I'm adding photos of the switch disassembled, the lights in question, and the multimeter I'm using.1) That makes sense.
2) I suspect at the switch, but I can look at the two ceiling lights from the attic to tell for sure. While I'm there, I can also inspect the area around light in fullsizerender3, to see if there's any indication of a faulty wire, etc. since this is the direction my wife heard the pop from and that was the light she was turning on.
3) Only one switch had a back stab and it was not the one being used in this case. I think the back stab runs to the fan integrated into the light in fullsizerender, because both the fan and the light are controlled from the same switch. The other two lights are all terminated with the side screws.
4) I've looked at each switch and tested them while completely disconnected with the multimeter as shown in the photo. All showed some reading other than 1, when the switch was moved to the on position. If there is another test you want me to do please let me know, but I will need to leave for a meeting in about 30 minutes.I put each switch back exactly as I found it immediately after testing it so I wouldn't mix anything up.
Expert:  Kevin replied 10 months ago.

Thanks for the replies and the pic's.

1) I am not able to make a phone call at this time.

2) Can you measure a constant 120 volts on one of the switch brass screws to neutral or to ground whether the 3 switches are ON or OFF?

Customer: replied 10 months ago.
I will attach a video I did testing 2). Please let me know if I did this incorrectly. I didn't see any current. Prior to the video I tested it in an outlet to ensure it worked and I was using it correctly. It showed 120. I also verified the circuit was working by turning on the light in my walk-in closet. Unfortunately, I will be gone most of tomorrow.
Customer: replied 10 months ago.
It won't let me upload this video, even though it's under the limit. I've tried three times. "It says an unknown error occurred. Please try again." I set my meter to 200 ACV and touched the ground/neutral, ground/hot, and hot/neutral. Nothing showed any current. I did this with the switch in both the on and off position, if that matters. If I did this wrong, let me know how I need to do this different.
Expert:  Kevin replied 10 months ago.

Thanks for the replies.

1) If none of the switches measure a constant 120 volts, then that means there is a loose hot wire termination or a faulty splice upstream of the switches. It is possible that power originates from one of the lights and the hot issue could reside in one of the light fixture boxes.

Expert:  Kevin replied 10 months ago.

If you have any additional questions, just let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.