circuit breaker trips on a line containing fan and light

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  #1  
Old 11-06-13, 09:24 PM
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Question circuit breaker trips on a line containing fan and light

Originally I had to replace a light switch in a box that also contained the switch for the fan. After repair everything worked normally, then one day I turned one of the switches on(I don't remember which one) and the circuit breaker tripped. Playing with it a little, I noticed that it didn't matter if the switches were off or on, it still tripped. I took the wires off both switches and tried the circuit breaker again. It stayed connected. There are two wires coming into the box that the top of the switches connect to. a green one and a red one I believe, although I cant recall for sure now. A black wire connected both switches at the bottom. While the CB was connected I Checked the voltage across each wire to ground. The light switch wire red 122 volts, which was in the ball park but the voltage across the fan wire only read 97 volts. Is this normal for the fan? Is it because maybe the fan is set on one of three speeds and is not turned off at the fan? My career was in Aviation Electronics not residential wiring, so I'm not sure what the light/fan situation is or how it is wired. At present, I just disconnected the fan completely, and use just the light but I would like to get it corrected.
Thanks,
Annis
 
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Old 11-06-13, 11:01 PM
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Welcome to the forums!

While the CB was connected I Checked the voltage across each wire to ground. The light switch wire red 122 volts, which was in the ball park but the voltage across the fan wire only read 97 volts. Is this normal for the fan? Is it because maybe the fan is set on one of three speeds and is not turned off at the fan?
It sounds like you were testing with the switches. wired in. Tests for voltage must be done on disconnected wires. But voltage isn't your problem anyway. The problem you're describing is a dead short.

Kill the power, open the switch box and pull the switches out far enough to be able to see everything. Is the box metal? Is it grounded? Do you see any place where it looks like an arc burned something?
 
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Old 11-07-13, 04:48 PM
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No I tested with the switches wire in but off. Across the light switch I read 120 volts but across the fan switch only 97 volts. Composite(plastic box) Nothing burned.
 
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Old 11-07-13, 04:58 PM
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Yes.....the voltage when checking across the switch's terminals is load dependent when the switch is off(or open). Multiple fans speeds will yield different voltage readings.

If the circuit tripped when the switches were on or off and there are no shorts there...... then the problem sounds like it's not at that switchbox.

I'd start checking other things or boxes on the same circuit.
 
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Old 11-07-13, 06:22 PM
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I tested with the switches wire in but off. Across the light switch I read 120 volts
If you remove the bulbs you'll read 0 volts. You are reading the voltage through the bulbs.
 
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Old 11-07-13, 08:39 PM
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Ok I checked the fan/light combo in another room. This one reads 120 volts across both light and fan with switches open of course. For some reason, in the problem circuit, this light/fan system is the only thing on the breaker, so by deduction, one of the fan speeds must be shorted or nearly so.
 
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Old 11-08-13, 09:18 PM
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UPDATE: Pencil and paper sometimes works better than a voltmeter! After drawing out the fan circuit with a 3 position switch at the fan and a simple toggle switch at the switch box. I see that i am probably reading the 97 volts through a lower speed winding or tap. This could mean the fan is OK after all or it could mean that it's still shorted to ground somewhere. As the original fan toggle switch was destroyed trying to remove the wires i will install another and see if the CB trips again. This should tell me what I need to know. Does anyone differ or care to comment? I am often wrong so my feelings won't be hurt!
 
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Old 11-08-13, 09:34 PM
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You said:
"in the problem circuit, this light/fan system is the only thing on the breaker"

It is unusual to have only a paddle fan on a separate breaker. I would be looking for other dead fixtures.

One thing that you can do which will save a lot of aggravation in the future is to map out all the circuits in your house. That way, if breaker #17 goes off, you can look at your map an see where every fixture / outlet on #17 is located.
 
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Old 11-09-13, 05:42 PM
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It is unusual to have only a paddle fan on a separate breaker. I would be looking for other dead fixtures.
This whole house is unusual! I have been frustrated with this house ever since we bought it. It was only 5 years old when we bought it 10 years ago and so is relatively modern. The builder(we found out later) used shoddy materials, took short cuts just about everywhere. Although from what I can see the wiring is mostly to code, I strongly suspect his construction workers wired the houses and not a licensed electrician. I recently replaced a ceiling fixture upstairs and found the box was not even secured to a joice! The fixture itself was cheap and had started arcing which was the reason I replaced it.

No I have went through the house and there are no other lights or outlets connected to the breaker. There are surplus breakers in the box however. Which probably means some others are overloaded.
 
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Old 11-09-13, 11:53 PM
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I'm completely lost here. If you turn the switches off...... which means they are open.... how can the fan be the problem since it's not connected to power ??
 
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Old 11-10-13, 11:17 AM
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PjMax: Well the CB was tripping whether the fan or lights were on or not. I went in and disconnected the switches( both wires off each switch) I could then close the CB without it tripping I reattached the Light and the CB stayed connected(did not trip) Unfortunately The fan switch broke when I was removing it so i didn't try checking it with the wires on and the wires off the light switch. I think where the confusion came in was when I checked the voltage across the wires that led to the fan switch and got a lower voltage than I was expecting. I didn't realize the voltage at that point would depend on where the fan speed switch was set. After I drew a diagram on paper, I saw my mistake.

Since the Fan/Light combo is the only thing on that circuit(Odd, I know) By the process of deduction, the only thing left is the fan.
Anyway it's gonna be solved(I think) in a few minutes because I'm going to wire in another switch.
 
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Old 11-10-13, 07:06 PM
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Anyway it's gonna be solved(I think) in a few minutes because I'm going to wire in another switch.
Or you could use a wire nut to temporarily connect the two wires the switch would connect.
 
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Old 11-11-13, 07:24 PM
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Or you could use a wire nut to temporarily connect the two wires the switch would connect.
Didn't think about that! Well I put a new switch in the fan circuit and everything worked. I tried all three speeds, thinking maybe one was shorted, but they all worked. Now I'm confused! The switch is wired in the "hot" wire, but it is in a plastic box, the returns are all connected together in the box by an insulating wirenut. Just how could the switch get shorted so that it tripped the CB?
 
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Old 11-11-13, 08:32 PM
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Originally Posted by Nashkat1
Or you could use a wire nut to temporarily connect the two wires the switch would connect.
Didn't think about that!


I put a new switch in the fan circuit and everything worked. I tried all three speeds, thinking maybe one was shorted, but they all worked.
Great. Glad you got it resolved.

BTW, if the switch you installed to control the fan motor is an on/off switch, I strongly advise you to replace it with a fan motor control. Supplying power to a fan motor - or any induction motor - when it has built-in controls that limit the power it receives is hard on the motor, or can be. If the built-in speed control is set at "full" or "high" there shouldn't be a problem. But if it's set at "low" or medium" the motor will be strained as it tries to start, and is likely to be damaged as a result

Now I'm confused! The switch is wired in the "hot" wire, but it is in a plastic box, the returns are all connected together in the box by an insulating wire nut. Just how could the switch get shorted so that it tripped the CB?
Hmmmm... Maybe the grounding conductor somehow got close enough to one of the switch terminals to create a short?
 
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Old 11-11-13, 09:00 PM
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Well the set up is standard, I think, At least for this SD. There are fans in each bedroom witha light fixture below the fan. Even though the fan and light have separate pull switches there is a regular 2 switch on the wall, one for the fan and another for the light. It is this set of switches where the problem was. This is kind of a long story, hope you don't mind. I had originally changed the light switch at the wall because it WAS bad. In replacing the switch i goofed. The wire going to to the bottom of the light switch was simply looped around the screw then continued to the bottom of the fan switch. Not realizing this, I cut it off. Now I knew that I had goofed and the only way to correct it was to take the original wire from the bottom and twist it together with two others with a wirenut. having one wire each to go to the bottom of the switches. Since their wasn't much room in the box I went to Lowes and got a three wire connector that I could push the wires into and they were all connected. Put it together and it worked fine..for a couple of months. That's when it tripped the breaker one day when I went to turn it on. When I just replaced the switch I got a new connector and redid the whole thing. I'll let y'all know if it dies again in a couple of months!

Thanks for all your help!
Annis
 
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