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  1. #1
    Sinner's Swing! Bullwinkle's Avatar
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    Default Any Electricians on the Links? Need Advice.

    I recently installed a ceiling fan in my son's room. I figured that just turning off the power at the light switch would kill all of the power going to the existing light fixture, but when I measured the power at the fixture, I got 39 volts.

    I turned off the breaker and measured again. This time it was zero volts. Then I had my wife turn on the breaker while I continued measuring and I watched it crawl back up to 39 volts. (I then turned on the light switch and measured it at 110 volts, so everything is okay on that end.)

    I decided to install the fan with the breaker off because 39 volts is a little past my comfort zone for getting zapped, and the fan is working great, but now this 39 volt thing is bothering me.

    Does this mean that when I turn off the switch, I'm still burning 1/3 of the electricity? I don't like that idea much. Electricity is expensive. (Not to mention that our electric plant is coal powered so I'm not doing much good for the air quality around here)
    What's next? Should I replace the switch? It's probably 30 years old.
    What do you think?







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  2. #2
    Eruption Yerfdog's Avatar
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    Quote Originally Posted by Bullwinkle View Post
    I recently installed a ceiling fan in my son's room. I figured that just turning off the power at the light switch would kill all of the power going to the existing light fixture, but when I measured the power at the fixture, I got 39 volts.

    I turned off the breaker and measured again. This time it was zero volts. Then I had my wife turn on the breaker while I continued measuring and I watched it crawl back up to 39 volts. (I then turned on the light switch and measured it at 110 volts, so everything is okay on that end.)

    I decided to install the fan with the breaker off because 39 volts is a little past my comfort zone for getting zapped, and the fan is working great, but now this 39 volt thing is bothering me.

    Does this mean that when I turn off the switch, I'm still burning 1/3 of the electricity? I don't like that idea much. Electricity is expensive. (Not to mention that our electric plant is coal powered so I'm not doing much good for the air quality around here)
    What's next? Should I replace the switch? It's probably 30 years old.
    What do you think?
    Nah, you're good. Everything is as it should be. (It's normal).
    You're not burning electricity, just a portion of the potential is at the fixture, which is normal. Shutting the breaker off to install the fan is the right thing to do. When the switch is off, 1/3 or half of the potential is there, but with no circuit (the switch being open), nothing is burning. It's the same as the breaker being open - there is potential at the breaker, but no circuit = no electricity being wasted.

    You did the right thing, and everything sounds fine.

    (20+ year electrician)
    I swear, it's like I'm playin' cards with my brother's kids or somethin'. You nerve-wrackin' sons-a-bitches.

  3. #3
    Sinner's Swing! Bullwinkle's Avatar
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    Quote Originally Posted by Yerfdog View Post
    Nah, you're good. Everything is as it should be. (It's normal).
    You're not burning electricity, just a portion of the potential is at the fixture, which is normal. Shutting the breaker off to install the fan is the right thing to do. When the switch is off, 1/3 or half of the potential is there, but with no circuit (the switch being open), nothing is burning. It's the same as the breaker being open - there is potential at the breaker, but no circuit = no electricity being wasted.

    You did the right thing, and everything sounds fine.

    (20+ year electrician)
    Thanks Yerf, it's reassuring to hear from an expert. Everything I know, I learned from a Black and Decker book I bought at Lowe's.

    This leads me to another question if you have time:

    What's up with the 39 volts? Can I still get zapped? I guess I don't understand this "potential" part.

    I've done wiring and installations before in my house, and I've always worked with the breaker off.
    A year ago, I had a new ceiling put up in my dining room. When the workmen took down the chandelier, they didn't turn off the breaker, they just turned off the light switch. I asked the guy about it and he said there was no danger since the switch was off.
    Was he right or was he taking a risk?







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  4. #4
    Eruption Yerfdog's Avatar
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    Quote Originally Posted by Bullwinkle View Post
    Thanks Yerf, it's reassuring to hear from an expert. Everything I know, I learned from a Black and Decker book I bought at Lowe's.

    This leads me to another question if you have time:

    What's up with the 39 volts? Can I still get zapped? I guess I don't understand this "potential" part.

    I've done wiring and installations before in my house, and I've always worked with the breaker off.
    A year ago, I had a new ceiling put up in my dining room. When the workmen took down the chandelier, they didn't turn off the breaker, they just turned off the light switch. I asked the guy about it and he said there was no danger since the switch was off.
    Was he right or was he taking a risk?
    First of all, it's an older house (30 years, I believe you said). The switch circuit is likely called a switch loop, which is a common method - there are other devices wired into the circuit, I assume. You could rewire the whole thing, but it is NOT a dangerous situation. It is very common.

    The workmen were right and wrong. You should ALWAYS work with the breaker off, pro or not. I was working on an overhead door the other day (30 footer for locomotives, give or take. I went to great lengths to verify power was off - there was a "breaker" box about another 10 feet above the door, and I hate heights, especially working on a man-lift (wobble-wobble). The RIGHT part is that there is virtually no likelihood of injury from 39 volts in a house circuit - even with 110 you're likely only to feel a buzz, but why risk it.

    How exactly did you measure the 39 volts (give or take)? Was it wire to ground? Or to metal from a junction box where the fixture was? Not that it really matters, just curious.

    Potential...I guess the best explanation is that there is potential for a complete circuit, if a load (fan, light) is connected and a switch (or breaker) is closed. Without a light or fan in the circuit, and with the switch open, the circuit is not complete. Only the "potential" for a circuit exists. Now, if you physically complete the circuit (the one you measured with your meter) with,say two hands, you will complete the circuit and current will flow (through you). At 39 volts, you'll feel a little buzz. At 110, more so, but death will not likely ensue. If you close the switch, 110 will be available (potential) at those same two wires, and you have the opportunity to complete the circuit (with a fan, a light, or two hands if you so choose).

    If you noticed I said likely several times - I did so for a reason. My point is why would you risk it, as a novice? I wouldn't, and I've been doing it for years. Kill the breaker, remove the "likely".

    Does that help?
    I swear, it's like I'm playin' cards with my brother's kids or somethin'. You nerve-wrackin' sons-a-bitches.

  5. #5
    Sinner's Swing! Bullwinkle's Avatar
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    Quote Originally Posted by Yerfdog View Post

    How exactly did you measure the 39 volts (give or take)? Was it wire to ground? Or to metal from a junction box where the fixture was? Not that it really matters, just curious.

    I removed a light bulb from the fixture and put the probes inside the socket; one on the bottom of the socket and one on the side.
    I was just guessing that this is the way the current flows through a light bulb. I got a reading of 110v when the switch was on, so I figure I was right, but I really don't know.

    I'm totally ignorant about my meter. If I get some kind of numbers on the screen, I figure there's electricity flowing and I don't touch anything. If I get a reading of zero, I measure again every different way I can think of. If I still get zero, I say a little prayer and then start operating. I haven't started any fires yet with this measuring system of mine, but I do get nervous sometimes.

    In my house, I always know that nothing I do could be worse than what the previous owner(s) did to it. I spend much of my time undoing what was done before. Lots of my outlets were wired backwards and/or ungrounded and the attic was a nightmare. Everything was held together with electrical tape. Not a wire nut or box in sight!

    The house was built in '55 and it's wired for 220v. I was just guessing about the age of the switch. From the look of the wiring, some of it is original and some (the poorly-done stuff) is more recent.







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  6. #6
    Eruption Yerfdog's Avatar
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    If you'd like me to go into detail about why you're seeing 39 volts with the switch off, I can, but it's really unimportant. Work with the breaker off like you have, and verify that there is no voltage before you work. It seems like you're doing just fine.

    In that you're working in a switch loop circuit, one, not both of the "live" wires is disconnected when you "open" the switch. The other will have a part of the voltage (in this case, 39 volts) when measured. The other 80 or so volts are being stopped at the switch, for lack of a better explanation. When the breaker is open, neither side can be seen (no 39 volts, no other 80 volts), because the breaker completely disconnects both sides of source voltage, vice just one side (39 or 80 volts).

    The bottom line is open the breaker, verify no voltage at the location you intend to work. You are doing fine.

    Lemme know if you have any other questions.
    I swear, it's like I'm playin' cards with my brother's kids or somethin'. You nerve-wrackin' sons-a-bitches.

  7. #7
    Sinner's Swing! Bullwinkle's Avatar
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    Quote Originally Posted by Yerfdog View Post
    If you'd like me to go into detail about why you're seeing 39 volts with the switch off, I can, but it's really unimportant. Work with the breaker off like you have, and verify that there is no voltage before you work. It seems like you're doing just fine.

    In that you're working in a switch loop circuit, one, not both of the "live" wires is disconnected when you "open" the switch. The other will have a part of the voltage (in this case, 39 volts) when measured. The other 80 or so volts are being stopped at the switch, for lack of a better explanation. When the breaker is open, neither side can be seen (no 39 volts, no other 80 volts), because the breaker completely disconnects both sides of source voltage, vice just one side (39 or 80 volts).

    The bottom line is open the breaker, verify no voltage at the location you intend to work. You are doing fine.

    Lemme know if you have any other questions.

    Okay. That makes sense. Thanks a lot.







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  8. #8
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    Default yerfdog

    funny this thread is here as i just had a problem...buddy replaced 15 amp breaker with a 20 amp breaker...house is 26 years old and microwave quit working without tripping breaker...is it because you are not supposed to do this?

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    Eruption Yerfdog's Avatar
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    First thought - breaker bad/miswired.

    Is Mwave hard wired, or plugged in to outlet?

    Going from a 15 amp to a 20 amp breaker should not be the problem.

    Edit - please clarify "quit working".
    I swear, it's like I'm playin' cards with my brother's kids or somethin'. You nerve-wrackin' sons-a-bitches.

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    it got very very hot and just quit...so went online and searched the term "can you replace a 15 amp breaker with a 20" and it came back with the answer that the wiring for a 15 amp breaker cannot support the juice coming from a 20 amp breaker...so i made him come back and put 15 amp back in and so far everything seems fine...it said something about the gauge of the 15 amp wiring could get very hot and start a fire in wall...

    if that is not the case i owe him an apology for making him come back...however i did talk to an electrical engineer in the meantime and he said that replacing a 15 amp breaker with a 20 is very stupid and risky...just wanted to see what you thought...

    this all happened less than a hour ago..

  11. #11
    Eruption Yerfdog's Avatar
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    Quote Originally Posted by buster65 View Post
    it got very very hot and just quit...so went online and searched the term "can you replace a 15 amp breaker with a 20" and it came back with the answer that the wiring for a 15 amp breaker cannot support the juice coming from a 20 amp breaker...so i made him come back and put 15 amp back in and so far everything seems fine...it said something about the gauge of the 15 amp wiring could get very hot and start a fire in wall...

    if that is not the case i owe him an apology for making him come back...however i did talk to an electrical engineer in the meantime and he said that replacing a 15 amp breaker with a 20 is very stupid and risky...just wanted to see what you thought...

    this all happened less than a hour ago..
    So you're saying he put a 15 amp breaker back in an everything (the mwave) works again?

    The wiring in a house should easily be able to handle either the 15 or 20 amp breakers supply. This sounds a little funny....

    The reason I say that is because the wires in question (from the breaker to the mwave) would not be drawing any more current after installing the new (20 amp) breaker, even if the wiring did not support that current (which I do not buy for even a second).

    Sounds more like a wiring mistake than anything else. What else is in the circuit?
    I swear, it's like I'm playin' cards with my brother's kids or somethin'. You nerve-wrackin' sons-a-bitches.

  12. #12
    Eruption Yerfdog's Avatar
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    Again, is the microwave hard wired? Circuitry for a microwave should be 20 amp service - most houses in the US use 20 amps for mwaves because they may draw up to the full 15 amps. You should verify that the wiring is sufficient to handle it - but I need to know whether it was hard wired or plugged into an outlet. Is it a newer or older house?
    I swear, it's like I'm playin' cards with my brother's kids or somethin'. You nerve-wrackin' sons-a-bitches.

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    kitchen lights etc...when he came back he said that if the wires were not able to handle the new 20 amp breaker that they would have melted (and i agree) i have no clue what may have happened but now that the 15 amp is back in everything is fine...


    here is just one of the links i found...funny that i am getting conflicting info from several different places...

    http://answers.yahoo.com/question/in...0220729AAXZB6s


    house 26 years old...
    Last edited by buster65; 08.30.09 at 06:17 PM. Reason: added age

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    Eruption Yerfdog's Avatar
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    Quote Originally Posted by Yerfdog View Post
    Again, is the microwave hard wired? ...but I need to know whether it was hard wired or plugged into an outlet.
    The key here is that code for a microwave should be 20 amp service, with the appropriate wiring (12 gauge, vice 14 gauge for a 15 amp service), but that's assuming the microwave is connected where and how it was intended to be connected.
    I swear, it's like I'm playin' cards with my brother's kids or somethin'. You nerve-wrackin' sons-a-bitches.

 

 

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