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Electricians and electrical minded folks... need an opinion

BigDanSBigDanS Senior MemberPosts: 6,992 Senior Member
My porch light is out. I replaced the switch even though it tested good on continuity and resistance. At the switch I get 117 v on my Fluke, but at the lamp end I get 15.3v or so. I tried a continuity test between the two and did not get tone. I am assuming a short?

It is in 1/2 inch conduit with 5 other wires. I really do not want to take it apart and repull the wire, especially in this heat, but I cannot think of anything else. I really don't know how it could have gone bad.

I would appreciate any thoughts / opinions.

D
"A patriot is mocked, scorned and hated; yet when his cause succeeds, all men will join him, for then it costs nothing to be a patriot." Mark Twain
Alcohol, Tobacco, Firearms and Explosives.... now who's bringing the hot wings? :jester:
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Replies

  • zorbazorba Senior Member Posts: 24,203 Senior Member
    Its not a short. Shorts blow fuses, trip breakers, and catch things on fire...

    Are you getting the 15.3v ACROSS the lamp, or from one side to ground? DVMs are not the best tool for electrical work like this, their impedance is too high and you get bogus readings on open circuits. I recommend a "Wiggie".

    You probably have an open wire - check the connection at the lamp socket.
    -Zorba, "The Veiled Male"

    "If you get it and didn't work for it, someone else worked for it and didn't get it..."
  • TeachTeach Senior Member Posts: 18,428 Senior Member
    You've got an open circuit, not a short, and no, there isn't another option I can think of except pulling a new wire.
    Jerry
  • Big ChiefBig Chief Senior Member Posts: 32,995 Senior Member
    Open? Bad ground at socket? Broken/loose neutral. Wire loose at lamp? Socket bad? Phantom Voltage may account for the 15 Volts AC.......

    Digital meter? Did it auto switch scales on you and is it set to AC Volts?
    It's only true if it's on this forum where opinions are facts and facts are opinions
    Words of wisdom from Big Chief: Flush twice, it's a long way to the Mess Hall
    I'd rather have my sister work in a whorehouse than own another Taurus!
  • Big ChiefBig Chief Senior Member Posts: 32,995 Senior Member
    Hey sometimes them wires come loose from the screws or where they are twisted together in the yellow/green/black caps.

    Especially if you let the lamp/fixture swing from them, don't ask how I know that :jester:
    It's only true if it's on this forum where opinions are facts and facts are opinions
    Words of wisdom from Big Chief: Flush twice, it's a long way to the Mess Hall
    I'd rather have my sister work in a whorehouse than own another Taurus!
  • Big ChiefBig Chief Senior Member Posts: 32,995 Senior Member
    I replaced the whole fixture on my porch last year because after replacing the bulb it still wouldn't come on, was motion/sensor lights. I farted around with the switch in the house before I figured out it was past there taking line V readings and resistance measurements with power/switches on and off and they checked good.............only thing left was the wiring and the fixture.
    It's only true if it's on this forum where opinions are facts and facts are opinions
    Words of wisdom from Big Chief: Flush twice, it's a long way to the Mess Hall
    I'd rather have my sister work in a whorehouse than own another Taurus!
  • BigDanSBigDanS Senior Member Posts: 6,992 Senior Member
    I crawled up in the roof , it goes to a junction box then to the lamp. I will have to go up in the AM with some tools and look at it.

    We had some roof leaks a couple years ago and it is possible it got wet and the wires are corroded. We have a new roof now and it is all in conduit, so it is hard to believe it it ever got chewed.

    Switch has 117v 15 amps at the hot side and switched side. The switched side is a yellow wire. With the fixture off I get 15.3 v 15 amps at the yellow wire with the tester grounded to the conduit or the neutral. It's 120 F up there right now and a ton of insulation. I can cut it at the breaker and check it in the AM.

    Any other advice? Thanks!

    D
    "A patriot is mocked, scorned and hated; yet when his cause succeeds, all men will join him, for then it costs nothing to be a patriot." Mark Twain
    Alcohol, Tobacco, Firearms and Explosives.... now who's bringing the hot wings? :jester:
  • Big ChiefBig Chief Senior Member Posts: 32,995 Senior Member
    How are you taking current readings, does you meter have a clamp on feature or are you breaking the circuit and putting the meter in series to read it?
    It's only true if it's on this forum where opinions are facts and facts are opinions
    Words of wisdom from Big Chief: Flush twice, it's a long way to the Mess Hall
    I'd rather have my sister work in a whorehouse than own another Taurus!
  • Farm Boy DeuceFarm Boy Deuce Senior Member Posts: 6,083 Senior Member
    If you are drawing 15A off of one fixture you have a problem, like bad. If I understand you correctly the 15V you are seeing AT the fixture with the switch OFF. If I understand you, that is just induced voltage from the conduit. You need to check voltage at the terminals on the back of the fixture.

    Right now it sounds like you have a bad connection, probably on the neutral.
    I am afraid we forget sometime that the basic and simple things brings us the most pleasure.
    Dad 5-31-13
  • Big ChiefBig Chief Senior Member Posts: 32,995 Senior Member
    Don't worry about the Amps or Current readings............ household lines have 15-20 AMP ratings and the breakers in your fuse box are rated to handle that amount and will trip when exceeded.

    Be sure the switch is off at the wall and the circuit breaker is flipped off/pulled at the box before you go touching any wires.

    It is probably something simple.
    It's only true if it's on this forum where opinions are facts and facts are opinions
    Words of wisdom from Big Chief: Flush twice, it's a long way to the Mess Hall
    I'd rather have my sister work in a whorehouse than own another Taurus!
  • BigDanSBigDanS Senior Member Posts: 6,992 Senior Member
    So inspired by you all I crawled into the attic space and tracked down the junction box. I am a network wiring guy and can look at 100 Cat5e connections and trace them, but this box has a squirrel nest of wires in different colors. I suppose since this house was owned by an electrician he would do something like this. My Fluke meter shows me volts and has a strength bar underneath that shows amps available.

    At the switch side power in and power out to the yellow side shows 117 v and 15 amps available to ground. At the lamp side it now shows about 17v and 15 amps available on the yellow wire.

    I found the wires but it doesn't make sense to me yet. The yellow wire from the switch is twist connected in attic junction box to a brown wire that leaves the junction box in a Romex cable. I could not trace where it went after going under three sets of trusses and insulation. The yellow wire from the lamp comes into the same junction box and is twist connected to a black wire on the same piece of Romex. It isn't a three way switch and I don't know where it goes or terminates. If the black and brown wires aren't twisted down the line it must be the problem.

    On the other hand I had an adventure and remember why I don't do this.

    2F4AF109-99D5-4DB9-913F-5A8DBDB5D0A6_zpswyooh9yx.jpg

    I am soaking wet from 20 minutes in the hole and 120 F temps and covered in insulation. I think the electrician will be here Monday and he can sort it out with three other projects... I am going to get a shower! Ugh!!!

    D
    "A patriot is mocked, scorned and hated; yet when his cause succeeds, all men will join him, for then it costs nothing to be a patriot." Mark Twain
    Alcohol, Tobacco, Firearms and Explosives.... now who's bringing the hot wings? :jester:
  • BigDanSBigDanS Senior Member Posts: 6,992 Senior Member
    Chris, I am a professional, but I do low voltage and computer stuff. FWIW, I have been playing with electronics over 45 years, since my father had a TV repair shop from the time I was born until he died in 1985.

    Here's a picture of my meter display plugged into a wall socket. Notice the bar at the bottom of the readings, goes from 0 to 30 amps. Most home circuits are 15 amps.

    0099B2F8-BD73-47BB-9E95-E26F048107AB_zpsfbq2klnf.jpg

    But I agree with you, I am hiring a young buck that does this for a living to fix three problems.

    D
    "A patriot is mocked, scorned and hated; yet when his cause succeeds, all men will join him, for then it costs nothing to be a patriot." Mark Twain
    Alcohol, Tobacco, Firearms and Explosives.... now who's bringing the hot wings? :jester:
  • zorbazorba Senior Member Posts: 24,203 Senior Member
    CPJ's right, its a voltage bar graph. The only way it could display "potential amperage" would be to load the circuit until the breaker blew, you'd get spectacular arcing when you probed the circuit at the very least! DVMs just aren't the best tool for line voltage work anyway.
    -Zorba, "The Veiled Male"

    "If you get it and didn't work for it, someone else worked for it and didn't get it..."
  • BigDanSBigDanS Senior Member Posts: 6,992 Senior Member
    zorba wrote: »
    CPJ's right, its a voltage bar graph. The only way it could display "potential amperage" would be to load the circuit until the breaker blew, you'd get spectacular arcing when you probed the circuit at the very least! DVMs just aren't the best tool for line voltage work anyway.

    I looked this up on the Fluke site and sure enough I am wrong and have been wrong for many years. Thank you for the clarification all! Further proof I need a pro.

    D
    "A patriot is mocked, scorned and hated; yet when his cause succeeds, all men will join him, for then it costs nothing to be a patriot." Mark Twain
    Alcohol, Tobacco, Firearms and Explosives.... now who's bringing the hot wings? :jester:
  • Big ChiefBig Chief Senior Member Posts: 32,995 Senior Member
    http://www.manualslib.com/manual/730798/Fluke-77.html?page=13

    Using the Bar Graph
    The bar graph is like the needle on an analog Meter. There is an
    overload indicator ( ) to the right, and a polarity indicator ( ) to the
    left.
    Because the bar graph is much faster than the digital display, the
    bar graph is useful for making peak and null adjustments, and for
    observing rapidly changing inputs.
    It's only true if it's on this forum where opinions are facts and facts are opinions
    Words of wisdom from Big Chief: Flush twice, it's a long way to the Mess Hall
    I'd rather have my sister work in a whorehouse than own another Taurus!
  • Big ChiefBig Chief Senior Member Posts: 32,995 Senior Member
    Ha, read the owners manual..............I have to look in my glove box for the owners manual to figure what those so called international dash indicators are supposed to mean. Wiper fluid low, I thought a light had went out............
    It's only true if it's on this forum where opinions are facts and facts are opinions
    Words of wisdom from Big Chief: Flush twice, it's a long way to the Mess Hall
    I'd rather have my sister work in a whorehouse than own another Taurus!
  • VarmintmistVarmintmist Senior Member Posts: 7,541 Senior Member
    One quick way to find out. Pull the power and short and ground both wires at one end. Go to the other end and read each side to ground. You should read about the same resistance on each leg, if it is different then you have a partial open, if one leg doesnt read to ground, then you have a open. Called a third leg test.

    Power off, everything disconnected.

    Do you have a switched outlet on the porch?
    It's boring, and your lack of creativity knows no bounds.
  • Farm Boy DeuceFarm Boy Deuce Senior Member Posts: 6,083 Senior Member
    cpj wrote: »
    For my prediction, your wet (at one time) Jbox is where the demon lies. I seriously doubt a wire is broken. Especially in conduit. I'd wager there will be a loose/corroded connection somewhere.

    This. The only spot I would check before this is the terminals on the fixture. In closed up spaces the heat will eventually cause issues, especially with porcelain sockets.
    I am afraid we forget sometime that the basic and simple things brings us the most pleasure.
    Dad 5-31-13
  • BigDanSBigDanS Senior Member Posts: 6,992 Senior Member
    In looking at this, I can't understand where the Romex goes. Perhaps at one time there was another light on the north side of the house but it doesn't make sense to wire in series instead of parallel. The neutrals are all twisted up properly, but the power leg is odd. I will have my guy Elvis look at it. It could be as simple as abandoning the Romex and twisting the two yellow wires together. I am just perplexed why that was done.

    Thanks all for the opinions and correcting my stupidity!

    D
    "A patriot is mocked, scorned and hated; yet when his cause succeeds, all men will join him, for then it costs nothing to be a patriot." Mark Twain
    Alcohol, Tobacco, Firearms and Explosives.... now who's bringing the hot wings? :jester:
  • BigDanSBigDanS Senior Member Posts: 6,992 Senior Member
    This. The only spot I would check before this is the terminals on the fixture. In closed up spaces the heat will eventually cause issues, especially with porcelain sockets.

    The fixture tests fine. I put a bulb in, connect both wires and get a continuity positive from the meter, and no continuity with the bulb removed. I am actually replacing the fixture with a new decorative one.

    FWIW, all this is for putting the house on the market for sale. Trying to correct the little BS issues.

    D
    "A patriot is mocked, scorned and hated; yet when his cause succeeds, all men will join him, for then it costs nothing to be a patriot." Mark Twain
    Alcohol, Tobacco, Firearms and Explosives.... now who's bringing the hot wings? :jester:
  • earlyearly Senior Member Posts: 4,950 Senior Member
    Im guessing that the upper most portions of the house are quite hot :jester:
    My thoughts are generally clear. My typing, not so much.
  • Farm Boy DeuceFarm Boy Deuce Senior Member Posts: 6,083 Senior Member
    Take the Romex out of it altogether. Put the wires you KNOW go to the light together. If it works figure out where the Romex goes when something doesn't work.
    I am afraid we forget sometime that the basic and simple things brings us the most pleasure.
    Dad 5-31-13
  • Big ChiefBig Chief Senior Member Posts: 32,995 Senior Member
    You are not stupid, just not used to working with household wiring which can be a real pisser at first.

    A few simple wires right? How hard can it be?

    Even with experience working with electronics with much more sophisticated circuity it is a different ballgame. What little I know about it I had to learn starting with looking up what comes off the powder pole outside to my house, my meter outside, my D-Square breaker box and how it is distributed and returned and how the 120 and 220 lines work.............I still am far from knowledgeable on residential electrical stuff..........some basic stuff don't change and can be applied, but you are working with AC where you live and a mistake can be deadly to you, cause a fire or get a loved one or yourself shocked/ electrocuted if you don't pay attention to what you are doing and know when to call an expert in like you are.

    I'm not afraid of electricity,. just have a deep respect for it.
    It's only true if it's on this forum where opinions are facts and facts are opinions
    Words of wisdom from Big Chief: Flush twice, it's a long way to the Mess Hall
    I'd rather have my sister work in a whorehouse than own another Taurus!
  • Big ChiefBig Chief Senior Member Posts: 32,995 Senior Member
    Yep and don't take the labels on the junction box fer granted...........like cpj said never know what the previous owner did or didn't do or if he cut corners or added/removed something not to code............
    It's only true if it's on this forum where opinions are facts and facts are opinions
    Words of wisdom from Big Chief: Flush twice, it's a long way to the Mess Hall
    I'd rather have my sister work in a whorehouse than own another Taurus!
  • zorbazorba Senior Member Posts: 24,203 Senior Member
    cpj wrote: »
    Your last sentence. I call bull crap. Welcome to the 1980s, it's nice here. :tooth:

    Impedance is too high - you have the same problems with a VTVM or a FET VOM on line voltage - too many false readings. Wiggie is where its at! High impedance meter is fine - as long as you're reading a live circuit. Dead circuits have too many "ghost" readings. Just like a logic probe is often better than a 'scope - the scope doesn't know the difference between ground and open (although there are ways around that).
    -Zorba, "The Veiled Male"

    "If you get it and didn't work for it, someone else worked for it and didn't get it..."
  • zorbazorba Senior Member Posts: 24,203 Senior Member
    cpj wrote: »
    For my prediction, your wet (at one time) Jbox is where the demon lies. I seriously doubt a wire is broken. Especially in conduit. I'd wager there will be a loose/corroded connection somewhere.

    That's where my money would be. Maybe even at the light socket itself, depending on how/where the voltage reading was taken.
    -Zorba, "The Veiled Male"

    "If you get it and didn't work for it, someone else worked for it and didn't get it..."
  • Big Al1Big Al1 Senior Member Posts: 8,064 Senior Member
    I don't like to sweat!! I just call the "guy" and let him sweat for me!
  • snake284snake284 Senior Member Posts: 22,394 Senior Member
    BigDanS wrote: »
    I crawled up in the roof , it goes to a junction box then to the lamp. I will have to go up in the AM with some tools and look at it.

    We had some roof leaks a couple years ago and it is possible it got wet and the wires are corroded. We have a new roof now and it is all in conduit, so it is hard to believe it it ever got chewed.

    Switch has 117v 15 amps at the hot side and switched side. The switched side is a yellow wire. With the fixture off I get 15.3 v 15 amps at the yellow wire with the tester grounded to the conduit or the neutral. It's 120 F up there right now and a ton of insulation. I can cut it at the breaker and check it in the AM.

    Any other advice? Thanks!

    D

    Call an Electrician!
    Daddy, what's an enabler?
    Son that's somebody with nothing to do with his time but keep me in trouble with mom.
  • zorbazorba Senior Member Posts: 24,203 Senior Member
    cpj wrote: »
    Guess who else thinks the wiggy sucks?
    Everyone. That's why they were crap canned.
    One thing that you CANT do with one is measure from hot to ground on a GFCI outlet. But it's damn fun to tell the apprentice to try....
    I'll have to remember that - I occasionally have the opportunity... :rotflmao:
    -Zorba, "The Veiled Male"

    "If you get it and didn't work for it, someone else worked for it and didn't get it..."
  • zorbazorba Senior Member Posts: 24,203 Senior Member
    You can always use my late father's technique - lifetime IBEW electrician: Touch the wires between thumb and pinky! He was calibrated, he could tell 110 from 220, from 277, from 308 3 phase (which he said hurt like a mother!). He had enormous, thick callouses on his hands from pulling wire his entire life - they didn't conduct very well so he was able to get away with this - not that I'd recommend it.

    And uh, you don't use a wiggie for continuity...
    -Zorba, "The Veiled Male"

    "If you get it and didn't work for it, someone else worked for it and didn't get it..."
  • zorbazorba Senior Member Posts: 24,203 Senior Member
    cpj wrote: »
    Aka Neon tester. Touch one lead with your finger, the other to the hot. The neon would glow slightly. But wouldn't when you touched the neutral or ground.

    I remember those!
    -Zorba, "The Veiled Male"

    "If you get it and didn't work for it, someone else worked for it and didn't get it..."
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