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#1
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Fixed my porch light, not sure how
The back porch light stopped working, a new bulb didn't help.
So. I put a meter on the socket. 0 V. I pulled the switch plate off (just a normal single pole). 80 V terminal to terminal. Hmmm? Killed the power, put an ohmeter terminal to terminal, infinite resistance at both switch positions. Diagnosis bad switch, supported by the fact that before it died completely, flipping the switch several times made it work. Besides I've always had a CFL in that one and I suspect the capacitor shortens the switch life due to arcing. Okay, a new switch is $1.29, no big loss if wrong. Took the old switch off, turned the power back on and checked wire to wire just for grins, still 80 V. Uh oh. Put the new switch in. Turned power on, checked the socket, 120 V. Put bulb in, (CFL), lights up fine. Well, I have a working porch light again, but I'm left with the 80 V mystery. I don't know any way to get 80 V on a normal residential power setup. The meter was a digital Radio Shack multimeter. If I'd had time I'd have checked again with the Simpson analog, digitals sometimes give funny readings, but I've never seen 80 V. What am I missing? |
#2
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Fixed my porch light, not sure how
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#3
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Fixed my porch light, not sure how
On May 15, 7:40*pm, Sjouke Burry s@b wrote:
A bad contact somewhere? Not sure that makes sense. Pulling a current across a resistance, like from a bad connection, should cause a voltage drop. But no-load open circuit should be full voltage. |
#4
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Fixed my porch light, not sure how
On Tue, 15 May 2012 17:07:58 -0700 (PDT), TimR
wrote: On May 15, 7:40Â*pm, Sjouke Burry s@b wrote: A bad contact somewhere? Not sure that makes sense. Pulling a current across a resistance, like from a bad connection, should cause a voltage drop. But no-load open circuit should be full voltage. OP said they measured across the switch. Learn how to use a meter for troubleshooting, and what the reading mean. The problem IS FIXED. There was a BAD SWITCH. |
#5
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Fixed my porch light, not sure how
On May 15, 8:07*pm, TimR wrote:
On May 15, 7:40*pm, Sjouke Burry s@b wrote: A bad contact somewhere? Not sure that makes sense. Pulling a current across a resistance, like from a bad connection, should cause a voltage drop. *But *no-load open circuit should be full voltage. You were pulling a current through that circuit and it had two resistances in it. One presumably was the light bulb, otherwise measuring from terminal to terminal of the open switch should not read anything.. The other resistance is that of the multimeter itself. How much of the 120V in the circuit appears across the bulb and how much across the multimeter is proportional to their resistance. I would expect the multimeter to have such a high resistance that you'd read close to 120V. But with a CFL presented with a tiny current, not able to light, who knows what that resistance/impedance is. |
#6
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Fixed my porch light, not sure how
On 15 May 2012 23:40:33 GMT, Sjouke Burry s@b wrote:
TimR wrote in news:2fad4ded-a0ce-4fae-9166- : The back porch light stopped working, a new bulb didn't help. So. I put a meter on the socket. 0 V. I pulled the switch plate off (just a normal single pole). 80 V terminal to terminal. Hmmm? Killed the power, put an ohmeter terminal to terminal, infinite resistance at both switch positions. Diagnosis bad switch, supported by the fact that before it died completely, flipping the switch several times made it work. Besides I've always had a CFL in that one and I suspect the capacitor shortens the switch life due to arcing. Okay, a new switch is $1.29, no big loss if wrong. Took the old switch off, turned the power back on and checked wire to wire just for grins, still 80 V. Uh oh. Put the new switch in. Turned power on, checked the socket, 120 V. Put bulb in, (CFL), lights up fine. Well, I have a working porch light again, but I'm left with the 80 V mystery. I don't know any way to get 80 V on a normal residential power setup. The meter was a digital Radio Shack multimeter. If I'd had time I'd have checked again with the Simpson analog, digitals sometimes give funny readings, but I've never seen 80 V. What am I missing? A bad contact somewhere? Put a heavy load, an iron or vacuum cleaner on it to make sure there is a solid feed. If those work, stop worrying. If not, start worrying, and start checking backward along the feed. A lousy job, but loose contacts can cause a fire. Just learn how to use the meter. |
#7
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Fixed my porch light, not sure how
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#8
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Fixed my porch light, not sure how
TimR wrote:
The back porch light stopped working, a new bulb didn't help. So. I put a meter on the socket. 0 V. I pulled the switch plate off (just a normal single pole). 80 V terminal to terminal. Hmmm? Killed the power, put an ohmeter terminal to terminal, infinite resistance at both switch positions. Diagnosis bad switch, supported by the fact that before it died completely, flipping the switch several times made it work. Besides I've always had a CFL in that one and I suspect the capacitor shortens the switch life due to arcing. Okay, a new switch is $1.29, no big loss if wrong. Took the old switch off, turned the power back on and checked wire to wire just for grins, still 80 V. Uh oh. Put the new switch in. Turned power on, checked the socket, 120 V. Put bulb in, (CFL), lights up fine. Well, I have a working porch light again, but I'm left with the 80 V mystery. I don't know any way to get 80 V on a normal residential power setup. The meter was a digital Radio Shack multimeter. If I'd had time I'd have checked again with the Simpson analog, digitals sometimes give funny readings, but I've never seen 80 V. What am I missing? An old analog would likely show different voltages with each range. Carbon in switch ?? Greg |
#9
Posted to alt.home.repair,sci.engr.lighting
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Fixed my porch light, not sure how
TimR wrote:
The back porch light stopped working, a new bulb didn't help. So. I put a meter on the socket. 0 V. I pulled the switch plate off (just a normal single pole). 80 V terminal to terminal. Hmmm? Killed the power, put an ohmeter terminal to terminal, infinite resistance at both switch positions. Diagnosis bad switch, supported by the fact that before it died completely, flipping the switch several times made it work. Besides I've always had a CFL in that one and I suspect the capacitor shortens the switch life due to arcing. Okay, a new switch is $1.29, no big loss if wrong. Took the old switch off, turned the power back on and checked wire to wire just for grins, still 80 V. Uh oh. Put the new switch in. Turned power on, checked the socket, 120 V. Put bulb in, (CFL), lights up fine. Well, I have a working porch light again, but I'm left with the 80 V mystery. I don't know any way to get 80 V on a normal residential power setup. The meter was a digital Radio Shack multimeter. If I'd had time I'd have checked again with the Simpson analog, digitals sometimes give funny readings, but I've never seen 80 V. What am I missing? You cannot believe the accuracy of a multimeter with no load on the circuit. The reason is too complicated to divulge here, but it's a fact. If your meter reads anything above about five volts - when it should be 120 - it really IS 120. |
#10
Posted to alt.home.repair,sci.engr.lighting
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Fixed my porch light, not sure how
On Tue, 15 May 2012 19:57:53 -0500, "HeyBub"
wrote: TimR wrote: The back porch light stopped working, a new bulb didn't help. So. I put a meter on the socket. 0 V. I pulled the switch plate off (just a normal single pole). 80 V terminal to terminal. Hmmm? Killed the power, put an ohmeter terminal to terminal, infinite resistance at both switch positions. Diagnosis bad switch, supported by the fact that before it died completely, flipping the switch several times made it work. Besides I've always had a CFL in that one and I suspect the capacitor shortens the switch life due to arcing. Okay, a new switch is $1.29, no big loss if wrong. Took the old switch off, turned the power back on and checked wire to wire just for grins, still 80 V. Uh oh. Put the new switch in. Turned power on, checked the socket, 120 V. Put bulb in, (CFL), lights up fine. Well, I have a working porch light again, but I'm left with the 80 V mystery. I don't know any way to get 80 V on a normal residential power setup. The meter was a digital Radio Shack multimeter. If I'd had time I'd have checked again with the Simpson analog, digitals sometimes give funny readings, but I've never seen 80 V. What am I missing? You cannot believe the accuracy of a multimeter with no load on the circuit. The reason is too complicated to divulge here, but it's a fact. If your meter reads anything above about five volts - when it should be 120 - it really IS 120. The OP stated "I pulled the switch plate off (just a normal single pole). 80 V terminal to terminal. Hmmm?" What's wrong with this situation? What is being measured? What is indicated by the fact there is no voltage at the socket and 80 volts across the switch? Don't need to be a member of MENSA to figure this one out. The voltage reading is likely accurate - accurate enough, anyway. Just so happens it is immaterial because it is not a valid measurement. The voltmeter was being used as an ammeter instead of a voltmeter. |
#11
Posted to alt.home.repair,sci.engr.lighting
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Fixed my porch light, not sure how
"TimR" wrote in message ... The back porch light stopped working, a new bulb didn't help. So. I put a meter on the socket. 0 V. I pulled the switch plate off (just a normal single pole). 80 V terminal to terminal. Hmmm? Killed the power, put an ohmeter terminal to terminal, infinite resistance at both switch positions. Diagnosis bad switch, supported by the fact that before it died completely, flipping the switch several times made it work. Besides I've always had a CFL in that one and I suspect the capacitor shortens the switch life due to arcing. Okay, a new switch is $1.29, no big loss if wrong. Took the old switch off, turned the power back on and checked wire to wire just for grins, still 80 V. Uh oh. Put the new switch in. Turned power on, checked the socket, 120 V. Put bulb in, (CFL), lights up fine. Well, I have a working porch light again, but I'm left with the 80 V mystery. I don't know any way to get 80 V on a normal residential power setup. The meter was a digital Radio Shack multimeter. If I'd had time I'd have checked again with the Simpson analog, digitals sometimes give funny readings, but I've never seen 80 V. What am I missing? It is often normal to get strange readings with a digital meter, as someone said, too much to go into here. Short answer is the wiring is acting like a capacitor or transformer and the high impedance of the meter is picking up voltage with a very small current. Almost any load and the voltage will dissapear.. If the bulb was still in the circuit, it may be a small ammount of feed through in the CFL. |
#12
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Fixed my porch light, not sure how
On Tue, 15 May 2012 21:14:57 -0400, "Ralph Mowery"
wrote: "TimR" wrote in message ... The back porch light stopped working, a new bulb didn't help. So. I put a meter on the socket. 0 V. I pulled the switch plate off (just a normal single pole). 80 V terminal to terminal. Hmmm? Killed the power, put an ohmeter terminal to terminal, infinite resistance at both switch positions. Diagnosis bad switch, supported by the fact that before it died completely, flipping the switch several times made it work. Besides I've always had a CFL in that one and I suspect the capacitor shortens the switch life due to arcing. Okay, a new switch is $1.29, no big loss if wrong. Took the old switch off, turned the power back on and checked wire to wire just for grins, still 80 V. Uh oh. Put the new switch in. Turned power on, checked the socket, 120 V. Put bulb in, (CFL), lights up fine. Well, I have a working porch light again, but I'm left with the 80 V mystery. I don't know any way to get 80 V on a normal residential power setup. The meter was a digital Radio Shack multimeter. If I'd had time I'd have checked again with the Simpson analog, digitals sometimes give funny readings, but I've never seen 80 V. What am I missing? It is often normal to get strange readings with a digital meter, as someone said, too much to go into here. Short answer is the wiring is acting like a capacitor or transformer and the high impedance of the meter is picking up voltage with a very small current. Almost any load and the voltage will dissapear.. If the bulb was still in the circuit, it may be a small ammount of feed through in the CFL. Short answer is the voltmeter was not being used properly, and the longer answer is nobody else here caught it. Nothing to do with inacuracies of digital meters - totally a case of not knowing how to use a meter to troubleshoot - or knowing how to interpret the readings when the meter is mis-connected. The readings are accurate |
#13
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Fixed my porch light, not sure how
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#15
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Fixed my porch light, not sure how
On Wed, 16 May 2012 08:08:54 -0600, bud--
wrote: On 5/16/2012 5:48 AM, HeyBub wrote: wrote: It is often normal to get strange readings with a digital meter, as someone said, too much to go into here. Short answer is the wiring is acting like a capacitor or transformer and the high impedance of the meter is picking up voltage with a very small current. Almost any load and the voltage will dissapear.. If the bulb was still in the circuit, it may be a small ammount of feed through in the CFL. Short answer is the voltmeter was not being used properly, and the longer answer is nobody else here caught it. Nothing to do with inacuracies of digital meters - totally a case of not knowing how to use a meter to troubleshoot - or knowing how to interpret the readings when the meter is mis-connected. The readings are accurate The readings are NOT accurate. The indicated voltage is a phantom. Consider your assertion that the meter is "mis-connected:" The meter has two probes. There are two wires. There are two and only two possible ways to connect the meter and the wires. Which of the two, according to you, is the correct way to connect all this stuff? If both of the two possibilities yield the same result, where is the "mis-connection"? The OP was measuring across an open switch with no load (no bulb). One might expect zero volts. What was measured was a "phantom" voltage, as Hey says, caused by capacitance between switched and neutral wires to the light and the high impedance of the meter as Ralph said. It is a rather well know quirk (inaccuracy) of digital meters. Except the OP had a CFL in the socket when they tested the voltage across the switch. The measurement across the switch would be meaningful with an incandescent bulb installed. Or a low impedance meter would measure zero volts (which would tell the OP nothing). Because the meter was, as I said, misconnected for the rquired test. |
#16
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Fixed my porch light, not sure how
On May 16, 7:48*am, "HeyBub" wrote:
wrote: It is often normal to get strange readings with a digital meter, as someone said, too much to go into here. *Short answer is the wiring is acting like a capacitor or transformer and the high impedance of the meter is picking up voltage with a very small current. *Almost any load and the voltage will dissapear.. *If the bulb was still in the circuit, it may be a small ammount of feed through in the CFL. Short answer is the voltmeter was not being used properly, and the longer answer is nobody else here caught it. Nothing to do with inacuracies of digital meters - totally a case of not knowing how to use a meter to troubleshoot - *or knowing how to interpret the readings when the meter is mis-connected. The readings are accurate The readings are NOT accurate. The indicated voltage is a phantom. Consider your assertion that the meter is "mis-connected:" The meter has two probes. There are two wires. There are two and only two possible ways to connect the meter and the wires. Which of the two, according to you, is the correct way to connect all this stuff? If both of the two possibilities yield the same result, where is the "mis-connection"?- Hide quoted text - - Show quoted text - I would have tested for 120V using one test lead on the light side of the switch and the other held to ground. I'd use ground because that's usually there and available without taking anything apart. Or he could have tested from the light side of the switch to neutral. |
#17
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Fixed my porch light, not sure how
wrote in message ... I would have tested for 120V using one test lead on the light side of the switch and the other held to ground. I'd use ground because that's usually there and available without taking anything apart. Or he could have tested from the light side of the switch to neutral. Many times there is no neutral at the light switch or if it is, it is not broken and easy to get a meter lead on. I also try not to test to ground as sometimes the ground wire is left out. |
#18
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Fixed my porch light, not sure how
On Wed, 16 May 2012 08:31:57 -0700 (PDT), "
wrote: On May 16, 7:48Â*am, "HeyBub" wrote: wrote: It is often normal to get strange readings with a digital meter, as someone said, too much to go into here. Â*Short answer is the wiring is acting like a capacitor or transformer and the high impedance of the meter is picking up voltage with a very small current. Â*Almost any load and the voltage will dissapear.. Â*If the bulb was still in the circuit, it may be a small ammount of feed through in the CFL. Short answer is the voltmeter was not being used properly, and the longer answer is nobody else here caught it. Nothing to do with inacuracies of digital meters - totally a case of not knowing how to use a meter to troubleshoot - Â*or knowing how to interpret the readings when the meter is mis-connected. The readings are accurate The readings are NOT accurate. The indicated voltage is a phantom. Consider your assertion that the meter is "mis-connected:" The meter has two probes. There are two wires. There are two and only two possible ways to connect the meter and the wires. Which of the two, according to you, is the correct way to connect all this stuff? If both of the two possibilities yield the same result, where is the "mis-connection"?- Hide quoted text - - Show quoted text - I would have tested for 120V using one test lead on the light side of the switch and the other held to ground. I'd use ground because that's usually there and available without taking anything apart. Or he could have tested from the light side of the switch to neutral. Correct. |
#19
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Fixed my porch light, not sure how
On Wed, 16 May 2012 06:48:49 -0500, "HeyBub"
wrote: wrote: It is often normal to get strange readings with a digital meter, as someone said, too much to go into here. Short answer is the wiring is acting like a capacitor or transformer and the high impedance of the meter is picking up voltage with a very small current. Almost any load and the voltage will dissapear.. If the bulb was still in the circuit, it may be a small ammount of feed through in the CFL. Short answer is the voltmeter was not being used properly, and the longer answer is nobody else here caught it. Nothing to do with inacuracies of digital meters - totally a case of not knowing how to use a meter to troubleshoot - or knowing how to interpret the readings when the meter is mis-connected. The readings are accurate The readings are NOT accurate. The indicated voltage is a phantom. Consider your assertion that the meter is "mis-connected:" The meter has two probes. There are two wires. There are two and only two possible ways to connect the meter and the wires. Which of the two, according to you, is the correct way to connect all this stuff? If both of the two possibilities yield the same result, where is the "mis-connection"? OK Bub - I'm make it REAL simple. And I'll type slowly so you can understand. A switch is in series with the load. The switch has 2 contacts. Both contacts are on the "live" wire, because the neutral is not switched. The OP measured the voltage from one terminal of the switch to the other. IF the bulb was not in the socket, the voltage would be ZERO, with the switch on or off. If there was an incandescent bulb in the socket, the voltage would be line voltage - roughly 120 volts, with the switch OFF, and ZERO with the switch on. - if the switch was any good. However, the OP had a CFL in the socket, so thecapacitance etc. of the electronic ballast was dropping about 40 volts across it with the extremely low current flowing through the meter - and because the switch was shot, the reading was the same both ways. If the switch had been good, he would have found 80 volts across the open switch, and ZERO across the closed switch, with the CFL lit. The CORRECT way to test the line voltage is line to neutral, or line to ground. If there is any ground at all the digital meter will read the same either way, within a tenth of a volt, I happen to have made my living using test meters for quite a few years, so I knowwhat the OP did, what he should have done, and exactly what the meter readings he gor mean. You obviously do not. |
#20
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Fixed my porch light, not sure how
On Tue, 15 May 2012 16:21:14 -0700 (PDT), TimR
wrote: The back porch light stopped working, a new bulb didn't help. So. I put a meter on the socket. 0 V. I pulled the switch plate off (just a normal single pole). 80 V terminal to terminal. Hmmm? Killed the power, put an ohmeter terminal to terminal, infinite resistance at both switch positions. Diagnosis bad switch, supported by the fact that before it died completely, flipping the switch several times made it work. Besides I've always had a CFL in that one and I suspect the capacitor shortens the switch life due to arcing. Okay, a new switch is $1.29, no big loss if wrong. Took the old switch off, turned the power back on and checked wire to wire just for grins, still 80 V. Uh oh. Put the new switch in. Turned power on, checked the socket, 120 V. Put bulb in, (CFL), lights up fine. Well, I have a working porch light again, but I'm left with the 80 V mystery. I don't know any way to get 80 V on a normal residential power setup. The meter was a digital Radio Shack multimeter. If I'd had time I'd have checked again with the Simpson analog, digitals sometimes give funny readings, but I've never seen 80 V. What am I missing? 80 volts terminal to terminal on the switch means 80 volt drop across the bulb. Same with switch o or off means the switch was no good. Feed to ground would read approxemately 120 volts. With bad switch load to ground would read zero. Good switch, load to ground 120. |
#21
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Fixed my porch light, not sure how
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#22
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Fixed my porch light, not sure how
On Wed, 16 May 2012 06:52:30 -0500, "HeyBub"
wrote: wrote: 80 volts terminal to terminal on the switch means 80 volt drop across the bulb. Same with switch o or off means the switch was no good. Feed to ground would read approxemately 120 volts. With bad switch load to ground would read zero. Good switch, load to ground 120. Huh? By definition, with a functioning switch energized, both sides MUST read the same and that "same" must be zero. With the switch in the OFF position, and using a digital voltmeter, you can get any reading from zero to 120. You don't read to good, Bub. I said from one terminal of the switch to GROUND or neutral. Live side th ground will always be aprox 120. Switched side to ground will be zero with the switch off, and 120 with the switch on, with a functioning switch, reguardless of load. Terminal to terminal on the switch will read zero with the switch turned on, and non-zero with it turned off - the non-zero value depending on the combination of load impedence and meter impedence(sensitivity) - regardless if it is a digital or analog meter, and if the nanalog is a symple d.arsenval movement or a VTVM. The reeding from LINE to NEUTRAL or GROUND will NOT show your phantom voltage, and the reading across the open switch is NOT phantom. As for meter connections, you NEVER connect a voltmeter in series with a load. You ALWAYS connect it ACROSS the load. The OP conected his/her meter IN SERIES with the load, so it was acting as an ameter but reading in volts, which didn't really mean anything (without knowing the exact sharacteristics of the meter in question) |
#23
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Fixed my porch light, not sure how
Sometimes, with no load, a digital meter will pick up a
"ghost load" reading. Or ghost voltage, can't remember. The two wires next to each other have a very slight transformer effect. Not enough to light a bulb, but enough to read with a DMM. Christopher A. Young Learn more about Jesus www.lds.org .. "TimR" wrote in message ... The back porch light stopped working, a new bulb didn't help. So. I put a meter on the socket. 0 V. I pulled the switch plate off (just a normal single pole). 80 V terminal to terminal. Hmmm? Killed the power, put an ohmeter terminal to terminal, infinite resistance at both switch positions. Diagnosis bad switch, supported by the fact that before it died completely, flipping the switch several times made it work. Besides I've always had a CFL in that one and I suspect the capacitor shortens the switch life due to arcing. Okay, a new switch is $1.29, no big loss if wrong. Took the old switch off, turned the power back on and checked wire to wire just for grins, still 80 V. Uh oh. Put the new switch in. Turned power on, checked the socket, 120 V. Put bulb in, (CFL), lights up fine. Well, I have a working porch light again, but I'm left with the 80 V mystery. I don't know any way to get 80 V on a normal residential power setup. The meter was a digital Radio Shack multimeter. If I'd had time I'd have checked again with the Simpson analog, digitals sometimes give funny readings, but I've never seen 80 V. What am I missing? |
#24
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Fixed my porch light, not sure how
On May 15, 7:21*pm, TimR wrote:
The back porch light stopped working, a new bulb didn't help. So. *I put a meter on the socket. *0 V. I pulled the switch plate off (just a normal single pole). *80 V terminal to terminal. *Hmmm? Killed the power, put an ohmeter terminal to terminal, infinite resistance at both switch positions. *Diagnosis bad switch, supported by the fact that before it died completely, flipping the switch several times made it work. *Besides I've always had a CFL in that one and I suspect the capacitor shortens the switch life due to arcing. Okay, a new switch is $1.29, no big loss if wrong. *Took the old switch off, turned the power back on and checked wire to wire just for grins, still 80 V. *Uh oh. Put the new switch in. *Turned power on, checked the socket, 120 V. Put bulb in, (CFL), lights up fine. Well, I have a working porch light again, but I'm left with the 80 V mystery. *I don't know any way to get 80 V on a normal residential power setup. *The meter was a digital Radio Shack multimeter. *If I'd had time I'd have checked again with the Simpson analog, digitals sometimes give funny readings, but I've never seen 80 V. *What am I missing? If you measured across the two wires that were connected to the switch, you're measuring the potential from hot *through the bulb* to neutral. If you want to sleep better, pull the switch off again and measure from hot to ground, you should then read 120V or thereabouts. If the bulb is a CFL there may be some odd effects causing an incorrect voltage reading the way you measured it. nate |
#25
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Fixed my porch light, not sure how
I started with the assumption the switch was bad, did the checking
mostly out of curiosity (and of course, when trying to figure out which breaker controls the circuit and the light is NOT working, it's handy to have a way to know). And yes I've had trouble with digital meters and phantom results on no load circuits, that's why I asked (and why I have a Simpson on the shelf, but unwinding all those probe wires is a pain, not as bad as winding them up to get them back in the case though). But on 120 V circuits normally that meter reads okay or floats a bit. I left out a couple of things. The fixture had no lamp in it, so that circuit should be open. The kitchen lights are on the same circuit, they went out when I got the right breaker (if I'd known that ahead of time I wouldn't need a meter, technically). The 80V terminal to terminal on the switch was with the switch off AND no lamp in the fixture. With switch on, it went to 0 as I'd expect. It was consistent with several measurements and was the same as wire to wire with the switch removed (and still no lamp in the fixture). That surprised me. And then when I went outside and put the same meter on the fixture and got 120 V I was suprised again. After work tonight I'll put the analog on it and see. |
#26
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Fixed my porch light, not sure how
"TimR" wrote in message ... The 80V terminal to terminal on the switch was with the switch off AND no lamp in the fixture. With switch on, it went to 0 as I'd expect. It was consistent with several measurements and was the same as wire to wire with the switch removed (and still no lamp in the fixture). That surprised me. And then when I went outside and put the same meter on the fixture and got 120 V I was suprised again. After work tonight I'll put the analog on it and see. One thing that you can also try with the analog is to set it to the highest voltage scale. If you show anything that is less than the next scale down, switch to that scale, the meter will stay almost the same physical place if a 'phantom voltage', you can then go to the next lower scale and the meter will not move much from the same physical point. The actual voltage the meter reads will be differant, but the physical point will not move much. This digital vers analog comes up almost as much as the WD-40 being oil or not. |
#27
Posted to alt.home.repair,sci.engr.lighting
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Fixed my porch light, not sure how
On Wed, 16 May 2012 08:19:29 -0700 (PDT), TimR
wrote: I started with the assumption the switch was bad, did the checking mostly out of curiosity (and of course, when trying to figure out which breaker controls the circuit and the light is NOT working, it's handy to have a way to know). Test the bad switch with an ohm meter And yes I've had trouble with digital meters and phantom results on no load circuits, that's why I asked (and why I have a Simpson on the shelf, but unwinding all those probe wires is a pain, not as bad as winding them up to get them back in the case though). But on 120 V circuits normally that meter reads okay or floats a bit. I left out a couple of things. The fixture had no lamp in it, so that circuit should be open. The kitchen lights are on the same circuit, they went out when I got the right breaker (if I'd known that ahead of time I wouldn't need a meter, technically). The 80V terminal to terminal on the switch was with the switch off AND no lamp in the fixture. With switch on, it went to 0 as I'd expect. It was consistent with several measurements and was the same as wire to wire with the switch removed (and still no lamp in the fixture). That surprised me. And then when I went outside and put the same meter on the fixture and got 120 V I was suprised again. After work tonight I'll put the analog on it and see. |
#28
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Fixed my porch light, not sure how
On Wed, 16 May 2012 12:35:14 -0400, Metspitzer
wrote: On Wed, 16 May 2012 08:19:29 -0700 (PDT), TimR wrote: I started with the assumption the switch was bad, did the checking mostly out of curiosity (and of course, when trying to figure out which breaker controls the circuit and the light is NOT working, it's handy to have a way to know). Test the bad switch with an ohm meter That works - but you need to turn the power off for that test. The voltmeter test requires removing the switch plate - and that is all -unless you can't get your test lead to the terminals without loosening the switch from the box - but the troubleshooting can all be done live. |
#29
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Fixed my porch light, not sure how
On May 16, 11:19*am, TimR wrote:
I started with the assumption the switch was bad, did the checking mostly out of curiosity (and of course, when trying to figure out which breaker controls the circuit and the light is NOT working, it's handy to have a way to know). And yes I've had trouble with digital meters and phantom results on no load circuits, that's why I asked (and why I have a Simpson on the shelf, but unwinding all those probe wires is a pain, not as bad as winding them up to get them back in the case though). But on 120 V circuits normally that meter reads okay or floats a bit. I left out a couple of things. *The fixture had no lamp in it, so that circuit should be open. *The kitchen lights are on the same circuit, they went out when I got the right breaker (if I'd known that ahead of time I wouldn't need a meter, technically). The 80V terminal to terminal on the switch was with the switch off AND no lamp in the fixture. *With switch on, it went to 0 as I'd expect. It was consistent with several measurements and was the same as wire to wire with the switch removed (and still no lamp in the fixture). That surprised me. *And then when I went outside and put the same meter on the fixture and got 120 V I was suprised again. After work tonight I'll put the analog on it and see. Well if the fixture had no lamp in it you should have read 0V no matter the position of the switch. The 80V you read was some kind of phantom voltage. nate |
#30
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Fixed my porch light, not sure how
Well, I tried again.
I actually do know how wiring normally works, but that doesn't prevent me from having a brain fart in the middle of a project. So, bulb (CFL) in, take some measurements off the two terminals of the switch. (note, neither switch nor box appears to be grounded; with switch off I can't pull any voltage from either terminal to box or ground screw on switch, and only two wires enter the box, both look to be #12 solid, one black and one white) Switch on. Both terminals should be at same potential, meters should read zero. Simpson 270 reads 0, R/S digital reads roughly 10 - 14, floats a bit. Switch off. One terminal should be hot, one terminal should be grounded through the lamp. Simpson reads 124, digital reads 121. Okay, now unscrew the bulb and repeat. Switch on, meters should read 0. Yup, both do. Switch off. What should they read? One is hot with respect to ground, but there is no ground in the box. The other is nothing, it is theoretically not grounded through the lamp but just a piece of metal in thin air. No current could flow, so intuitively the voltage difference should be zero, but I guess since we really don't know what potential that wire is sitting on it could be anything. R/S digital reads 84 V. Simpson reads 25 V. Which, if either, is real? The R/S will sometimes give me 10 V on just one probe, if the other is capacitatively coupled, but I've never seen phantom voltages off the analog. I guess the test would be to put a load on and see if I could draw a current, but I've spent enough time on this and there are other honeydoes to get to. |
#31
Posted to alt.home.repair,sci.engr.lighting
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Fixed my porch light, not sure how
On Wed, 16 May 2012 08:19:29 -0700 (PDT), TimR
wrote: I started with the assumption the switch was bad, did the checking mostly out of curiosity (and of course, when trying to figure out which breaker controls the circuit and the light is NOT working, it's handy to have a way to know). And yes I've had trouble with digital meters and phantom results on no load circuits, that's why I asked (and why I have a Simpson on the shelf, but unwinding all those probe wires is a pain, not as bad as winding them up to get them back in the case though). But on 120 V circuits normally that meter reads okay or floats a bit. I left out a couple of things. The fixture had no lamp in it, so that circuit should be open. The kitchen lights are on the same circuit, they went out when I got the right breaker (if I'd known that ahead of time I wouldn't need a meter, technically). The 80V terminal to terminal on the switch was with the switch off AND no lamp in the fixture. With switch on, it went to 0 as I'd expect. It was consistent with several measurements and was the same as wire to wire with the switch removed (and still no lamp in the fixture). That surprised me. And then when I went outside and put the same meter on the fixture and got 120 V I was suprised again. After work tonight I'll put the analog on it and see. OK - I read it that you checked the voltage at the socket and found zero, replaced the bulb and checked the voltage across the switch, which read 80 with the switch on and off - then you replaced the switch and got 80 and zero, and the light worked. If, as you state now, the 80 volts was with the bulb removed, capacitive coupling was giving you the 80 volts. (which happens not only with digital meters, but with "sensitive" analogs as well. You DO understand that you were not using the meter correctly? The CORRECT measurement is line to neutral - or in absense of an available neutral connection, line to ground. With a high impedence meter (like most digitals) you can substitute your damp finger for ground and usually end up within a couple of volts of accurate due to the high capacitance of your body coupling to ground (and NO danger of a shock). A good switch will read line votage on the line side, both on and off, and zero volts (or extremely close) on the load side with switch off and load connected, and line voltage with switch on - load or no load. I specify load connected on the OFF position because you can get those "phantom" voltages on a "disconnected" lead - which will dissapear if the wire is grounded through the load. |
#32
Posted to alt.home.repair,sci.engr.lighting
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Fixed my porch light, not sure how
On May 16, 11:40*pm, wrote:
*If, as you state now, the 80 volts was with the bulb removed, capacitive coupling was giving you the 80 volts. (which happens not only with digital meters, but with "sensitive" analogs as well. I'm following you, and agree, but with a caveat or two, because you're making assumptions that are not explicit. One is that there is no real voltage in the circuit. That is not a given. There can be sources connected accidentally that give real voltages between the 0 and 120 references. E.G., transformers for doorbells (it is at the back door), Another is, coupling to what? Hot is 120 referenced to neutral (there is no such thing as voltage, only voltage difference) but while ground SHOULD be the same as neutral, unless forced it may not be. The coupling can be to ground which may be at various potentials, or at some other object in the area - my aluminum screen door right next to it, etc. I didn't know analog meters could have that problem, I've always assumed when I was getting weird readings off a digital it was better to dig out the Simpson. And cart around ten pounds of meter instead of five ounces. Hee, hee. *You DO understand that you were not using the meter correctly? The CORRECT measurement is line to neutral - or in absense of an available neutral connection, line to ground. Well, yeah, I'll concede that one. When I opened the box I figured I'd check both sides of the switch to ground, and I'd find one leg hot and the other not, but of course there was no ground. And since you're supposed to switch only a hot, no neutral either. (I knew there was no power at the fixture, I wanted to check power to the switch, hoping I wouldn't have to trace back any further) I guess in hindsight I should have run a jumper to the nearest solid ground and checked that way instead. But it's not really correct to say I was using it as an ammeter. An ammeter measures current in a circuit. With the meter in series, that 10 million ohm resistance is effectively an open circuit, no current can flow. And with the bulb removed, the circuit should have been broken at an additional place. |
#33
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Fixed my porch light, not sure how
On May 17, 8:44*am, TimR wrote:
On May 16, 11:40*pm, wrote: *If, as you state now, the 80 volts was with the bulb removed, capacitive coupling was giving you the 80 volts. (which happens not only with digital meters, but with "sensitive" analogs as well. I'm following you, and agree, but with a caveat or two, because you're making assumptions that are not explicit. One is that there is no real voltage in the circuit. *That is not a given. *There can be sources connected accidentally that give real voltages between the 0 and 120 references. *E.G., transformers for doorbells (it is at the back door), Another is, coupling to what? *Hot is 120 referenced to neutral (there is no such thing as voltage, only voltage difference) but while ground SHOULD be the same as neutral, unless forced it may not be. *The coupling can be to ground which may be at various potentials, or at some other object in the area - my aluminum screen door right next to it, etc. I didn't know analog meters could have that problem, I've always assumed when I was getting weird readings off a digital it was better to dig out the Simpson. *And cart around ten pounds of meter instead of five ounces. *Hee, hee. *You DO understand that you were not using the meter correctly? The CORRECT measurement is line to neutral - or in absense of an available neutral connection, line to ground. Well, yeah, I'll concede that one. *When I opened the box I figured I'd check both sides of the switch to ground, and I'd find one leg hot and the other not, but of course there was no ground. *And since you're supposed to switch only a hot, no neutral either. * (I knew there was no power at the fixture, I wanted to check power to the switch, hoping I wouldn't have to trace back any further) *I guess in hindsight I should have run a jumper to the nearest solid ground and checked that way instead. You could have just used a jumper across the switch as a test and skipped all the meter drama. |
#34
Posted to alt.home.repair,sci.engr.lighting
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Fixed my porch light, not sure how
"TimR" wrote in message ... But it's not really correct to say I was using it as an ammeter. An ammeter measures current in a circuit. With the meter in series, that 10 million ohm resistance is effectively an open circuit, no current can flow. And with the bulb removed, the circuit should have been broken at an additional place. Actually in this case you are sort of using it as an ammeter when you put it in series with the circuit. That is why I mentioned the 'trick' with the Simpson of going down scale to see if the meter movement stays about the same physical place. The impedance of the circuit is high enough that you are getting an almost constant current of a few micro amps. There is really no such thing as a pure ammeter or voltmeter. It is just in how you are using it and how it is calibrated. If you look at most of the 'good quality' analog meters, they are using a meter movement of around 50 micro amps and resistors are switched in to make it show a full scale of whatever is desired. The Simpson has a meter movement of about 48 microamps (I think that is the number, or close) and one of the first calibration steps is to adjsut a pot inside the meter so it shows a full scale at 50 micro amps. I don't care to do the math right now, but you can calculate how much impedance it takes to have 10 or 20 micro amps and at what voltage. If you knew how long the wires are and a few things about the insulation, you could calculate the capacitance of the wiring and what voltage you should see. Just way too much to get into here. |
#35
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Fixed my porch light, not sure how
On Thu, 17 May 2012 05:44:59 -0700 (PDT), TimR
wrote: On May 16, 11:40Â*pm, wrote: Â*If, as you state now, the 80 volts was with the bulb removed, capacitive coupling was giving you the 80 volts. (which happens not only with digital meters, but with "sensitive" analogs as well. I'm following you, and agree, but with a caveat or two, because you're making assumptions that are not explicit. One is that there is no real voltage in the circuit. That is not a given. There can be sources connected accidentally that give real voltages between the 0 and 120 references. E.G., transformers for doorbells (it is at the back door), Another is, coupling to what? Hot is 120 referenced to neutral (there is no such thing as voltage, only voltage difference) but while ground SHOULD be the same as neutral, unless forced it may not be. The coupling can be to ground which may be at various potentials, or at some other object in the area - my aluminum screen door right next to it, etc. I didn't know analog meters could have that problem, I've always assumed when I was getting weird readings off a digital it was better to dig out the Simpson. And cart around ten pounds of meter instead of five ounces. Hee, hee. Â*You DO understand that you were not using the meter correctly? The CORRECT measurement is line to neutral - or in absense of an available neutral connection, line to ground. Well, yeah, I'll concede that one. When I opened the box I figured I'd check both sides of the switch to ground, and I'd find one leg hot and the other not, but of course there was no ground. And since you're supposed to switch only a hot, no neutral either. (I knew there was no power at the fixture, I wanted to check power to the switch, hoping I wouldn't have to trace back any further) I guess in hindsight I should have run a jumper to the nearest solid ground and checked that way instead. But it's not really correct to say I was using it as an ammeter. An ammeter measures current in a circuit. With the meter in series, that 10 million ohm resistance is effectively an open circuit, no current can flow. And with the bulb removed, the circuit should have been broken at an additional place. The meter WAS connected AS an ammeter. It was connected IN SERIES with the load. A voltmeter is connected ACROSS the load. |
#36
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Fixed my porch light, not sure how
On Tue, 15 May 2012 16:21:14 -0700 (PDT), TimR
wrote: The back porch light stopped working, a new bulb didn't help. So. I put a meter on the socket. 0 V. I pulled the switch plate off (just a normal single pole). 80 V terminal to terminal. Hmmm? Killed the power, put an ohmeter terminal to terminal, infinite resistance at both switch positions. Diagnosis bad switch, supported by the fact that before it died completely, flipping the switch several times made it work. Besides I've always had a CFL in that one and I suspect the capacitor shortens the switch life due to arcing. Okay, a new switch is $1.29, no big loss if wrong. Took the old switch off, turned the power back on and checked wire to wire just for grins, still 80 V. Uh oh. Put the new switch in. Turned power on, checked the socket, 120 V. Put bulb in, (CFL), lights up fine. Well, I have a working porch light again, but I'm left with the 80 V mystery. I don't know any way to get 80 V on a normal residential power setup. The meter was a digital Radio Shack multimeter. If I'd had time I'd have checked again with the Simpson analog, digitals sometimes give funny readings, but I've never seen 80 V. What am I missing? I didn't read all of the posts thoroughly, but I didn't see anyone mention the possibility that he measured 80 *milli*volts rather than 80 volts. If the meter is auto-ranging, that is a distinct possibility and often missed by those dambling in electrical work. The display says 80.0 and a tiny little mv is displayed on the side instead of V. Pat |
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