Fixed my porch light, not sure how

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On 5/18/2012 2:15 PM, snipped-for-privacy@snyder.on.ca wrote:

Forget it clare. I have been a licensed master electrician for about 40 years and do this diagnostic stuff a lot.
Still missing - an answer to Hey's question. Two wires, no ground, no neutral.
--
bud--

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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.
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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.
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wrote:

Well if you don't like using ground and a neutral is no good because you have to take off a wire nut, how would you propose to do the test?
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Often in a light switch there is no neutral to have a wire nut to take off.
If there is no neutral or I suspect the ground is not connected, I use what some may call a 'hot stick'. It is a device about the size of a cigar that lights up and/or beebs when held next to a wire that has voltage on it. Cutting the breaker off and on while using the hot stick usually confirms there is power or no power at the switch. Then with the power off, I check the switch using the ohms fuction.
I often use a Simpson 260 because I do not like the digital meters for general testing due to the 'phantom' voltages. Another favorite is a Fluke T2. I think that is the number. It has about 10 LEDs in it. It will check from about 6 volts to 600 volts AC/DC and also low resistances. Just hook up the test leads and it will show if you have power or a short.
I do admitt that I have several differant testers that most home owners do not normally have or really need. I also have a Fluke 87 digital meter, but seldom use it for electrical test due to the 'phantom ' voltages. I work in industry where I have to deal with anything from low voltage control and instruments to 480 volt 3 phase circuits. That is the reason for having those plus several other testing devices.
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Round these parts, the vast majority of them do have neutrals. Usually the power feeds from the panel to the switch via a romex that has both conductors. Current NEC code now requires that they have neutrals.
But that is why I said to just test it by holding one lead to ground. And again, around here the vast majority have grounds.


Yes, he could use one of those if he happened to have it.

Agree, he could do that too.

The phantom voltage issue is more of a problem of people having a lack of understanding of circuit fundamentals. The OP's test procedure being an example. I don't think either of us would have tested it the way he did. If you understand how circuits work, it may cause you to do a second test, etc, but it's not really confusing.
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On 5/16/2012 11:33 AM, snipped-for-privacy@optonline.net wrote:

I thought having many test devices was about having the most toys when you die...
I am a lot more paranoid about possible failures and arc flash after seeing some videos. Measuring on high capacity circuits, the meters should be "category" rated. OSHA is likely to take a dim view of using not-cat rated meters on high capacity circuits, particularly if there is an injury. Fluke is likely to be cat rated. Not sure any Simpson 260s are. Digital is also nice because it is more compact. (I coveted a 260 when I was about jr high school and finally got one at a garage sale recently.)
If using a Fluke, or similar, you can substantially eliminate phantom voltage with an accessory: http://www.fluke.com/Fluke/usen/Accessories/Batteries,-Chargers-and-Adapters/SV225.htm?PIDV696

On the other hand, the test would have been fine if there was an incandescent light bulb in the socket.
I agree about circuit fundamentals, and part of that is understanding the limitations of measuring tools (like phantom voltage).
I remember the first time I saw the effect described by Ralph where the voltage reads about the same point on the scale on different analog ranges. I figured it out pretty fast, but it is weird.
--
bud--

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On 5/16/2012 1:12 PM, Ralph Mowery wrote:

One of the smartest electricians I know wanted to measure the current for a motor in a food processing plant. It was a possibly explosive atmosphere so there was a motor control center in a purged room. He defeated the interlock on the module door and amp-clamped a motor wire - an absolutely standard procedure. No one knows what happened - maybe a loose screw faulted the busbars, but there was an arc flash. He was badly injured (including condensed copper on him) and was in the hospital quite a while. The facility was buying distribution voltage power from the utility and one of the fuse holders was destroyed in the event - I have no idea how that could happen. (Arc flash was not an issue back then.)
At a trade show a manufacturer field engineer had a seminar. As an aside, he was working for a major company like Westinghouse and the client wanted a module for a motor control center or switchgear. The space was open so he was measuring the size with a steel tape. The next thing he knew he was on his back on the other side of the room. If he hadn't been thrown he might be dead. At least in that case he did something dumb.
Some of the required inservice classes have covered arc flash. They had an arcflash suit - pants, top, hood and gloves. (And the protection includes the natural fiber clothes inside.) Don't know how you do useful work in something like that. Someone brought in copies of the labels at his facility that are required to evaluate what protection is required. One of them said something like "No safe approach is possible" (with protective panels removed).
The default standard for worker electrical safety is NFPA 70E. Your plant must have a copy and I wouldn't be surprised if you have read it. Interesting information on what protection is required for different voltages and available fault currents.
--
bud--



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I just retired as of yesterday. We have all the protective gear. Gloves, coat, face shield. While we seldom use it, we have a couple of special outfits that are rated for 100 cal. The coats we normally have are rated for 40 cal. I was almost tempted to bring my 40 caliber Glock on the last day and shoot at my arc flash coat and tell them it would not protect against a 40 caliber... Almost impossiable to do useful work with that junk on. Most of the time we can cut the power off and do a test and then take all the stuff off.
We have lables like that all over the plant. It is a large plant and covers many acers. A small building ( maybe 50 x 100 feet) has a motor control center and it had a sign on it that mainly stated we could not get within about 500 feet of it. That ment if any breaker on it tripped, it would have to stay off. Someone finally wised up and replaced that sign with one that was workable.
Most of the arc flash junk started when a company came up with some high dollar main breakers that were suspose to trip under certain conditions. As many companies did not want to replace them, the arc flash hazard was 'invented'.
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wrote:

At his day job, one of the instructors of our nightly apprentice program at the International Brotherhood of Electrical Workers put a wiggy on the line terminals of a 4160V switch gear once. As a reminder, a wiggy is good for 600V.
This did not end well. I don't remember the details, but I have heard the story a thousand different times. /////// When I was an apprentice, my roommate was also an apprentice. He worked for a very small company. The company was dad, son and my roommate. The son was changing a buss fuse under load. When the two maintenance workers that were in the area because of the outage became aware of what the son was doing, they ran for the door. I am told that both maintenance workers were burned on their back half of each's bodies as they had made it to the door and were each half shielded by the door jam as they left the room. The son was killed. He was an experienced electrician. The rush to restore power to the building cause him to make the error. http://en.wikipedia.org/wiki/Peachtree_25th_Building
* wiggy = voltage tester (solenoid)
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On Wed, 16 May 2012 13:00:35 -0400, "Ralph Mowery"

The simple old neon tester is still the simplest troubleshooter for domestic wiring - the old solenoid tester to determine what line voltage you are working with (usually 24 to 600)
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On Wed, 16 May 2012 11:57:44 -0400, "Ralph Mowery"

In which case you will still have a "capacitive ground" which will give an (inaccurate but more or less consistent) reading. The test will still tell you if the switch is working or not. A simple neon tester will do the same, using your pinkie as ground.
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On Wed, 16 May 2012 08:31:57 -0700 (PDT), " snipped-for-privacy@optonline.net"

Correct.
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wrote:

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.
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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.
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snipped-for-privacy@snyder.on.ca wrote:

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.
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wrote:

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)
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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 .
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?
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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
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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.
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