Fixed my porch light, not sure how

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.

Reply to
Ralph Mowery
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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?

Reply to
trader4

Test the bad switch with an ohm meter

Reply to
Metspitzer

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.

Reply to
Ralph Mowery

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.

Reply to
trader4

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:

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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.

Reply to
bud--

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.

Reply to
TimR

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.

Reply to
clare

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)

Reply to
clare

Except the OP had a CFL in the socket when they tested the voltage across the switch.

Because the meter was, as I said, misconnected for the rquired test.

Reply to
clare

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.

Reply to
clare

Correct.

Reply to
clare

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.

Reply to
clare

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.

Reply to
clare

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)

Reply to
clare

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

Reply to
Pat

Again I ask, in a slightly different form, what, in your expert opinion, is the proper way to connect two probes to two wires?

Reply to
HeyBub

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.

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.
Reply to
TimR

You could have just used a jumper across the switch as a test and skipped all the meter drama.

Reply to
trader4

I read the original post as not having any bulb in the socket. From the OP's post yesterday that is correct.

Bullcrap. There is nothing wrong with measuring the voltage across the switch if there is an incandescent lamp in the socket.

From the OP's post yesterday there is no neutral or ground at the switch. It makes even more sense to measure the voltage across the switch (with a lamp). Repeating Hey's question - how do you connect two probes to two wires, no ground, no neutral.

I have, for instance, measured the voltage across cartridge fuses. If there is voltage the fuse is open. If there is no voltage further checks are required. (But then the US does not have fuses that "weld themselves back together and work for a while".)

Reply to
bud--

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