Low Voltage Problem

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  #1  
Old 03-27-02, 02:03 AM
Debbie Ann
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Question Low Voltage Problem

What could cause a fixture and a switch to measure low voltage? A lot of work has been going on in this old apartment, so something has happened to cause this. I do know the light fixture and switch worked prior to the work being done.
 
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  #2  
Old 03-27-02, 11:55 AM
Wgoodrich
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You really need to be more specific as to what you are calling low voltage. How much voltage are you reading?

If you have had work in your area it can be a small as a wire that didn't get under a wire nut that had been replaced to a grounded leg or neutral being cut. Right now with what you told us it is wide open for guessing.

Wg
 
  #3  
Old 03-27-02, 07:25 PM
Debbie Ann
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Hi Wg...
Sorry about that, I know I should have given you more info....The voltage I'm getting is 30 volts. The fixture and switch read almost the same, I have the analog type meter, and I checked other outlets to be sure the meter is working properly. I'm definiately going to buy a digital meter, the analog is dificult to work with and it is hard for me to read an exact number. Can you also tell me a good digital meter I can buy at Home Depot? Thanks.....
 
  #4  
Old 03-27-02, 08:43 PM
DaveB.inVa
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Just a note that a digital meter is a high impedance device. This means that even the smallest current (and I mean small) will cause the meter to read almost full voltage even when there is no real voltage there!! For example I have a fieldpiece digital meter and If I remove the bulb from a circuit with the switch off this means that the wire is not connected in any way to any electrical source. I can read almost 100 volts to ground just because the wire being insulated from an electrical source acts like a capacitor. This small capacitor is now discharging through my meter and showing me 100 volts. That 100 volts is in effect not really there, it doesnt have the power to drive any load. Lots of analog meters will produce this same effect, but to a lesser degree.

Dont get me wrong, digital meters and analog meters do have their respective places. But the best meter you can ever really get would be a solenoidal meter like Square D's Wiggy!! (about $20) They only will give you a rough estimation of your voltage (nowhere near as accurate as an analog or digital meter) but the Wiggy surely will never lie to you!!
 
  #5  
Old 03-28-02, 10:45 AM
Debbie Ann
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I thought a digital meter would be better. It seems that I've heard that on this forum, but I could be wrong. Could someone give me another opinion? Thanks
 
  #6  
Old 03-28-02, 11:30 AM
jlbos83
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First, I think that for this purpose there really isn't any benefit to a digital meter over the analog you are using. An exact number isn't what you are after, really.

Now, on to the 30V. What is the 30V with reference to? Was that neutral to hot, ground to hot, ground to neutral, or what? I assume that that measurement was made with the switch on, and no device in the fixture? I am guessing that there is no power to the switch. The thirty volts is pretty much an arbitrary reading for an open circuit, I expect. If you put a bulb in the fixture, what does the voltage read? I just sounds like an open to me. There really are not very many ways to get a low voltage especially with no load.

My opinion is that a careful inspection of the whole circuit, particularly ahead of the switch will be alot more productive that worrying about what meter to use.
 
  #7  
Old 03-28-02, 10:31 PM
Debbie Ann
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My readings are as follows:
Fixture =
Hot to Neutral = 30 V
Hot to ground = 120V
Neutral to ground = 5V

Switch = only 2 old braided wires coming into metal box no switch attached, wires are not connected to anything. I looked at the wrong notes when I asked my orginal question. I do have the following readings.
Switch =
Hot to Neutral = 10 V
Hot to Ground = 20 V
Neutral to ground = 0 V

I will inspect the entire circuit.
Don't worry jlbs83, I am not more worried about which meter to use..just asking an opinion on what digital meter is a good one. LOL
 
  #8  
Old 03-29-02, 04:01 AM
B
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Radio shack for multimeter

Radio Shack and Sears also carry multimeters.
I don't know what DaveB uses, but my VOM (volt-ohm meter) has been very reliable. The key is selecting the correct range and plugging the leads into the correct spot on the meter.
 
  #9  
Old 03-29-02, 07:18 AM
Debbie Ann
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Thanks Bob...
I thought there is a good digital meter out there.....


Do you know anything about my low voltage readings/problem?? I sure would like to know what could be wrong...
 
  #10  
Old 03-30-02, 08:46 AM
jlbos83
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There are lots of digital meters about, and they will all do what you want, probably. If you are going to use it a lot, the Fluke meters are good , sort of industrial grade meters. They will take a lot of abuse. If you are wanting to measure current, you might want to get an inductive probe, or a clamp on meter. these let you measure the current without breaking the circuit, it can be handy. My point was that for what you are doing, the analog meter is fine. You can read the meter plenty accurately enough for this job. Sometimes an analog meter is better, since you can see changes as they happen, rather than as the digital meter averages them to display.

As to your problem, your measurements make these suggestions to me. It sounds like the neutral is open, since you have 120 hot to ground. Which side of the switch were you measuring. Since there wasn't 120 anywhere there, it sounds like you were on the 'controlled' side of the switch with the switch off.

Something to remember, when you have an open, the voltage is pretty much indeterminate, so the 10, 20 and 30 probably don't mean much. I would be looking real carefully at the neutral line.
 
  #11  
Old 03-30-02, 11:11 AM
Debbie Ann
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Hi jl.

As I mentioned in my earlier post, there is no switch. I only measured the 2 old braided wires the same as I measured the fixture wires. Thanks for the advice about the open neutral. I will check that out.
What do you think could be the problem regarding the measurments I'm getting at the box that also has only 2 old braided wires? That is the switch box that controls the fixture.
Thanks
 
  #12  
Old 03-30-02, 11:26 AM
zekester
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The answer given to you about the meters are correct. You don't need it. A high impedance digital meter is a must in automotive work. Maybe that's where you got the idea.
 
  #13  
Old 03-30-02, 11:28 AM
jlbos83
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OK, I need to get my head around a picture of what is here.
Follow me and fix if needed-
There is a box, where a switch would be. There are two wires in the box. Question...is that two wires, or two cables, with several wires in each. How are you determining what wire is hot, neutral and ground? Where do the sires, or cables at this box come from, or go to (at least what you know about)?

Here is what I am thinking:
Power is coming to the fixture in a two wire cable (or as two wires). One of these is hooked to the fixture, the other just goes on to the switch, in another two wire cable (or two wires). The second of these two wire is hooked to the other side of the fixture.

If this is the case, everything may be fine, one you have a switch. You already have 120V in the fixture, that says power gets that far. You would never have any voltage at the switch, it is just opening the hot. There is no neutral for reference (and in this old thing, maybe no ground? Experts on old stuff, HELP!) Then the switched power goes back to the fixture, but if the switch is not there, no power is ever at the fixture.

I think we may actually be getting closer to figuring out what you have.
 
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