Home electrical question

eyeeatingfish

eyeeatingfish

Joined
Dec 9, 2003
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I have a home electrical question for any electrically savvy people here.

So my 4 bulb fluorescent light fixture (only had 3 bulbs) inside my kitchen went out. I went to the hardware store looking for ballast and the guy suggested testing the wires first, so I went back home, pulled out my multimeter, and read 120 volts at the black and white wires coming out of the ceiling. So I went back and purchased the ballast and the light works again.

So here is the potential problem. I had turned the circuit breakers off while disconnecting the wires for safety. Well when it came time to put on the ballast I was thinking to myself what if I just turned the switch off instead of the breakers? That way I wouldn't have to spend time walking back and forth. So to see if it was safe I left the breakers on and the light switch off. I then tested the wires again with my multimeter. I was surprised to see a reading of about 40 volts. When the breaker is off then the wires read 0.
So I am wondering why, if the switch is off, is there any voltage going through the lines? Furthermore if something was broken and allowing voltage to go through the lines why is it only letting 40 volts instead of 120 volts? And lastly does this mean that I am wasting electricity, is there juice flowing through the lines and being used by the light fixture even when the light switch is off which I am having to pay for?
I was thinking I could at least try to change the switch but I am not sure if the problem is that simple.

Oh to clarify I live in a concrete condo for the last 2 years, and hadn't done anything construction wise involving that light or wires other than install track lighting in a nearby room.

I have a multimeter from batteryjunction similar to this one. It has lots of settings that I don't fully understand but I am pretty sure I got the setting on AC voltage. I don't know which place the decimal was in but I figure I should still be able to understand the reading. I left it on the same setting both times i tested the wires.
http://www.batteryjunction.com/a-dt-9205a.html

A preemptive thank you for all that provide advice.
 
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i don't know why there is a discrepancy with the voltage.
But -if if you leave your circuit live and have the light switch off and then start touching the wires in the light fitting- pretty sure at some point you will complete the circuit and it will hurt you.
I know because i've done it OK.
I have also witnessed an electrician work on the lights while power was on with no ill effect.
I now have earth leakage circuit breakers installed in the new fuse box so should be safe if i drop the toaster in the bath.
but don't take my word for it -i'm not a licensed electrician.
 
did you see any lines going out of the box besides the ones going in to power your light? some electricians use travelers as in two wires in one out and then take that one to the next light and then connect the next light over to a switch and ground so that second light can have power. instead of running two full sets of cabling... im not an electrician but my dad is and hes shown me somethings over the years
 
Well i used to be an electrician and i can mostly answer your question. First off assuming you only have one live or powered wire coming in if you turn the light switch off you should be fine without having to turn the breaker off. Just check and double check before you barehand any wires just to be certain. As for the possible power trickle thats hard to explain if the light switch is a dimmer it will leak small amounts of voltage constantly. But since you said you turned the breaker off there shouldnt be anything at all. So either it was the wrong breaker or there is another circuit in that fixture. It is hard to give a for sure answer on this type of thing without actually seeing it, but those are the only possibilities i can think of.
 
Sorry I should clarify, the lines did read 0 when the breakers were off so I know the breakers work fine. The light switch is not a dimmer, simple on and off, the kind with the big wide button, not the skinny knob that goes up and down.

The way the building is, in most of the rooms the switch operates an outlet for a lamp or something. The exception is the bathroom, kitchen and living room. The living room light and bathroom light boxes are both at least 10 feet away from the kitchen light box. Coming out there was one black, one white, and one ground. I did not get a good look inside the box as it was partially covered by the light fixture that has a smaller hole for the wiring to come down from.
I do think that when I installed my track lighting i saw wiring in the box that did not appear to be part of that fixture, kind of like it was traveling through or something. I can check that one easily but the kitchen one would be a bit more work. There are not any other lights or functions on the kitchen light switch but I don't know whether the wiring could be tied into something else. I can try to get a better look at what wires are in the box and maybe even take a picture.

Does that help?
 
Three questions:

1) Is there anything else on the circuit after the switch, i.e. that is also controlled by the switch? Another light fixture? An outlet?

2) When you made your mysterious 40V reading, was the old ballast still attached?

3) Is there anything else on the circuit before the switch, i.e. that is controlled by the breaker, but not the switch?
 
If it's an older house, sometime they used to "switch" the neutral wire (white) instead of the hot(black) wire. That would explain your reading.

Basically the black wire is still "hot" and there is no neutral (return) at your light fixture when you shut the switch off.

A lot of the old 'knob and tube' wiring is that way.

BTW, I'm an electrical contractor.
 
Basically the black wire is still "hot" and there is no neutral (return) at your light fixture when you shut the switch off.
Click to expand...
Then wouldn't the hot wire be at full voltage? He only found 40 volts. :confused:
 
The hot would be at full potential, yes. But the neutral would be floating. Well, nothing really floats. It has some capacitance to ground and that's why you would see some potential.

But the impedance of that potential is very high. There is a potential voltage, but no potential current. A digital volt meter will measure it. An analog meter won't. And a test light certainly would not.
 
I am a residential (mainly) electrician.
I have seen some things similiar to this before. Often it can be related to poor grounding in the home.
I wouldn't worry about it costing you any money.
With things like these sometimes one tester would show voltage and not the other like Gollnick said.
 
Like the two previous posters said, on all likelihood you have a condition known as a floating neutral (the white wire is the neutral and the black wire is the hot)... it's fairly common issue with older homes. Basically it is caused by a lack of having your electrical system properly grounded. You can check to see if you have a floating neutral by doing a continuity test between the neutral bus (where all the white wires are connected/terminated) and the metal enclosure of the equipment containing the breakers (electrical panel). If you get an infinity reading (open line), this indicates a floating neutral condition. While having a floating neutral is typically not a dangerous situation, you can experience a shock if you touch the white wires and are also grounded at the same time.

YMMV,
dusty
 
I live in Hawaii, the building was built in 1978.
The ballast was not connected when I was doing my tests.
There is nothing else activated by the same switch as far as I can tell.
There are other lights that are controlled by the same breaker I believe. The breaker box is not really well labeled so I am not sure exactly what but I do believe the living room lighting, the bathroom lighting, and maybe the hallway light is on the same breaker.

I have the push button breakers not the newer switch style.

Dustyzz: what is an infinity reading on my multimeter?

So if I understand this floating thing the neutral wire somehow has some voltage running through it? And if I test from the neutral to the ground, or the electrical box, it might give the same reading of 40 volts? If so is this something to fix?

Or as varg suggested the hot wire is still pumping electricity through but because the neutral is switched off the resistance is increased but is still letting some electricity go through the lines? But if the hot wire is sending electricity through then is must have somewhere to go right, and this means the neutral is somehow grounded? Would this be wasting electricity?

Could this be damaging my electronic ballast by putting some voltage in the wrong way when the light is off?

Thanks for all the suggestions so far.
 
Nailsinmynose said:
did you see any lines going out of the box besides the ones going in to power your light? some electricians use travelers as in two wires in one out and then take that one to the next light and then connect the next light over to a switch and ground so that second light can have power. instead of running two full sets of cabling... im not an electrician but my dad is and hes shown me somethings over the years
Click to expand...

yes lesson learned -my house has what we call "loop in wiring" for the light circuit. now at least i know how i got zapped.I promise it won't happen again.
 
eyeeatingfish said:
I live in Hawaii, the building was built in 1978.
Click to expand...

I don't know about Hawaii, but I believe that the National Electric Code allowed two circuits in one box at that time. I'm not sure if switched-neutrals were out by then, but I'm pretty sure they were.



The ballast was not connected when I was doing my tests.
There is nothing else activated by the same switch as far as I can tell.
Click to expand...


What I was looking for in these questions was a X capacitor. A lot of devices have a small capacitor between hot and neutral which is there to filter out radio noise. It can store a small charge which can appear as a voltage. But, that is not the case here because there is no other device.


There are other lights that are controlled by the same breaker I believe.
Click to expand...

This just means that the neutral is long.

What you have, I suspect, is what is called a "Phantom voltage." It is caused by capacitive coupling between the wires. You would not have seen it had you not been using a digital meter. Because it is very high impedance, it is not a concern. If you tried to draw a current from it, it would disappear.

I do suggest that you check your neutral/ground bond. At Home Depot, you can get a little tester that plugs into a three-wire outlet and has three lights. When plugged into a properly-wired outlet, two will light. There's a little chart printed on the thing that decodes what the pattern of lights you see means. This thing costs maybe $10.

Testing the actual ground requires an instrument that costs upwards of $1000 and it's a technical and somewhat dangerous test best left to a qualified electrician.
 
Two hots (two circuits) on a single neutral. If you turn off one circuit, you can get some back feed through the neutral from the other hot. Seen it lots of times. (felt it a couple of times, too.)
 
Ok, so the neutral line is somehow storing a small amount of voltage somehow, but even though the voltage is higher there is not much power to it? (like how a dead battery can read 1.5 volts on a multimeter but when something tries to draw on it there is no power.)

When I can find time to go and test the neutral to ground with the multimeter I will post what the result is.

As for the infinity reading that is between the neutral and the ground? And am I supposed to test the voltage, see if there is a completion of a circuit or test the resistance?
 
Multimeters can be inaccurate. I had an older analog one that was more like a light probe then a multimeter.

Regarding residual voltage, think of it as residual capcitance unless you are getting actual current flow (AMPs). You probably have a floating ground but, you could have a poor "house" ground as mentioned above. Essentailly, your wire is probably storing a little charge similar to how a battery would and shouldn't be running up the electric bill.
 
A couple of thoughts. Back in 1978, they generally used the steel conduit as a ground path. Thirty years of humidity, salt air and direct contact with concrete can rust through that conduit, leaving it ungrounded. That can cause some potential between neutral and "ground". As someone else said, having another load running on the circuit could cause voltage to show between neutral and ground. And one more possibility is induction voltage. A conductor carrying current will be surrounded by a magnetic field. If another conductor runs parallel to it within that magnetic field, the field can induce voltage in the second conductor. So if wires from two different circuits are run in the same conduit, you may see some voltage on wires of one circuit even with the breaker for that circuit turned off if there is a load running on the other circuit.
 
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