Over the past year we've noticed that we have lots of lights that burn
out, and more recently our smoke detectors (wired into house AC with 9V
battery backup) have had several batteries blowup. I just went around
the house and measured the voltage in outlets and found that some were
at 139 VAC, and some were at the normal 124 VAC. The power company
came and checked the voltage outside and said it's 124 VAC, and
suggested I may have a grounding or neutral problem.
How can I find the problem? Anyone know a really good electrician in
the DFW area (near the airport)?
Please email me at email@example.com
In my limited experience, if the neutral was lost at the panel or
upstream, causing the ground to carry the unbalanced current, the
voltage drops, not increases.
Isn't this house like violating some laws of physics?
tom @ www.CarFleaMarket.com
The ground won't carry anything unless there is a short.
The current has to be balanced; the exact same current goes out each hot.
Some voltages drop, some increase.
Assume you have a multiwire circuit with an open neutral.
There is nothing but a 50w bulb on circuit, and nothing but a 100w bulb on
The resistances are 288 and 144 respectively; with the neutral open the
total resistance is 432.
Since voltage is 240, current is 0.56a.
So, the 50w bulb sees 160v and the 100w bulb sees 80v.
I am ill with bronchitis, but this has to be close enough to give the
I was talking at the panel or upstream. Like the service enterence
cables are bad. There for phase a and b are still good, but
unbalanced loads are carred by the ground from the panel to ground.
Heavy resistance therefore voltage differential is decreased.
How to find a good contractor? Might as well ask why we are here. Can't
The utility's explanation is possible. Only problem is that in order to
have overvoltage in someplaces you must have undervoltage in others. Did
you find that? If not, then you don't have a loose neutral. With correct
circuits your 120v circuits are 120v hot to neutral. With a loose neutral,
you have no 120v circuits; they are all 240v, but half the circuits are in
series with the other half. If everything balanced it would not matter, as
all devices would see 120v. But it is rarely balanced. Then the two halves
see different voltages; if you see 139v on one circuit, you will see 110v on
another; and 170v on one and 70v on another. The math is very complicated,
but you get the idea. So, do you have some bulbs that aren't as bright as
they should be, or some outlets that read too low?
Reason I am suspicious is that, while it is not impossible for some the
circuits to have exactly the right voltage with a loose neutral, it is
unlikely. (Now it is possible to have a smaller problem, a loose neutral on
a multiwire circuit. Then only two circuits would be affected; one would be
overvoltage and its sister would see undervoltage, but you would still have
undervoltage. That is a much easier problem to fix, but from your
description you have a more extensive problem)
I hope either you or they checked both legs at the breaker box; they should
be 120v (plus or minus 5%). Don't measure at an outlet, measure from the
screws on a breaker to ground. If you aren't comfortable doing it, then you
shouldn't; but somebody has to. (It is exactly as dangerous as measuring at
an outlet, no more-no less, but it feels more dangerous.)
I'm not a licensed electrician but the above advice is very good and
correct. I had a similar problem in my last home. In fact, from time to time
the neutral would open and put 240 volts on part of the house. Now that will
end the life of your bulbs and wall warts quickly. I went to a junction box,
which was installed when the main panel was moved during and addition, and
found 4 neutrals twisted into one fried wire nut. I cleaned up the "not to
code" mess and called an electrician to bring it "all" back to code. I think
that is where you are at this point....that is, bring in an expert....good
I am a tad confused with your post.
You say 139 volts and also 124 volts. Measured how? with what? near the same
What you need is a recording volt meter. A strip chart meter for a week
would be nice, but probably the utility will not put one on unless you
"squeak really loud". A simple measurement at one point in time does not
tell you much of anything. (when looking at anomalies)
If your comfortable with playing about live wires, acquire an Fluke 87 and
place in on "record max voltage" run for 24 hours. then repeat on "min
voltage". This will tell you what the mins-maxes are, but not when. When is
the key, a lot of voltage anomalies are time of day related.
A loose neutral in your home will be hard pressed to create more voltage
that you start with on a 120v circuit. A loose ground on your serving
transformer is a different story.
IEEE 519 says that the utilities are supposed to maintain +10% to -5% of
The next paragraph says "except for short periods of time".
A loose neutral can mean one circuit will get up almost 240V.
In NA the power is supplied as 240 V It is divided into two 120V parts
for most uses. The three wires (plus ground) that come into your home
include the 240V (between the two hot wires) and the neutral wire which when
all the 120V loads are balanced carries no current. Without that neutral,
then 240 is applied to each pair of circuits. If one side has only a 10W
lamp and the other side has 10,000 watts of lamps that 10W lamp is going to
end up with almost 240V.
It sounds like they are right. A floating neutral problem (kind of like
a ground problem) is almost sure to be the problem.
You home is supplied with 240V AC not 120V. It splits the 240V (OK I
know this is a simplification but it works here.). It does this by using
the neutral (the third wire) to balance the voltage so when two circuits are
not using the same current they both still get 120V. When that neutral gets
loose or disconnected it means one half will bet something between 120 and
240V and the other will get between 0 and 120V depending on the load. Lower
load = higher voltage. The smoke detectors are low power users and are on
all the time, so if the other half of their circuit were to draw a lot of
current, the system would try to push all that same current back through the
smoke detectors by increasing the current up to 240V.
Most of the time the problem is at the circuit breaker box. In this
case you can be reasonable sure it is on the same circuit as the smoke
detectors. If you are comfortable working inside the breaker box and know
enough to keep yourself safe, (remember you can't turn off all the current
in that box) check all the connections of the white wires and the big wires
leading to the buss bars that the white wires are connected to.
If you are not comfortable with that idea, then call in the
professional. They should be able to take care of this is short order.
Don't leave it go, it can be dangerous and can damage electrical equipment.
BTW if you choose to do this yourself, and the above instructions don't
correct the problem. Call in the professional.
I am an electrician that does commercial and utility work. I am not,
however, in the DFW area.
You do need a real electrician there, it seems. If coworkers, friends or
family cannot recommend someone, I'd suggest you find a local electrical
supply house and ask the counter people there who they would recommend.
These people deal with electricians all day long... and they know the
knowledgeable ones and the dummies.
DO NOT open your breaker panel and start poking around, as it sounds like
you don't have the training or tools to be safe. While I usually respect Mr.
Meehan's comments, you should NOT attempt to tighten any "big wires" in the
panel. If they are feed lines, they will be live and touching them could
kill you unless you have properly insulated tools or pull the meter...
usually things only electricians have and do.
Cheap digital multimeters are not known for their accuracy, either. However,
a quick check (at the outlet) is to test the hot leg (the shorter of the two
prongs) and the ground prong to see if you get the same readings.
Please be safe!!!
This is Turtle.
WOW Jake , i was waiting for a Super revelation of a Diagnosis and was let down
by the reply you give. I will in the future have to just concider you as a Human
being and not a Super Electrical Sparky in the Ski. Now I do sometime have very
high expectation of people for I'm a optimist and not a Pissmorest. He He He 1
Well, T, you know the drill... the best answer is to keep Guy out of trouble
in this instance.
Neutral problems can come from anywhere. Doing utility work, we see it a lot
more in homes than we do on the poles or transformer interconnects, but that
No way to tell from here.
240 volt home service is made available phase-to-phase. The voltage
potential on each phase TO GROUND is always around 120 volts unless there is
a utility problem. Voltage potential on the Neutral, which should be
grounded at the service entrance (panel), can and does vary with the load.
At no load, there is no voltage potential. If someone reads potential from
Neutral to ground in a home, using a good meter, something is seriously
wrong and needs a professional to fix as soon as possible. Loaded, floating
neutrals are a fire and electrocution hazard, the second coming from how
many devices have the neutral improperly isolated from the ground and bad
equipment grounds on equipment and devices.
No Hot Shot opinion here... just the very good advice that Guy needs a good
electrician. I hope he finds one.
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