I noticed that some appliances were running better when plugged into certain
outlets. I am wondering what could cause the voltage difference. This is
in a room where the previous owner installed four GFCI outlets coming from a
dedicated subpanel. The measurements (with some loads still present) are:
134V outlet A
110V outlet B
113V outlet C
127V outlet D
I took off the face plates. The two pairs of outlets have a shared neutral,
i.e. one white wire comes down from the wall and goes into both outlets.
The other two wires in each outlet pair have the separate hots.. red wire
goes into the hot in one outlet and black wire goes into the hot in the
I also took off the subpanel cover. Here is a picture with the wires
clearly shown. It looks like each outlet has its own breaker:
The subpanel conduit goes all the way to the main service panel and I'm not
sure where it connects at the service panel. The house was built in 1950 so
the rest of the electrical is pretty old, but it this subpanel appears to be
independent of the old wiring.
I am wondering if it might be a mis-wiring at one of the outlets or
something simple that I can fix myself. I have done a lot of electrical
work at the previous house but I am not familiar with shared neutral
What if the main panel ground wire was reversed with the main panel neutral
wire at the subpanel? Would this cause the voltage behavior?
I noticed that the ground wire from the main panel is black (not green),
while the neutral wire is white. Could this have thrown off the installer?
A bad connection will cause a voltage drop when a current passes
through it. E=IR and all that. It applies not just to resistors and
intended loads, but to bad connections too. But that doesn't account
for the higher than expected voltage, and it seems liek it would take
3 bad connections, one for each of the lower voltages. That is, it
seems to me it doesn't matter if the loads on each outlet are
different. The voltage accross the receptacle should still be 117, or
close, and all the same.
Knowing these guys, I think they will tell you to make the
measurements again using an analog meter, although if by chance you
have an FET-VOM, since that has a verrry high input impedance, that
might not work.
Well, they always say that when a neutral or unconnected wire has a
substantial voltage, so maybe they'll say the same thing when a hot
wire has a higher than expected voltage.
It would certainly be using an analog meter to see if it reads the
same, or proportionate to a digital meter, which I have guessed that
Other than that, nothing in your story or picture seems to me to
account for the difference.
Originally I used a Kill-A-Watt device to measure.
I just tested again using a high end Fluke Multimeter. The outlet pairs now
show 125V, 118V across hot/neutral, but it changes slightly every time I
measure. In fact, now the high/low readings swapped sides within the pair.
I had also changed the location where appliances were plugged in to take
advantage of the high-performing outlets, so the difference in load might
have something to do with this swapping of the high/low readings.
Now I remember that whenever I have a high load on one outlet, one of the
other in the different pair suddenly performs better.. for example I plug in
the vacuum cleaner and then the aquarium lights get brighter..
Most of the time if you load one side of the wiring and the voltage on the
other side goes higher you have a neutral problem. Check at the braker box
where the power comes in and see if you get a change there of more than a
volt or two as you load the circuits. If so, it may be a problem with the
A house should be wired so the load is split between the two sides of the
wiring comming into a house. If the loads were ballanced exectually you
would not need the neuteral wire. This is almost an impossable situation.
The neutral carries the unballanced current. If there is a problem with the
neutral (open or bad connection) , one side of the wiring gets a larger
voltage and the othe side goes to a lower voltage depending on which is
loaded the most.
Indeed in the rest of the house, turnining on a load causes drops in voltage
in other completely different circuits. For example when I start the dryer,
which has its own 50A breaker from the main panel, this causes the computer
UPS to beep for a few seconds due to the drop in voltage. The computer is
on a different circuit with a 15A fuse in the main panel.
If this was a problem with the main panel, will the electric company come
out to fix it without charge? The panel looks pretty old, it might be the
original from 1950. How do these open or bad neutral connections occur? Is
it something like rust build up?
The power company is usually responsable for the wiring going to the power
meter. The home owner is responsable for everything past the meter. The
loose/bad connection can be anywhere from the transformer at the power pole
to the main braker/fuse box.
The connections can loosen up over the years. At every wire joint the wires
can loosen under the screws. I don;t really know the way this happens ,but
do know that it will.
You should get this looked into as soon as possiable . The lower voltages
are not to bad on things that do not have motors, but not good for motors.
The higher voltages, especially after you get over 125 to 130 will shorten
the life of many devices.
The power company does not handle problems AFTER the meter.
But I'd call them and have them check the transformer and wiring from
it to your meter. The transformer may be undersized or failing, or
some loose connections up there. If they dont find anything wrong,
its time for you to rewire or get an electrician. Wiring from 1950 is
probably fuses and it's time to upgrade. Of course it never hurts to
tighten all the screws in the box, and clean the contacts oon fuses.
The old cartridge fuses tend to corrode where they clip in the box.
Clean then with a wire brush or sandpaper, or just replace them and
see if that helps. Be sure your ground rod is still attached to the
wire that goes to the main panel. Sometimes they corrode off. Another
thing is to check all wirenut connections in boxes thruout the house,
especially those that are some of the main feeds from the main box.
In all fairness to Kill-A-Watt device, the voltage measures different at
different times due to the changing load that I put on the circuit. The
Fluke would measure the same, it's just that I did it during a different
time of day.
"mm" wrote in message
It certainly sounds like a floating neutral. This is a bad
connection(s) somewhere involving a neutral. It can be very dangerous. I
once worked for a photographer who burned down his first studio with that
Note: the voltages can change depending on the immediate loads on the
You don't have any aluminum wiring do you?
All of the wiring is copper. The other circuits besides this subpanel are
quite old. If there is one bad connection in the house involving neutral,
will it affect the entire house, even on other independent circuits coming
from the main panel?
For this type of set-up (Edison, I believe), the red and the black leads for
an outlet must go to a double breaker so that neither can be on independent
of the other. The breakers in the picture look like single breakers to me.
Check the voltage between neutral on the outlet and ground. I assume that
you have about240 VAC coming into your house. Note the sum of the voltages
on the outlet pairs is about 240. Thus the neutral must be significantly
different than ground. More than a few volts different at max load should
be indication of a problem. If equal sized loads are on the outlets then
there should be no current in the neutral lead and it should be at ground.
Indeed these are single breakers. The conduit from the main panel carries
four wires and 240V (this conduit originally went to a 240V receptacle). If
I have the breakers swapped out with double breakers will it help the
symptoms or is that more to do with the NEC code?
I measured the voltage between neutral and ground, with loads still plugged
in. When I place the Fluke lead into the ground hole touching the exact
same position where I measure 110-130V between hot and ground, there is only
a 0.1-0.2 voltage different between neutral and ground. If I move the lead
in the ground hole so it touches some other part of the metal inside, I get
a consistent 7-9V difference between neutral and ground. That is strange, I
thought the ground contacts inside the outlet are all the same piece of
metal. These are new Leviton GFCI outlets.
Circuits on the same hot leg should not be sharing a netural. You have
tandem breakers (which are on the same phase or hot leg) which are sharing a
Shared netruals are OK in a multi-wire curcuit, which uses both hot legs
(one for each 120V circuit) and share a neutral.
Get them split up and off the same hot leg.
From all your described symptoms, there is no doubt that you have a poor
connection somewhere in the neutral line. It can be anywhere from the power
pole, down thru the meter socket, and into the main and sub panels. To
determine where the problem is, you have to see how far back toward the pole
the problem shows up. Each side of the system should have approximately the
same voltage to the neutral and the neutral to ground voltage should be near
zero. A few volts of difference is not significant but as much as 5 is not
This is a serious problem and if you do not feel competent to solve it you
should seek help from someone with more experience.
This is interesting: I just measured a 3 to 4V difference between the
service panel ground wire connected to the pipe, and a nearby fence post.
The yard also has a new water system so all of the metal pipe was replace
with PVC before we moved in. So the pipe will not be as effective as a real
ground stake. As a test I ran a temporary green wire between the ground and
the fence post. This reduced the voltage discrepancy in the outlets also by
around 4V. However the loads in the circuit are constantly changing so I
cannot be certain it was due to this fence post wire test. With some heavy
duty stakes in the ground I'm wondering if that will make up the 10V
discrepancy (and not just 4V). I will have this ground stake re-done for
sure. I wonder if this is it, or something else too.
Measuring to various grounds may help you understand and diagnose the
problem, but the problem itself has nothing to do with grounds. It is a
neutral problem and you need to understand the difference to understand the
problem. A good low resistance neutral from the pole transformer to the
breaker box(es) is what maintains the system voltages balanced with varying
loads. The ground(s) will somewhat do the job if the neutral has a high
resistance and is therefore not doing the job properly. But your problem is
with the neutral and not the grounds. Just find the loose or corroded
connection if it is in the breaker boxes or call the power company if it is
in the meter socket, in the drop cable, or at the pole.
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