I realize this is a topic covered rather regularly but my problem
doesn't seem to be solved and I'm hoping for new directions.
My house was completed in 2003, i have a substantial light diming
problem that i have had since the house was completed, and investigated
to no avail. While some people say dimming is "normal", ours seems to
be quite dramatic to the point where guests ask "what was that"..The
builder's electrian claims there is nothing wrong, we had the utility
company out and the put their "beast of burden" on the lines and said
the voltage drops were from 121 down to 117 on both lines. We are the
only house on the transformer ( which looks old to me)and the house is
about 250 feet from the pole (underground service)..We subseqently
hired a second electricain who spent five hours trouble shooting,
checking the main panel connections, checking to see if moving breakers
would help without any luck. We did discover a overloaded kitchen light
circuit and the Ac units wired with 10ga wire with 50amp breakers...
I need help...I realize a small flucs in the lighting could be
normal..but this seems to be substantial...we are considering
purchasing a hot tub..but with the dimming I'm not sure it is wise..
Anyone got anything new ...Any ideas?
You need to monitor voltage to see what it is. Hobo might make a cheap
voltage recorder to hook to your computer. Without knowing what the drop
and duration are you will have trouble finding it. Even now having a
volt meter where you can see a drops voltage would help. You might
contact an electric supply store they might stock a meter that can store
data. Google Voltage Recorder. Just because the electric company did not
see their equipment as bad, it could be.
Is the dimming momentary or for an extended time? Usually momentary is due
to something like a heat pump or air conditioner starting. An extended
dimming could be due an electric water heater or some other large electric
what lights are dimming? the last few volts make up a large amount of a
lamps brightness. is it worse at some times than others?
you should get a recording volt meter and check the line condition over
a period of days,
might be a heavy occasional load on the service line in your area,
may just be cheap ligts or fixtures.
I used to fix copiers and this came up with certain customers and our
own office. When heavy loads were on the voltage would sag, dimming the
exposure lamp making for too dark copies
The note about the A/C wired with #10 and 50A breakers is troubling, but
the source of your dimming is probably the extremely long run to the
transformer on the pole. You indicate 250' to the pole, then you add in
30' up the pole and another 10' into the house and you've got near 300'
of service drop. If the drop cable is not significantly oversized you
will get a sizable voltage drop under load.
I don't know how much load was on the line when the utility indicated a
drop to 117V, but that is a fairly large drop. It's also conveniently to
the minimum voltage that is generally considered acceptable for the
utility to supply. Add voltage drop within the house and you can
certainly get a noticeable reduction.
There are not many easy solutions to this problem. You can get an
independent electrician to test and if they can show the voltage to your
panel drops below 117V under load you may be able to force the utility
to upgrade your feeder. This depends a lot on what state your in and how
good your states utility control commission is.
Outside of upgrading the service drop there are not a lot of good
solutions. The voltage drop may be annoying, but it's not really
problematic electrically. You could install a sub panel to handle the
lighting and general use circuits in the house and keep all the heavy
loads like A/C, dryers, ranges, etc. on the main panel.
Installing a line conditioner on the feeder to the sub panel would
control the voltage drop to the sub panel which would have the circuits
where you would notice it. This would not be inexpensive, but it would
likely be less expensive than the cost of upgrading a 300' underground
utility feeder if you had to pay for it.
You can also try experimenting with different types of lighting such as
compact fluorescent which might not show the voltage drop as much as an
Thanks for the info..just out of curosity..who is responsible for the
proper sizing of the feeder, the builder or the utility company?...If
we install a hot tub ....I realize that the pumps and heaters will draw
a load..in turn more dimming..the service to the house is 200amps..am i
then going to be looking at having to upgrade the feeder?
In the areas that I am familiar with the utility is responsible for
everything up to the meter socket and for the voltage delivered at that
point. They are normally well aware of voltage drop issues on very long
service drops like your 300' so they would usually get it right.
Anything over 100' is typically considered a long drop that requires
The feeder should have been sized for the service to the house i.e. 200A
so unless you replace the panel with say a 400A un it, the feeder should
have been sized properly. What that feeder size should be varies a bit
from utility to utility and one of their engineers should be able to
tell you what size a 300' drop for a 200A service should be. The NEC
code has some guidelines for service drops, however utilities follow the
NESC, not the NEC so they may not match what the NEC recommends.
Remember that unless the service is absurdly overbuilt you will have
voltage drop as load increases. The voltage delivered by the utility
will often vary a bit over the course of the day as well. What is
considered an acceptable voltage range measured at the meter socket
varies from utility to utility as there isn't one national standard.
Something like 117V - 127V would be a fairly typical acceptable range
measured hot - neutral.
When I upgraded from 100A to 200A the power company was happy to do the temp
disconnect for free but if I wanted to upgrade the feeder it would have been
at my cost.
In my case I was upgrading to get a newer breaker panel to comply with code
requirement (AFCI breakers) and wasn't adding any significant load, just
dividing it up differently. If I were to add A/C or similar heavy load, it
was recommended I upgrade at that time. Fortunately for me it will only be
50' of unobstructed overhead, won't take them an hour when the time comes.
As it is, when I switch on a 12kVA load, I see barely preceptable dimming on
all branches, not too bad at all.
The electric company doesen't want to spend the money to replace
the feeder, and is bullshitting you. If your electrician knew anything
about the principles of electricity (or was familiar with the games of
the electric company in your area) he could have told you this.
I tend to agree with you but how do I get them to do the right
thing?...We tried suggesting that the dimming was degrading our
appliances but..all they will do is test the line ..We are concerned
that ultimately it will shorten the life spans of the motors..Let alone
the annoyance. Its amazing I lived in house built in 1865..no issue
build a house in 2003 ..and this what i get.! Our home warranty refused
to cover any repair..
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