I have been having a problem with my computer speakers. They, for
no apparent reason, start buzzing very loudly. I've determined
that, if the speakers are powered with a slightly high power line
voltage, they will indeed buzz. I tested this by plugging the wall
wart into a Variac and monitoring the voltage with a DMM, not true
RMS, actually a Fluke 8020A.. At about 126 volts, the buzzing
starts. Today I came into the house and noticed beeping from my
computer's UPS. It was definitely in the "power out of range, use
the batteries" mode. The inverter was humming and there was some
heat coming from the heat vents on the UPS. After checking around I
measured the line voltage at 127 volts. I thought this was a bit
high so I called the power company. They indicated that this was
NOT considered high, but are sending out a tech anyway. So, my
question to all you experts out there, what is considered high? My
UPS thinks it's high. My speakers don't work, but, I know they are
I'm not an electrician, but I was always told AC power should be 117
VAC + or - 10%, which is 106 V to 128V.
So 126 V is definitely on the high side, but within tolerances. Of
course, the tolerances percentages may be different for the UPS. I
would check the operating specs for the UPS to verify that.
from Duke Energy and said that the voltage wasn't that high, but as
the above answer said, it was on the high side. He called into his
office. They had him make some checks of the power at the
transformer on the edge of my property. This transformer serves 2
houses. A few minutes later I got a call from Duke saying that they
had a problem at the substation and were dispatching a crew there to
fix it. I continued to monitor the voltage. I saw a maximum of 129
volts and shortly thereafter is went down. It's now hovering at
about 115-117. And my UPS is now happy and I guess I am too.
room in your home. If they all read the same, the cause is more likely
to be the power company. However, if you find any that read
substantially less, especially if some are below 110V, you are likely to
have a bad neutral - probably where your service is connected to the
lines that service your neighbors. That usually will cause an imbalance
between the 2 115V arms of your 230V service.
I had such a problem several years ago. My kitchen appliances were
overjuiced and my bedroom lights were dim. My power company refused to
consider a visit until I spent over $100 to get an electrician to check
out my home wiring first. His diagnosis, bad neutral before my service
line entered my distribution panel. When I told this to the power
company, they came, they checked, they agreed, they dug, they repaired.
Good luck! P.S. They refused to reimburse me the electrician's fee,
even though I thought that I was entitled to it.
Residential Voltages are specced to be:
a.. Voltage, including tolerance (usually +10 or -15 percentage)
and 120/240 Vac nominals. These are the voltages that must arrive at your
residential meter. Many places online give this spec; just look for them.
Barely, but within tolerance. I had a problem with bulbs burning out and
they seem bright in the morning. Checked my power and had 140 volts in the
morning. They said the voltage is kicked up in the morning as industry
comes on line. They made adjustments and no problems since.
127V is or was considered the top end of the allowable voltage range.
When I had my UPS beeping and displaying 136V which I verified with my
Fluke 87 as 135.6V the utility was remarkably quick in responding. The
CSR I talked to had no idea what I was talking about but promised to
relay it to a tech. Sure enough within 10 min I got a call back from a
tech and gave him the report. Another 10 min later there was a truck in
my driveway and by the time I got out he had already checked and was on
the radio to another tech heading to the regulator bank up the street. A
short while later I had a nice 126V. Less than an hour from call to
resolution, pretty impressive really. No problems since then either.
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