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Author Topic: AC outlet  (Read 985 times)

Keith Broughton

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Re: AC outlet
« Reply #10 on: January 21, 2014, 10:17:44 am »

I just tested the outlet out of curiosity and this was the result.  No real problem.  Is this something I should look into further with the utility company?  Is it unrealistic to think that outlets can deliver a clean power ( clean sine wave )?
I would say it's unrealistic to get a pure sine wave...IMHO
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John Roberts {JR}

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Re: AC outlet
« Reply #11 on: January 21, 2014, 10:49:14 am »

The only time I ever called my utility was when my home outlet voltage hit 130V one night and was still climbing. I noticed that my incandescent lamps were unusually bight.  The guy on the phone didn't believe me, but it was slow night so they sent out a truck. They metered my drop and discovered I was not imagining things, and then fixed "their" problem at the sub station.

Waveform purity is generally not a major concern unless it gets significant. I am not aware of throwing distortion analyzers on mains power being common practice.

JR
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TJ (Tom) Cornish

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Re: AC outlet
« Reply #12 on: January 21, 2014, 11:21:55 am »

I just tested the outlet out of curiosity and this was the result.  No real problem.  Is this something I should look into further with the utility company?  Is it unrealistic to think that outlets can deliver a clean power ( clean sine wave )?
Nope, and Yep.

This doesn't look unusual to me, and as JR said, since you're still getting 123 volts, it's perfectly within spec.

We spend a lot of time fretting about "power quality", but unless things are really bad - much worse than your scope trace shows, things are totally fine.  The biggest issue we face is voltage drop from high-current loads at the end of too long/too small cords.  Our industry should host a mass bonfire to rid the world of 16-ga orange extension cords, followed by mass psychotherapy to rid the idea that that 20,000 watts of amp power and 100,000 watts of PAR lights are necessary for 50-cap bars.

On a related note - some folks say that generator power is cleaner than the mains.  This is true in many cases - scoping the output of a Honda EU generator looks textbook great - until you actually start using the generator - then you're back in the same game as with any other power - it's the load that messes up the power, not the source.  The power grid has a lot of electrical inertia to deal with this - small generators have considerably less.
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Kevin Graf

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Re: AC outlet
« Reply #13 on: January 21, 2014, 12:52:19 pm »

To worry about a clean sine wave from the power company is a total waste of time.  If you examine the current wave form (not voltage wave form) to a power amplifier, you will see a wave form with between 75% and 150% THD (Total Harmonic Distortion).
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Tim McCulloch

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Re: AC outlet
« Reply #14 on: January 21, 2014, 01:23:14 pm »

To worry about a clean sine wave from the power company is a total waste of time.  If you examine the current wave form (not voltage wave form) to a power amplifier, you will see a wave form with between 75% and 150% THD (Total Harmonic Distortion).

Plus 1, bingo, etc. Not sure why the OP thinks this is even worth pursuing.
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TJ (Tom) Cornish

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Re: AC outlet
« Reply #15 on: January 21, 2014, 01:39:23 pm »

Plus 1, bingo, etc. Not sure why the OP thinks this is even worth pursuing.
OP was trying to learn.  I have no issue with that.  Much of one's success in life is being able to tell the difference between things that matter, and things that don't.  Now the OP has one more thing to add to the "doesn't matter" list.  I'd like a few more of those in my life, too.  :)
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Jonathan Johnson

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Re: AC outlet
« Reply #16 on: January 21, 2014, 01:49:32 pm »

To worry about a clean sine wave from the power company is a total waste of time.  If you examine the current wave form (not voltage wave form) to a power amplifier, you will see a wave form with between 75% and 150% THD (Total Harmonic Distortion).

Yep. A lot of people (not accusing the OP of this) are conditioned to expect perfection in everything and are unwilling to accept reasonable variations from the ideal**. They simply don't understand what constitutes acceptable deviation, or why. Pretty much everything (except anally-retentive consumers) can tolerate some irregularities in the delivered product, whether it is the water going to your dishwasher, the gas pressure to your furnace, or the electricity to your whatever.

I applaud the OP for asking here before complaining. Seeking information -- "is this normal?" or "do I need to look into this further?" are the right questions to ask. Going to the power company with a zero-tolerance attitude saying "MY POWER ISN'T PERFECT!!!1!!" annoys the power company, irritates those whose equipment generates harmonics if the power company makes them do something about it, and ends up raising everyone's prices in a cumulative, roundabout way. And the customer receives no benefit from perfect power, except for a pretty picture on his O-scope.


**Except when it comes to the spelling and grammar of their own complaints in public forums and social media.

P.S. -- To paraphrase a famous theologian, "Understandest thou what thou meterest?"
« Last Edit: January 21, 2014, 01:52:24 pm by Jonathan Johnson »
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Johnny Diaz

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Re: AC outlet
« Reply #17 on: January 21, 2014, 01:59:58 pm »

The reason why I posted this question is for informational purposes only and would like to thank everyone for their contributions.  I actually never metered an outlet before with an oscilloscope.  When I saw the sine wave I noticed it appeared to be clipping at the peaks and posted it here knowing that the experts would chime in. 
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Stephen Swaffer

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Re: AC outlet
« Reply #18 on: January 21, 2014, 04:27:32 pm »

I worked in an industrial facility and checked the waveform out of curiousity from time to time it typically looked much worse than yours.  That was understandable since we were running a bunch of inverter based welders, VFDs -a bunch of ugly stuff from a noise standpoint.  My understanding is that a waveform like that can cause motors to run less effeciently and thus warmer-but from a practical standpoint it is not worth pursuing unless you are running really big stuff.  My employer at the time only got concerned when the poco decided to charge more because we were causing so much distortion that it affected their ability to deliver clean power to other customers-then we installed PFC correction at the incoming switchgear.
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Steve Swaffer

Josh Millward

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Re: AC outlet
« Reply #19 on: January 21, 2014, 04:28:30 pm »

The reason why I posted this question is for informational purposes only and would like to thank everyone for their contributions.  I actually never metered an outlet before with an oscilloscope.  When I saw the sine wave I noticed it appeared to be clipping at the peaks and posted it here knowing that the experts would chime in.
Which was exactly the right way to approach this kind of thing.

Hopefully this discussion will encourage others to understand the situation and realize why, when they see the same kind of thing that you saw, it looks that way.

Great discussion! This is why I frequent this forum and not others.

Many thanks to everyone who contributes.
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Josh Millward
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