How To Do You Measure the Quality of Your AC Power?


What is the best way to measure the quality of the AC power feeding your listening room? Is there a device you can plug into an outlet that will give you the voltage, frequency, the total amount of distortion relative to a perfect sine wave, etc.? Furthermore, how would you measure the ability of your AC main to deliver transient currents?
It seems like there may be a scenario where you could measure your power quality to be excellent but somewhere in the line you could have a loose or poorly made wiring connection which under heavy load (such as powerful bass notes) you could run into trouble with power delivery. In this scenario, an AC regenerator would not help you, or would help very little.

Just curious what methods people have come up with to systematically analyze their power and how they use those measurements to drive buying decisions or repair work, if needed.

Edit: My apologies for the title typo.
Previewmkgus
A little backstory for the curious: When I moved to my current house, my audio quality decreased substantially. I spent a great deal of time investigating this and believe I’ve narrowed it down to the AC main. Multiple electricians have failed to find anything wrong with my electrical system or electrical panel. At this point, I believe the power quality from the city may be poor but I’m not sure how best to measure it. I also have a hunch that there is a loose connection somewhere between the utility transformer and my breaker panel. Before I bug the city, I would like to be able to provide measurements that something is wrong, but I don’t know how best to do that. Also, from a recent utility locate, it looks like the underground power goes from the transformer to my neighbors house and then to my house. Is that standard wiring procedure?
Hire a Power Quality Testing Company. Cost per hour $150 - $250. A heck of a lot cheaper than buying a Power Quality Analyzer.
Example of a Power Quality Analzer:
You would only need one for single phase power.
https://www.myflukestore.com/category/fluke_power_quality_analyzers

At this point, I believe the power quality from the city may be poor but I’m not sure how best to measure it. I also have a hunch that there is a loose connection somewhere between the utility transformer and my breaker panel.

Before I bug the city, I would like to be able to provide measurements that something is wrong,
Bug the Utility Power Company first.
Call them and ask who you can talk to about your power problem. Usually it will be an EE. Nicely ask him/her if a tech could come to your home and check for a problem(s) from the load side of their meter to their utility power transformer. Again, nicely ask for their help.

The tech will pull the meter and visually inspect the meter socket electrical connections for corrosion and for any evidence of a loose connection. He may even check the mechanical lugs for tightness. Loose and or corroded terminations can cause harmonic distortion on the mains. If everything looks good in the meter socket hopefully he will plug in a device that will allow the tech to test for power quality. He will plug the meter back in to the device and will return after a couple of days to review the collected data. The tech should supply you with a hard copy test report.

Sometimes the tech will connect the power quality analyzer at the main electrical service panel ahead of the main breaker. It just depends on the Power Company’s testing policy.


FWIW. A single phase 240/120V electrical service fed by an overhead power line will have a minimum of 18 to 22 electrical connections from the transformer to the Line side of the service equipment main breaker and service entrance neutral conductor connection in the service equipment enclosure/ panel.
Most of the electrical connections exposed to the elements, harsh conditions, of mother nature.
Wind, heat, cold, rain, high humidity, snow, and ice.
.
What a freaking waste of time and money. None of these people will find anything wrong, because from their point of view there is nothing wrong.

Multiple electricians have failed to find anything wrong with my electrical system or electrical panel. 

Exactly. There is nothing wrong. Sorry, but there just isn't.  

Only thing wrong is your approach. You heard a difference and assume this means there is some glaring fault somewhere to be fixed. There isn't. Instead there is just the normal problem of noise coming into the line.   

The kind of noise we are talking about is endemic, and involves everything from RFI from radio, cell phones, and appliances, to EMF from everything connected to power everywhere.  

It is what it is. What you do is what everyone does. Make all your connections from the panel to your room as clean and tight AND FEW as possible. This is where the "dedicated" (which really means direct) line comes in. Then from there you use as good quality outlet, power cords, and conditioner as you can.   

The better the quality, the better the results. Results which are by the way determined by ear, not by meter. Unless your system goal is to sit in the dark looking at a meter?
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Maybe, but maybe not. What I have noticed about electricians and electrical engineers is that they approach it from the perspective of meeting code and not starting fires. That’s not a bad thing in general, but if you’re chasing high fidelity sound you’re going to have a bad time with that approach (minus the not starting fires goal, haha!)

If code allows for a 5% voltage drop in a 120V line, then you’ll see fluctuations between 114 volts and 120 volts depending on the load. That’s completely unacceptable for hi-fidelity sound. You want that voltage sitting at 120 constant and not budging an inch. Sure, a good power supply will minimize the effects of voltage fluctuations but why would you want to deal with that hurdle if you don’t have to? Make it as easy as possible for your equipment to perform, which means going well beyond what a code book would tell you. 

Your advice with a dedicated line is spot on, however, it won’t fix problems upstream of your panel such as a loose lug on the meter socket. There are other things going on outside of my audio system that strongly indicates a poor ground or bad neutral connection.

I could pull a dedicated line, I could buy a filter, I could buy a regenerator, and I probably will some day, but there has to be a better method than “just try whatever and see what helps.” If you can diagnose the problem properly, then you can apply focused solutions which saves time, money and headaches.
Early in 2020, on the recommendation of my electrician and @jea48, I contacted our Power Company and requested a power quality analysis. They installed a special meter and downloaded weekly readings for a month. It resulted in some repairs to our service, and to neighbors’ service. One repair improved voltage consistency. 

It was free. Well worth investigating.
That’s exactly the type of thing I wanted to hear about, tvad. Thank you!
Besides poor audio quality, two examples of what I’m experiencing are:

1) Playing music with bass at low to moderate levels causes dimming lights.
2) Slowly walking on a treadmill causes the lights in the room to substantially dim with each foot step.

I’ve had electricians tell me that the best way to wire things is to have the lights and outlets on separate circuits so that things like treadmills don’t dim the lights, but there’s just no way a slow paced walk on the treadmill is pulling down the voltage that much on a normally functioning electric service. The problem seems to affect the whole house which makes me think it’s upstream of my panel. I’ve had all the lugs in my panel tightened and I even dug up the top of the ground rod to verify it’s connected and it is.
What a freaking waste of time and money. None of these people will find anything wrong, because from their point of view there is nothing wrong.

Multiple electricians have failed to find anything wrong with my electrical system or electrical panel.

Exactly. There is nothing wrong. Sorry, but there just isn’t.
Qualifications of the electricians? Years of experience in troubleshooting?
Were the electricians just residential electricians, or journeyman electricians with years of hands on practical experience troubleshooting electrical problems in commercial and industrial facilities? Yeah, it makes a difference.

Here is what an average electrician should do, and check for, in an electrical panel.

1) check voltage. Line to Line and each Line to neutral. He/she should also check Line to EG bar voltage to verify the Main Bonding Jumper is effectively bonding the service entrance neutral conductor to the metal enclosure of the panel.

2) Hopefully the electrician has a Thermal Imaging Camera to check for corroded and or poor electrical connection hot spots. Or maybe he/she just has a cheap temperature sensing handheld device for checking for hot spots. (All loads should be turned on if possible. Especially high amperage usage loads).
Corroded and or loose connections can cause series light arcing which in turn can cause harmonic distortion on the mains. Even bad seating contacts in a breaker(s) can cause harmonic distortion on the mains. That also goes for the Main breaker. Same goes for the Line side connection of the breaker to bus tie connection.
Did any of the electricians have the equipment to test for temperature hot spots MC?

3) If no hot spots are detected the electrician still should look for any signs of corrosion at all wire to breaker terminations. Especially on the service conductors feeding the main breaker or main lugs, if the main breaker is elsewhere. You would be surprised how many service entrance conductor terminations at the electrical panel show signs of corrosion.

4) The electrician should check the Grounding Electrode System for corrosion and tightness of all connections. (Grounding electrode system is the wiring and clamps used to connect the service entrance neutral conductor and service equipment enclosure to mother earth.

5) If the panel is fairly old and has aluminum bus the breaker to bus tie connection should be checked for possible burn arcing hot spots. Especially known loaded branch circuit breakers.
Go through all the electrical connections in the panel for wire to terminal tightness. Conductors to breaker terminations. Neutral conductors to neutral bar terminations. And EGC to EG Bar terminations. Check tightness on service entrance conductors at main breaker or main lugs. Check service entrance neutral conductor lug for tightness.

FWIW I have read at least 4 threads on various audio forums over the years where the OP asked basically the same questions as the OP on this thread. In the end the problem was found in the meter socket of an overhead fed electrical service.
Rain water over the years can find its way through the weather head and inside the mast conduit and travel down the conductors and collect on the Line side of the termination lugs. Over the years the water causes corrosion and causes the connection to deteriorate. That in turn causes a small amount of series arcing in the connection(s). That in turn causes harmonic distortion on the mains. The greater the connected load on the corroded connection(s) the greater the percentage of harmonic distortion on the mains.

It won’t cost the OP a PENNY to call the Utility Power Company. Just a little bit of his time.
Or just take the advice of MC. He will tell you "He is the only one here that has actually done it".....  

Best regards......


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I don’t think the electrician did any of that. I should have hired you! I think it was more of, “Well I tightened what lugs I could and no breakers are flipping so you don’t have a problem.” Thanks for all the good advice.
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Make sure your switches and outlets use real wire wrapped screw tightened connectors.

The little hole for the backstab connections are poor and I'm not even sure they are legal anymore. 


EMI:  Time domain (i.e. oscilloscope) measurements are more relevant than frequency-domain ones (i.e. spectrum) simply because spectrum analyzers (with the exception of really expensive ones) would miss transients which dominate the type of electrical noise present on power lines and ground.   Measure both common mode (i.e. between Live/Neutral and ground) and differential (between Live and Neutral).  Here is an article I wrote on the subject for inCompliance Magazine that deals with these things: https://incompliancemag.com/article/measurements-of-conducted-emi-in-the-manufacturing-environment/   The tools to use: a portable digital scope (I use Hantek 1200 family, but others can be just as good - just make sure that the bandwidth is at least 100MHz), and power line EMI Adapter MSN17 (https://www.onfilter.com/emi-adapter-msn17) otherwise you won't be able to make any relevant measurements and can kill your oscilloscope.  Stay away from the tools that give you fuzzy relative data and no specification.
If you are interested in harmonics, you can use the same oscilloscope (make sure it has FFT - most do.   Read the user's guide!) and 100:1 probe.  Scope must be in battery-powered mode only!  Unless harmonics are quite severe (at the factories I have seen quite a bit, but not at homes), they are unlikely to affect anything of importance in this case.
They make tools for evaluating and testing your power to your house but i would try to just run a dedicated line to your stereo and that should help significantly for you sound and be sure to connect all of your equipment to the dedicated line so it is all at the same ground potential.
take the advice of MC. He is the only one here that has actually done it".....  

To wit:
What you do is what everyone does. Make all your connections from the panel to your room as clean and tight AND FEW as possible. This is where the "dedicated" (which really means direct) line comes in. Then from there you use as good quality outlet, power cords, and conditioner as you can.  
The better the quality, the better the results.
Strip away all the blather above and this is what you get. Every time.
@Mkgus  You could look at our purchasing a line conditioner.There is one made by Trip lite I think it's around 90 .00 it will not only protect against spikes but it regulate the voltage. If the voltage dropped to say 85 volts on your circuit feeding your audio system it we correct it to 120, also if it went to high say 130 it will also correct back to 120. Also a whole house surge suppression ( breaker) depending on the panels manufacturer would also help protect the circuits feeding your audio system as well as rest of the house. If you have power and all seems to work fluctuations are tough to troubleshoot and actually repair some people don't know there occuring. The conditioner will help with some piece of mind yes I have a clean 120v for the circuit.
Sounds like a classic bad mains issue. I had a similar issue with dimming upon load. Turned out to be a bad connector on one of the 120v mains on the power pole. As many above have suggested, call the Power Co. If mains are good, find a better electrician. Beyond that, the rabbit hole is deep.... An isolated ground circuit is helpful, but still shares grounding at the box. I like an a large ungrounded (yeah probably not to code) isolation transformer (larger than the sum of VA or watts of the equipment) to start..... 
None of these people will find anything wrong, because from their point of view there is nothing wrong.

Perspective is everything.  Last year I was checking the electrical in a place in Ixtapa.  Found all kinds of problems from reversed polarity on wall plugs, missing ground wires..........    I asked a local "electrician" if there were any standards they followed when wiring a home.  He asked me "is the fridge cold?  Do the lights come on?  Then what is the problem?"   
Just one problem with an ungrounded isolation transformer: some manufacturers ground a metal case to the ground pin, and count on it to prevent electrocution in the event of malfunction.

Don’t get me wrong - I use isolation transformers for everything. But unless I built the electronics myself, I just grit my teeth and ground those transformers. To code.
Thank you  Jea. Nice display of patience.
I used a $20 meter and could tell that my voltage was fluctuating quite a bit during the day which was also moving the bias on my power tubes quite a bit.  I ended up trying a PS Audio regenerator and they gave me a 30-day return period if I didn't like it.  I discovered the THD on my line was at times over 4% and the unit brought it down to less than 0.1% while also blocking nearly all DC that might be on the line.  The regenerator substantially improved my sound quality and also massively reduced the noise floor on my SET amp while also providing electrical spike protection.

Here's a screen shot from a few moments ago of the display.  You can see it's taking the incoming 3.8% THD this evening and dropping it to 0.1% while also correcting the voltage to 120V and keeping it there.  My tube bias never wanders at all now and the system sounds fantastic.  I have no SQ fluctuations over a 24 hr period anymore and all my gear is plugged into it.  I'm not a huge fan of PS Audio gear other than their regenerators - this is what they really got right IMO.

https://i.postimg.cc/MKQR7Nqm/Screen1.jpg
The quality of the mains sine wave does not matter too much as long as it is able to magnetically excite the transformers of your electronics.  Also noise, including RF noise is usually very well filtered out by good quality power supplies. What remains is the current delivery capability of your circuit when it matters. And that is usually dictated by the quality of the internal wiring of your house. İf you are noticing dimming, that is indicative of too much voltage drop in your wiring. İs your house wired with a lower gauge wiring ?  Or is it an older house with aluminum wires ?  Are there any loose, corroded or bad connections from your panel to the plug ?  İs there any 'coiling' of your wire anywhere, causing inductance which resists current delivery if it becomes significant enuf ?
Dimming lights from an exercise machine???????????

That's serious.  No-one else gets that, although I used to get it when I powered up my old Krell.
Sounds like you've just got bad or old or damaged house wiring.
Get a competent electrician to re-wire the house.  Put the hi-fi on a dedicated circuit back to the company fuse with 20 amp wire.
Then enjoy the music!

@jea48 Thanks for the very practical answer and to @tvad for the tip on contacting the electrical company. We'll see how they react, and if they can come out, I now have a practical list of what to ask them to check.

I've asked this question before on threads and this is the best answer I've read to date. No condescension, just expertise. Appreciated, Jim.

I could never figure out why the load on the two legs has to be balanced, do your electric devices all turn on and off at the same time? There is always going to be an imbalance.
@hilde45:
@jea48 Thanks for the very practical answer and to @tvad for the tip on contacting the electrical company. We’ll see how they react, and if they can come out...

Tip: My electrician said to tell the Power Company that we had a problem with dimming lights, which would provide a reason for the Power Company to do a power quality check.

The Power Company found a neighborhood transformer that needed replacing, and they also found something on our power distribution pole that needed replacing (as well as a few neighbors, so they benefitted too).

They also tested every breaker in my panel for continuity (I think the term was continuity...it’s been a while), and said quite a few were out of specification and should be replaced, which I had my electrician do.

Thank you to @vk_onfilter for directly answering the OP’s question.
Dimming lights? Treadmill affecting things? Let's start with something simple!
Most modern outlets use some sort of wire capturing spring. They're quick and easy to install. Strip and insert wire, done. While they may hold the wire fine, IMHO they're crap for a SOLID connection. If you're competent enough I'd suggest the following: Kill the power at your breaker box. Pull the outlets in your audio room and redo the connections using the *screws* on the sides of the outlets. (Or have an electrician do it, even better.) This will give you more conductive surface area and a more SOLID connection. I've done this in a couple homes I've owned and it made all the difference. No more dimming lights during loud, bass heavy music. Good luck!

Happy listening!
Hell,  20 years ago I found the best electrician I could find, he replaced my old service, weather head and tidied things up In the attic. 
He had the power company come out and they either on his advice or theirs,  put a pole in my yard with a transformer on it, it was at the street before. I'm in a rural area and the poles on the side of the property,  Ran new larger wiring from the street to my new service panel. I'm looking out at the now closer transformer and larger service than before. 
The power company will help you out. 
The utility company works within a high range and low range of acceptable. As long as their test comes back within that range they will do nothing. You could be at the very bottom of said range but still considered acceptable. You need to do the rest on you own with a quality power conditioner and good cables. 
The responses above vary so much between “the power utility will do nothing so long as you have electric service” to “the power company will really help you with testing and equipment changes to arrive at a high quality of electric service.”   So, it really varies that much from one locale to another, and it is the luck of the draw what assistance you will get?

My experience (not particular to electric service or its affect on sound quality) is that the utility always wants me to have a professional check and repair problems within the home first before the utility will send anyone out.  The technician, having checked a few things, says “I checked the box and your outlets, so if you are still having problems you will need to call the utility . . . Just what are you trying to do? . . . Oh, I don’t know about that. I just verify that you have electric service and you do.”
The utility company in my area uses higher gauge wire than what is used for the service feeder. I guess they don't have to worry about the wire getting hot because it's in open air.
The dimming lights synchronized with bass notes or walking on a tread mill is a dead giveaway that power is a problem. When contacting your power company make sure you tell them about this problem up front. They should take you very seriously just based on this one factor. Even a 15 amp standard circuit should not experience a significant voltage drop from a typical Class A/B amp running at normal volumes.

The dimming lights are a result of voltage drops when there is just a modest demand on the circuit. That means that no power conditioner will solve the problem. You are going to have to tackle the source of the issue which is your power (you knew that).

When approaching your power company I would suggest that you communicate that this is concerning you from a safety perspective. Don't just complain about your SQ - some people might just roll their eyes and blow you off. When you say the word "Safety" they are going to perk up and listen. Tell them that you have researched this symptom and found that it could be an indicator of a serious problem in your electrical service.

If you don't have a multi-meter you can pick one up for about 50 bucks. You can do a simple check of your AC voltage and you can get a sense of how much the voltage is dropping when you crank up your system. This will be good information to have if your power company responds poorly.

Thanks to jea48 and a few others for excellent detailed information. Except for the usual snarky drivel this has been a very informative thread.
Take a look in these videos from Shunyata Research. Power is their area of expertise. You may find some practical guidance on them. Good luck.
https://www.youtube.com/watch?v=4qCK--lRFd0
https://www.youtube.com/watch?v=LHXP19fXN60&t=39s
https://www.youtube.com/watch?v=Z6f1kwyZbM8&t=35s


I have a dedicated line into my system. 
Pretty quiet. I have had few problems.
Dirty electricity https://m.youtube.com/watch?v=18qneiDgR1E
It's more than just sound, it affects your health.
Stetzerizer filters and meterhttps://www.stetzerelectric.com/

I use to get hertz frequency readings around 600!! When every device needs 50/60.
Cleaned the sound immensely.

Peace and Freedom of choice.

Gian


I do not think there is a "one size fits all" solution to troubleshooting electrical system problems. My power company came the same day I called to do some perfunctory testing of the service entrance and all was good. I had found a few spots in the system- funky xlr connector (which the manufacturer re-terminated at no cost) and a bad tube socket (which I had help replacing). Despite having gone to some lengths to set up a good electrical "subsystem" for my hi-fi shortly after I moved here 4 years ago, I still had an occasional intermittent burst of static, even after replacing every tube (I have tubes all the way through, from phono section and power supply to line stage to amps- a lot of tubes).
I think I was finally able to diagnose the problem with the help of the designer of my line stage. He suggested I pull the battery packs (it runs on lithium batteries when playing) and swap them. I noticed some dust between the battery packs and the plates where they make contact. So I dusted those while swapping them L-R and R-L.
System is now functioning as it should.
One thing I do recommend is a commercial electrician. I’ve done several rooms over the years and my experience with commercial electricians generally has been better than the garden variety residential person. Not to paint with a broad brush, but as @jea48 mentioned, there is a wide variety of experience and knowledge among those who do this stuff for a living. The guy who ran my project did not specialize in sound or studios, though they have done them-- they work on all kinds of big institutional stuff. Trick is finding a service company in your area that does both residential and commercial, since a lot of commercial electricians don’t want to bother with what they consider to be small residential household issues.
I’d also counsel patience- I know, you want it right and you don’t necessarily want to throw money at it in the hope of some band-aid. I’d start with the power company and find a good electrician who is savvy at troubleshooting. It could be something small.
For example, in a previous house, even with dedicated lines, there were certain appliances that could be heard through the system. Simple solution- avoid using those when listening.
I know people rely on power conditioning as an quick solution-- it may not solve the problem, but my bigger issue isn’t that- it is what the conditioner does to the sound. You may hear a difference with conditioning, but that doesn’t necessarily mean better. I’d try to solve the problem before I resorted to "conditioning" simply because filtering out noise is likely to filter out information you want to hear.
Good luck with this. You’ve gotten some good input here.
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I use PS Audio products which can measure the amount of incoming THD which is usually in the 3% plus range for me. After regeneration, the THD drops to the -0% range. I feel that that method of measurement and subsequent cleaning of power is beneficial to the overall sound quality. 
Additionally, I have installed Environmental Potentials EP-2050 power line industrial EMI/RFI/spike filter. These are used in massive server farms, IT systems, medical electrical systems, large corporations where critical systems rely on flatline clean power delivery. 

On cables, especially newer Shunyata with DCT to help with noise, hmmm, they are able to lower noise floors below the already impressive -0% noise floor. Can we even hear that? I mean really, can we hear that level of noise reduction or is it already below the perceptible hearing level that would make a difference. What  does a .0001 noise floor sound compared to a .001 noise floor? Can you hear it? Power cables are part of recipes…many in the community hear differences in what power cables do, myself included. Heck, my stock cables sound different, and better in some positions in my system than other power cables. Ahhh, different….what’s that? Noise floor, hmmm. Did that new cable lower the noise floor and I heard it, or, did it change the perceptible audio spectrum which alludes to more recessed mids, increased bass, and sizzling higher frequencies. Look, power cables are like ingredients in a recipe. They can alter the soundscape, but, be careful what you ask for. Power delivery by any cable to your system by default is going to be great. When changing out power cables, all you are doing is changing the ingredients in the power delivery chain which may or may not change the flavor of your sound. Trust me, I just splurged on a half dozen Shunyata Sigma NR 2s and experimented with different power configurations and each component reacts differently to power cables, sometimes to the detriment of sound quality. Get your ingredients right and in the right order. Another example of new Sigma NR2s in my system…my volume must be turned up at least 1/4” higher to get the same loudness level as before. So much for instantaneous power delivery of cables. My system already jumps out at you with instant speed and can play loud as heck…but, power cables alter something, maybe the background is quieter, but why? Ahhh, my highs are slightly veiled and lost some organic sound qualities. Switch the ingredients, maybe new cable break in. Another cable ingredient to consider. 
 I agree with other posters about your electronics and amps having the ability to cope with power anomalies to a certain degree which still results in awesome musical enjoyment. 
Methodically evaluate what you do and do it in small steps. Sometimes, the little things are the biggest payback in musical enjoyment. 

Most audio components are completely immuned to dirty mains power. There are some exceptions (some Rogue Audio stuff for example), but otherwise, the most common problem is humming/buzzing toroidal transformers from DC offset. This is something your power provider can check for with a special meter. They should do that free of charge if you have a legitimate concern. 

https://youtu.be/OL23xkLfPTU

If dirty mains is an issue, it’s best to just stick with the bigger name brands that have competent engineering chops. 
As mentioned many times above (very good advice) it seems like you have a voltage drop problem for whatever reason. Please pursue this with the appropriate pros as detailed above very well.  

If you are curious to "see" what's happening for yourself you can purchase this at Amazon for ~$28.  It will read out true RMS voltage continuously.
https://www.amazon.com/Poniie-PN2000-Electricity-Electrical-Consumption/dp/B0777H8MS8/ref=sr_1_3?cri...

I find mine very useful in the watt readout with individual pieces plugged into it.  Simply to see start start-up wattage versus idle wattage.

Plug this into the wall and plug the treadmill into it. 

This suggestion in no way negates your need to find a true cause.

Regards,
barts
I'll add in my $0.02 for what it's worth on the subject.  To answer the OPs question I don't concern myself with EPQ measurements of any significance.  For me, conditioning the incoming power is a very basic requirement to cleanup the harmonics and spikes you receive at the house.  I use legacy Monster brand conditioners on my primary and secondary audio systems.  These read a constant 120.1 vac all day long, and I'm good with that...condition it, fahgettaboutit! 

Is your incoming dirty?  Absolutely.  Is it a pure sine wave and distortion free?  Ha, no way!  Here's why. 

Power starts with a turbine/generator at your local station, leaves the building at 23 kv or so at a rock solid 60 Hertz.  From there it feeds numerous auxiliary/station service transformers (tx) and hundreds of motors back inside the plant.  When it leaves the building it hits generator step up tx units taking it typically to 230 kv, then 500 kv in the switch yard for transmission. 

Every tx adds in a bit of influence, and harmonic distortion especially in the 1st and 3rd orders up to the 21st order or so.  New tx included,  but even more so with aged units you also have internal partial discharge and external corona over a wide band of frequency ranges . IEEE/IEC standards dictate what level is acceptable for the particular vintage, class, kv and size of the tx .  Anything over 21 kv to ground will go into air corona unless shields are installed. Count in dozens of switchyard breakers, each with internal and external connections, as well as bushings, connectors, buss conductors, tap changers, wire, terminations, lightning arresters, insulators, switches, ground connections, cap and inductor banks, so forth and so on.

Leaving the switchyard down the transmission corridors the feed travels for miles; in my state there are over 30,000 miles of transmission and many hundreds of feeder substations to step down the power for distribution at low voltage, 25/14.4 kv and12/7.2 kv are common.  In these stations... more switches, breakers, tx, connections, etc. and miles of wire on the street.  I`m lucky, the closest generating station is < 20 miles from the house, and the closest substation is <6 miles away.

Regulators (regulating tx) constantly jog the distribution lines based on loading to keep voltages at your neighborhood, when stepped down by those little green boxes (or grey garbage cans on the pole) close to 240/120 volts.  These can be set to narrow or wide tolerances but keep the incoming between 115-125 vac at the kitchen outlet.  Is that dirty? Yes indeed.  Will you ever receive a pure sine wave off the street? Nah.

If you hang an Agilent or other such really high Q analyzer on your lines you would likely see flat tops and transient spikes in the voltage trace.  Harmonic distortion in the current trace will look more like a sawtooth than a sine wave.  Google spends millions on power conditioning at their data centers. As an audio aficionado I spend a little.

Every large utility will have an EPQ group, 8 or 10 guys and gals to investigate significant power quality issues.  Hospitals and industrials come first followed by commercial, the lonely chicken rancher who has
5 or 10 acres and 10,000 chickens that wont lay eggs, then Mr. & Mrs. Residential.  If you have a critical medical device in the home you just got upgraded.  Reach out, be cordial, ask for help.  It's what they do.

Most significant issues will likely be found in the ground connections. 

I hope I've added some value to the discussion.  Every time I flip a light switch, and the light comes on, I just smile a little bit.  Freaking miracle that is!


Lots of good advice here save the link to the ASR clowns. Anyway, there are meters available (Entech, for example) which can measure a degree of noise in your home. My wife and I flip homes and do a majority of any electrical work in the renovations. Prior to buying, I measure the mains noise with an Entech meter and a Stetzerizer. Some readings come in low (<100) while other peg the meters out- these mostly in high rise condos- I avoid investing in these places. As JEA48 pointed out, often the problem can be from loose breaker terminals in the electric panel, especially in newer homes. FWIW, I am an electrical systems technician and can say that most service calls I go on have a common denominator- bad connections- by the prior service tech, of course!
If your power source is questionable you can install a line conditioner.  A good line conditioner will filter out noise in your power signal.  Often used in industrial control applications to feed clean power to the control system.  This power source should also be supplied from a panel dedicated to sensitive equipment.

If you really want the cleanest power you can get a dedicated panel installed for your AV equipment.  Professional recording studios do this.
Just wanted to say thank you to everyone that replied. There is a lot of good information here and I’ve got some good paths to go down. Will definitely call my utility and follow up on that.
Hi mkgus,

Twenty years ago, when we and the bank purchased our home, the lights dimmed when the fridge and furnace powered up.  A phone call to the Central Maine Power Company brought them out immediately to test.  The following Sunday at 10am, they installed a new pole, transformer and lovely ground outside of our house.  I later learned that on weekends, stand-by crews will often do the odd job, keeping them busy.

My supportive Master Electrician (who works Nuclear Submarine Panels, at nearby Bath Iron Works,) later isolated the two dedicated studio lines on our electric panel, away from the big power draws.  Over time, I've upgraded to a Furutech outlet w/cover plate, along with a replacement male Furutech plug for my hardwired Panamax M4300-PM line conditioner.  I suppose it's obvious by now that after 45 years of hi-fi, I consider isolated power and good wire no less essential to great sound than equipment choices.  For me, our hobby is a process, each improvement freshening our collections and triggering our passions. 

Now, let the eyerolls begin.  My most recent system addition is the Furutech NCF Clear Line AC power line optimizer.  In a small studio, I am always looking to add depth and MUSICAL micros to my soundstage.  It accomplishes that.  A caveat; I have no affiliation to Furutech and elect to  buy their products from The Cable Company, keeping away from black market concerns.  I'm always happy to pay full price in support of premium products.  

Thassaabboutit!  More Peace, Pin
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Thank you for sharing your experience. Clean power is vital!

Quick update: I called my utility company and they sent someone out immediately. They discovered that the neutral lug on the homeowner side of the meter was loose and the bolt is stripped. An electrician is on the way to replace the neutral lug. 
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