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my quest for a proper ground and sound electric service, need pro advice

my quest for a proper ground and sound electric service, need pro advice


  #1  
Old 09-03-10, 07:20 AM
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my quest for a proper ground and sound electric service, need pro advice

I run a lot of sensitive electronic equipment and pro audio gear, so I am more anal about a perfect electric system than most. My goal here is ABOVE code and not to cheap out - perfect proper and ideal. What I have is sub-par. I am not an electrician but consider myself a competent well educated homeowner, and I check the NEC before anything.

Background:

My 1952 NH home has a refreshed 200 amp service entering the attached garage, and a 4 wire 100 amp house sub panel. Plastic water main entry, no gas. Many 2 prong outlets and snakeskin wiring.

Neutral/ground bonded at main panel, not at sub. *looks* like #6 or #4 stranded copper to building ground (0.250 dia). 2x 1/2" galvanized rods with acorn clamps: First one clearly sawed off god knows how deep, shallow topsoil run to second rod approx 5 feet away. Second one mushroomed top no idea if its sawed off also. not good.

First indication of problem?
I ran 2 side by side fresh 12awg romex dedicated drops - one for home theater one for subwoofer only.
Subwoofer hums like you wouldn't believe.
Break rca ground to receiver it gets better.
Try changing breaker panel leg for both drops to match doesn't change it.
Any large electrical load increase in the house makes hum louder (coffeemaker,microwave,air conditioner, etc).
"cheater plug" to test only did not fix hum alarming me to think there is neutral backfeed!

not sitting well. Home has much unexplained electrical voodoo other than this too. many gfci false trips. Turn on lights and computer ups beeps, etc.

I now suspect sub panel wiring fault or pole wiring fault. I plan to plug the sub in at the garage to see if it has the same issue (my little tester).

My thought/next plan of action is to kill the sub panel main and measure with a multimeter at its feed lug pre breaker for differential and continuity. I then plan to check the main panel feed the same way. Part of me fears that since the problem shows up more under load I wont see anything though. Alternatives?


Building ground should not influence this unless pole feed has a problem, correct?

What and how else should I test? What would you test?

Disconnect 1 of 2 rods to see if it influences service (NOT both for safety in case obviously)?

How can I visually identify proper awg to meter, and from meter to panel? using calipers? If the grounding wasn't done right I want to check to make sure the rest was too...


Also: I began investigating my building ground lately and planned to drive new 5/8 copper rods. I used a harbor freight 1" rotary hammer sds to drive them but they all get stuck around 4 feet. Will renting a 70# electric concrete breaker be my solution to getting these in? is the 600w sds just not enough in tough soil? I would LOVE a deep ground, freeze line is 6 feet.
If I am on a rock shelf what do you recommend to augment my current ground, trenched perimeter run? Removing soil and backfilling with something else?

I know something needs to be done and whats there isn't right. I appreciate all input
 
  #2  
Old 09-03-10, 07:25 AM
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Not into audio like you are by no means, but I think you are misunderstanding the purpose of ground rods. Ground rods are for high voltage events like lightning strikes. They have nothing to do with receptacle circuit grounding.
 
  #3  
Old 09-03-10, 07:55 AM
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And thats what I was thinking. My thought process on "disconnect and see" would be to indicate a problem with the pole drop. If I have to call in the poco I want to be able to prove its on their side first. If it gets worse with 1 of 2 rods it must not have a good pole feed.
My concern for the home grounding is independant, I want to protect my gear.
 
  #4  
Old 09-03-10, 09:19 AM
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Your description of the electrical service all sounds correct, even above-average for the age of construction.

The NEC allows ground rods to be driven at up to a 45° angle to avoid rock when necessary. There are also some other legal electrodes like a ground ring or plate, but I don't think that will make an appreciable difference with your situation.

Your first step should be to eliminate local sources. Turn off all your breakers except the home theater and disconnect any data, antenna, CATV, satellite cables and see if you still get the hum. If it's gone, add them back one-at-a-time until you can identify the culprit. If it's still there, then this is coming from the pole and there's little you can do about it except call the power company and complain.

Also, have you used the audio equipment in another building and not experienced the hum? Make sure it works elsewhere and is not just a bad power supply or something like that in your gear.

Professional audio systems are often run on an isolation transformer to avoid this situation. That's really beyond what can be done at a residence, so a little bit of hum should probably be expected compared to what you might hear at a studio or theater.

P.S. Just thought of another possibility. A mildly loose or corroded connection could be contributing. You could have the power company come out to check their connections at the pole and weatherhead. You would need to hire an electrician to check your meter can and main panel, but it is probably not necessary unless you can see a problem at one of the lugs.
 
  #5  
Old 09-03-10, 09:57 AM
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Step one should be to eliminate any chance of an equipment problem as the culprit.

You could have a ground loop current causing the hum. Have you tried operating both subwoofer and HTS from the same point source, i.e the same outlet? http://en.wikipedia.org/wiki/Ground_loop_(electricity)

You can also temporarily break the ground on one or both pieces of equipment to check for a ground loop. If you do this, be aware that there could be a difference in potential between the two units. Measure first with a multimeter before touching.

Another option is to connect a separate ground wire between the two units. If your problem is a ground loop this will usually correct the problem. If you do this make sure the connection is short and solid - no alligator clips.
 
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Old 09-03-10, 09:59 AM
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Do the receiver and sub each have a 3 wire line cord? Since the sub will amplify 60Hz signals, you need to insure the rec and sub have their chassis at the same potential. Try running a #10wire to each chassis. I'd be surprised if ground rods, subpanels and power service is your issue.
 
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Old 09-03-10, 10:18 AM
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Thank you guys:

The subwoofer has been used at my previous residence with no hum whatsoever. I actually have multiple "subwoofers" (one a large tactile transducer) and both seperately amped, both impacted.

Since they both have dedicated outlets to the panel run at the same time in the same room, will a +/- of only a few feet of romex actually create a differential? I wouldn't think so?...

When I tried the cheater plug (break ground) on the sub it did not help. Note that the sub will hum independantly of being connected to the receiver in any way, and with or without 3rd prong connected, its not a signal differential issue. I actually broke the ground off the rca wire because it improves the situation not bonding the 2 through it


I should also add that I do know that multiple devices from multiple breakers cause the issue - any kind of heavy load. For ex. 1 Air conditioner is on older wiring but the kitchen has some newer dedicated wiring going to the house panel (wired correctly)
 
  #8  
Old 09-03-10, 03:29 PM
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You can try an audio isolation xformer. They're not too expensive and if the hum is on an audio line it might eliminate it.
 
  #9  
Old 09-03-10, 07:01 PM
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Originally Posted by tastyratz
Thank you guys:

Note that the sub will hum independantly of being connected to the receiver in any way, and with or without 3rd prong connected, its not a signal differential issue.
Is there hum with the input shorted out? That is, a shorting rca/phono plug? Is the speaker co-located with the amp?
 
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Old 09-03-10, 10:45 PM
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I know you mention many two plong receptales but what you will need to make sure the hot and netural conductor is not reversed if reversed sometime it will affect the audio equiment.

To test it you will need voltmeter and extendison cord and plug in to well verifyed grounded recetpale aka three slot receptale and run the voltmeter between the netural and hot and the cord ground to refered to see which one is netural due the three lamp plug tester will not work on two slots recetpale and normally if wired right the wider slot is netural while narrow one is hot.

If both are same size it will get little more tricky so this test will come in handy to verify it.

let us know if you can do it or not.

Merci.
Marc
 
  #11  
Old 09-04-10, 06:53 AM
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Hey Guys,
The hot and neutral are not reversed. hooking it all up to a single point outlet doesnt change a thing. rca ground looper wouldnt fly because the transducer needs a clean signal from 5-20hz where the transformer would shave and distort.

I started this thread because I needed to revisit a long time problem and when I gave it another look last night I realized my main sub is only a 2 prong plug (odd) but my transducer amp has a 3 prong. Going to a cheater plug and replacing a couple cables seems to have all but completely eliminated the hum.

The part that stinks? I dont like the idea of the cheater plug because its a 1000w amp, thats a lot of juice.
I would call the hum fixed but the concern for its potential still a flag for me.
 
  #12  
Old 09-05-10, 08:43 AM
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Based on your recent testing, an isolation transformer should help.

Standard Isolation Transformers

They aren't cheap (1000w is approx $260), especially since you won't know it works until you try it.

It's a safer solution to cheater plugs.
 
 

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