Electrical Panel Grounding


Beyond electrical code requirements, why does the sub panel earth ground, with its own earth ground, need to be tied to the main electrical panel ground?
wgutz
All grounds must be bonded together at the service panel. This is for safety reasons, and to ensure that breakers will trip properly under fault.
Is the sub panel in the same building as the main panel or is it in an unattached garage?

What do you mean "with its own earth ground"? You cannot -- in the same building -- run a separate grounding conductor from a sub panel to a location other than where the house service is grounded. If there is a grounding conductor from a sub panel to, say, a water pipe that is more than 5 feet where the water pipe enters the house, the house water piping could be energized in the event of a fault. 

The sub panel must have a ground bar that is bonded to the sub panel and the circuit grounds get attached to the bar. That ground bar must be bonded to the main service panel ground at the point of entry by either a separate wire or metallic conduit to the sub panel from the main panel.

The sub panel must have an isolated neutral bus that prevents the sub panel circuit neutrals from being grounded upstream of the service panel, resulting in neutral currents raising the potential on the sub panel metallic parts and ground.

If the sub panel is in an unattached building and fed from a breaker in the main panel, then the sub panel needs its own earth ground (to a ground rod) and does not need a grounding conductor to the main panel.  
Earth "grounds" at different physical locations can have several volts of difference in potential. Depends on lots of factors. Only way to ensure it is at 0 Volts relative to AC is to tie them together. :)

Also, important, while you may have multiple grounds tied together, and even loop them, you may ONLY tie the neutral and ground together at one place, the service entrance. The service panel does not necessarily equal main. :)
So, the plan was to put a half dozen copper clad ground rods outside in the earth and run 6 separate ground leads to the sub panel. This should allow for an easier electrical noise pathway by lowering potential. If I connect this ground field back to the service panel, then I will connect with the noise from other home electrical devices, such as dimmers, etc. What I'm reading above is that 1) A separate ground field may cause breakers to not activate correctly and 2) cause a differential neutral voltage. I'm not clear on why multiple ground fields only makes sense for a separate building.

The sub panel powers primarily the stereo, but my neighborhood electrical is really noisy until about 10 PM. I do use PS Audio power regenerators, one on the front end and one on the amps. But they can't handle all the noise. 

So, does anyone have a different opinion on what appears to be good advice above? And I do appreciate you guys taking the time to try and teach me some power grounding fundamentals. But I am a slow learner.
Wguts, none of this is necessary nor will it improve anything.

What matters is that it all be referenced to a single point, where the neutral is bonded to it. Putting in a single, or 20 ground rods won’t help this at all.  Follow the NEC, and local codes which may now require 2 rods.

I’d focus on your room acoustics. :)

The point of the ground is to act as an earth safety, which it can only do well if bonded to the neutral at 1 location.

Now if you want to run isolated grounds from the panel, that's fine.

Thanks Eric:

As an audiophile, we have had success in the past with using a ground field (multiple ground rods). My associates include a satellite engineer who made the original suggestion. I believe I have a audiophile grade system. I am using Sounlab U-2 electrostatics driven by 6C33C power tubes.

Since you brought up room treatments, I work on this every weekend. One question you may know the answer to is regarding 2" square wood block diffusion panels. While using longer pieces of 4" and 5" I understand this will increase the octaves covered over 1", 2" & 3". But what discernible sound effect would this have? it sounds to me as is there is some additional blurring in the mid-range.My focus is to tame some high frequency hardness.
High frequency hardness can be caused by local RF affecting signal via unshielded ICs and speaker cable (think Kimber, Nordost).
The earth does not possess some magical mystical power that sucks nasties from an audio system.

The main purpose for an electrical service connection to earth is for lightning protection.

You can fill your whole yard with driven ground rods if you like as long as they are all tied together and connect to one point to the main electrical service entrance neutral conductor.

NEC Code says the equipment grounding conductor for a sub panel shall installed in the same raceway, conduit, or cable assembly, as the feeder conductors feeding the sub panel.

The purpose of equipment grounding grounding conductor is provide a low resistance path for ground fault current to return to the source in the event of a ground fault event. THE EARTH IS NOT A LOW RESISTANCE PATH . When a sub panel is used the source is the main electrical service panel where the sub panel feeder equipment grounding conductor is connected to the service entrance neutral conductor. IF the ground fault current is greater than the breaker handle rating the branch circuit breaker in the sub panel will trip open breaking the ground fault circuit. IF the ground fault current leakage, due to a high resistance in the ground fault circuit, the circuit breaker in the sub panel just sees the ground fault current as connected load.

NEC code does allow an auxiliary grounding electrode to be connected to the equipment ground bar in a sub panel in addition to the feeder equipment grounding conductor.
IN ADDITION TO. NOT IN PLACE OF. I would not recommend it though. Lightning will travel through any path provided from the earth back to the earth. Especially a low resistance path.

Here is a great white paper for you to read.
https://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf

wgutz,

A mix of diffusion and absorption is always a good thing!

High frequency hardness is a funny thing. While a lot of people focus on 1st  and 2nd reflections, this can also be treated by generally adding absorption in the room. In other words, some of the problems are due to direct reflections, but some are just doe to how slowly or quickly it takes signals to decay.

You can experiment cheaply with throw rugs/blankets and putting other soft, absorbent materials on the walls. If that takes you where you want to go, then you are going in the right direction.  Also, don't neglect the ceiling!

You may also experiment with toeing speakers outwards so you are not in the direct line of fire of the tweeter.
Eric - thanks fro the input.

Hair(;o
Jea - I read the article, and there is a bit fro me to learn. Thanks for your trouble to forward the link.
Jea - I read the article, and there is a bit fro me to learn. Thanks for your trouble to forward the link.
I should have mentioned you only need to read about the first 36 to 38 pages of the white paper.

I also should have asked you, in my last post, what country do you live in?  Earth ground is earth ground the world round but how it is accomplished/done/required varies. My comments are for the USA.

Here is a video on the subject of the use of an Auxiliary Grounding Electrode. It really serves no purpose and can cause damage to electronic equipment if used in the event of a nearby lightning storm.

https://www.youtube.com/watch?v=WlnFNTay-9Q

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Jea - that youtube is exactly what I needed to know. This forum is amazingly helpful because a handful of people, like you, care enough to share.

I live in Denver with my wife, Lori. My system consists of a custom built pre-amp using two B29 tubes and two small front end Mullards. It is with transformer or OTL switchable circuitry, and switchable capacitance so I can tune to the source.
CD's need less and Vinyl more.

The amps are custom made with two 6C33C tubes per monoblock, 4 Mullards for the ancillary functions and a fairly massive output transformer. Class A/B with a solid 60W per side and 5 separate transformers for the various required voltages.

These amps are plenty to power my Soundlab U-2s. I prefer the U-2s 6' x 3' size over its larger brethren. These have been modified is several ways not easy to explain.

All running Audioquest cables, mostly silver over copper. I know that is way more than you asked, but I somehow thought you might find it interesting. One day I do a post on the pictures/system page, as the room is covered with my own acoustic diffusion and absorption panels which were sized and located by ear and trial and error. If you ever want to build your own, I do have some useful tips that will save you from learning the hard way like I did. And they work better than any of the stuff I tried that was made commercially at about 1/10th the cost.


wgutz ,

Thanks for your informative response.

The reason I asked in an earlier post what country you live in is because when I checked your profile, country was listed as N/A. You might want to change that to USA.

Now that I know you live in the US I have a few questions for you regarding the AC power delivery system used to feed your audio equipment.

What manufacture of sub panel are you using? Copper or aluminum bus?

Feeder size wiring feeding the sub panel?

Sub Panel wired 120/240V?

Approximate length of dedicated branch circuit wiring from the sub panel to the receptacle outlets feeding the audio equipment? (Up down and all around)

Type of branch circuit wiring used?
Example:
2 wire with ground NM-B cable? (Romex is a trade name). If romex how was the cabling ran through joists and or wall studs? Though a common bored hole or individually bored holes? If separate bored holes how far apart were the holes apart from one another? There in Romex cables kept separated from one another.

3 conductor MC armor cable? Aluminum or steel armor?

Conduit with wire loosely pulled into the conduit? If this wiring method was used was a separate conduit used for each 120V dedicated branch circuit?

Are all the dedicated circuits fed from the same line, leg, from the sub panel that feeds audio equipment that is connected together by wire interconnects? All fed from Line 1 or all from Line 2. (Not from Line 1 and Line 2.)

What are you using for wall outlet duplex receptacles? Manufacture, style and or series number? Plated contacts? Type of plating?
What material is the supporting back strap made of? Steel? Brass, other?

What are you using for cover plates for the wall duplex outlet receptacles?
Plastic? Flexible nylon? Stainless Steel? Other?

All the above can have an impact on the sound of your audio system.
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I have learned to appreciate the need for the one point of neutral tie in at the service panel and the tie to ground for lightening. And why the grounds must be tied together for safety,

One theory that lurks is; if all electric power seeks to return to the source, what is that source for the harmonic distortion and noise created by say a neighbors refrigerator or a faulty relay. And what about the energy used in powering a motor. That energy is not returning to the source. And why does the power get so quiet when it is really wet (rain) outside? These are my questions with my thinking that ground may have some influence as the "sump" theory goes. My local friend advocates a ground field of a half-dozen copper clad rods, each with a separate ground wire tie back to the main panel to lower ground resistance. He is a satellite engineer for the railroad, and is personally working on some changes to basic sigma-delta class D technology, so I do have some respect for his opinions.  

My outlets are PS Audio Blaun (sp?) that replace normal outlets with a double box, and have a machined aluminum face plate. They feed into twin PS Audio power regeneration units (one on the front-end and one for the power amps). The feed is not currently from the existing sub-panel and the sub-panel only feeds a set of outdoor receptacles powering the pond and water features that I can completely turn off during listening. So the plan is in formulation. And the sub-panel may need to be redone altogether.  I would only use lager gauge copper wire to create a dedicated audio feed. And historically, I used a metal (wound style) shield for the wiring from the sub-panel to the outlets, I bought my home with the existing wiring in place.

One oddity, at least to me, is that the existing sub-panel has the power take-off from the main panel by using two 20A breakers in the main panel. Both the main and sub-panel are less than 20' from the audio outlets.I always thought you just came off the main bus for sub-panel power.

I look forward to hearing your input.


wgutz,

The lower the Grounding Electrode, ( example, ground rod), to soil resistance the better. IEEE recommends 5 ohms or less, preferably 2 ohms or less.

It’s not the number of ground rods driven into the earth that will necessarily yield a 2 ohm soil resistance. A lot depends on the content/type of soil and soil moisture. Where you live can make a difference. The 4 seasons can greatly impact soil moisture. It is possible a single 5/8" X 20ft driven ground rod will have a lower ground resistance than 6 individual 5/8" X 8ft driven ground rods.

When multiple ground rods are driven into the earth they should all be tied/connected together with a single wire extended and connected to the electrical service entrance neutral conductor. The multiple ground rods then become a single Grounding Electrode.

Harmonics? The earth will not reduce harmonics.

The majority of harmonic noise found on the AC mains in a home are caused by electronic devices found in the home. Seldom will those produced in the neighbor’s house end up adding to the harmonic noise found in your house.


A refrigerator motor does not produce harmonic noise. Now the micro processor that controls the features on the refrigerator can.

Nonlinear loads produce harmonic noise back on the AC mains.
Examples of,

Switch mode power supplies
Light dimmers
Hair dryers
Computers
Variable frequency drive units found on many of the furnaces built today. (Controls blower motor speed)
Dual wattage portable electric space heaters.
CFL and LED lights
Electronic ballasts

//

PS Audio power regeneration units.

Curious, have you ever checked if the outputs of the two units are in phase with one another? If you have a multi meter measure the voltage from the hot contact from one of the output receptacles on one units to the hot contact of an output receptacle on the other unit. If the outputs of the two units are in phase you should measure zero volts nominal. If out of phase you will measure 240Vac nominal.

//

Sub Panel.

Don’t use it to feed your audio equipment. The wire feeding the panel is too small. Use the main electrical panel.

http://www.p3-inc.com/images/grounding_for_pq_wp2016_p3.pdf
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Testing soil resistivity

http://www.fluke.com/fluke/iden/solutions/earthground/soil-resistivity-method

Thanks for the info. I'll test the phase of my PS units when I have them close enough for my test leads.  

I have thought of pouring a concrete pier say 6' deep and 12" diameter mixing the concrete with an additive for conductivity. Do you know if graphite would work? I once knew but have since forgotten the correct additive.

There was an electrical testing facility here that dug out the entire parking lot about 12' deep and put in a conductive 4' thick conductive concrete pad full of rebar all tied together with what looked like bronze or copper clamps. It was at least 300' by 300' in size. I guess they wanted a low resistance ground.

Bill
I have thought of pouring a concrete pier say 6’ deep and 12" diameter mixing the concrete with an additive for conductivity.
I assume inside the concrete you would install at least #4 re-bar, copper wire/s, or a ground rod.

6ft is not very deep. Bare minimum for a ground rod per NEC code is 8ft. Again bare minimum. As a rule a single 8ft rod will not achieve a 5 ohm or less ground resistance even in good fertile farm soil.

What is the make up of soil like in Denver? How about on your property? Is it rocky and sandy? What is the average yearly moisture content in the soil? What is the resistivity of the soil?

How about the summer months. How much rain fall is there? How moist will the soil be from the surface of the earth to 6ft down? What will be the soil resistance of the soil all the way around your concrete encased grounding electrode? How many feet out in all directions around the grounding electrode? If the resistance is high, say above 5 ohms what good were all your efforts? It is possible the soil resistance could be 100 ohms more or less.

Is the soil corrosive? If yes that can determine what metal is used for an electrode.

If you are serious about supplementing the electrical grounding electrode system of the electrical service of your house I would suggest you hire a power quality expert from Denver that can test the soil resistance. He will be the best qualified to recommend best practices for your area. You may have to first start with a commercial/industrial electrical contractor.

It is possible the grounding electrode system you have now is adequate. It may need to be inspected for loose and or corroded connections. Do not do this yourself. Hire a qualified licensed electrical contractor.

Here is some more reading reading material for you.

https://www.engineereducators.com/docs/groundingandbonding2-2.pdf

http://www.cpccorp.com/deep.htm

I ran across this picture several years ago. I still get a laugh seeing it.
http://i.imgur.com/rbAo0Vc.jpg
Thanks - you are correct. I will hire a real expert. Bill