Yet another Grounding Question-Separate 'Earth'


I emailed this question to Nsgarch since he gave advice on another thread respecting the separate grounding of a dedicated subpanel, but at the risk of making some of you read yet another grounding question, I decided to post it as well. Here goes:


My electrician has installed a separate subpanel for the audio system which is 'upstream' even of the main breaker panel in the house.
It will have several dedicated lines, each with a 20 amp breaker (Square D) running separate grounds to Hubbell Hospital Grade Outlets. I was concerned about the potential 'difference' among these separate lines- one will support mid-hi-freq. amps, others, the subwoofer amps, and a third, the lower powered front-end equipment (preamp, phono stage and TT- no digital). I do have one of those Granite Audio thingies which permits me to 'star ground' everything to a single point in the system, FWIW.
But, and here's the really critical question- my electrician has proposed a pair of separate ground rods about 10' from the main ground for the rest of the house electrical system, and in his view, the audio system subpanel would be grounded just to these new ground rods, not connected, by ground or anything else, to the rest of the house. In one of Nsgarch's postings on this subject, he indicated that there could be a differential in the two different panel groundings which could put current to the 'neutral' and create a shock risk. As I understood the advice, it was to make sure that the audio subpanel shares the same 'earth' ground as the rest of the house.
Could you comment?

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ADDITIONAL, not separate, grounds are a fine idea. IOW, adding ground stakes and attaching them to the new panel is fine as long as the new ground wire also runs to the old panel and adds to its grounding. My 1958-model house has an added 4g. ground wire running throughout the attic. It was attached to a waterpipe at the front of the house and the input panel at the side of the house. When I added 3 dedicated lines last year, the electrician added 2 ground stakes below the panel and grounded the already-grounded ground buss to these stakes. Yours should do the same. BTW I now water the bed of earth containing the new groundstakes about weekly, as I'm in the desert.
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I strongly suggest you check with the local building department or electrical inspector before you let this electrician do any work.

The subpanel is not a separate electrical source since it is in the same building as the service. Therefore it must be grounded at the point of the electrical source which is your main panel. Regardless if you put a separate ground rod for the subpanel, you MUST ground that subpanel back at the main panel. You cannot ground anything upstream of the main circuit breaker on its own ground. In other words, add all the ground rods you want, but you still need to ground back to the main panel.

What I suggest, and what I did in my house (which I do not want to burn down), is to install a 2-pole breaker in the main panel. Run wires from this breaker to your subpanel (no main breaker required in the subpanel). Run a separate neutral from the main panel neutral bus to the neutral bus of the subpanel. In the subpanel, install a separate ground bus. This ground bus MUST NOT be bonded to the subpanel or the subpanel neutral. Run a separate ground wire from the subpanel ground bus all the way back to the main panel and join it to the ground at that point. Connect your dedicated circuit grounds to the subpanel ground bus and the dedicated neutrals to the subpanel neutral. This is effective and legal.

You cannot ground seperately, unless your jurisdiction permits it. The reason for the ground is to trip circuit breakers, as the ground becomes an "escape hatch" for short circuit current in the event of a fault. By using separate or multiple grounds, the possibility exists that a short circuit may be routed away from the breaker, causing a dangerous situation.
If the ground wire is only connected to a ground rod or an underground metal or copper water pipe, the circuit breaker usually will not trip if there is a short to ground. There has to be a connection to the neutral from the ground to trip the breaker. Power from the hot wire goes to ground and then to the neutral to trip a breaker in a ground fault. A sub panel does not have the neutral and the ground connected (bonded) together, the main panel does. If there was a ground fault or a short circuit on one of the circuits in the sub panel and there was two seperate grounding systems for each panel this is what will happen. The power will go to the sub panel ground rod and try to go through the earth and make a connection to the main panel ground rod which is connected to the neutral so the breaker will trip. You can not use the earth as a grounding conductor. The main neutral wire from the street makes the breaker trip and not the ground. Thats the reason that all grounds have to be connected together so the fault can go to the neutral and trip the breaker.
>>"But, and here's the really critical question- my electrician has proposed a pair of separate ground rods about 10' from the main ground for the rest of the house electrical system, and in his view, the audio system subpanel would be grounded just to these new ground rods, not connected, by ground or anything else, to the rest of the house."<<
>>>>>>>>>>>
Find another Electrician! You may want to ask what else he is doing that does not meet NEC and your local codes.

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Gs5556's post is right from the text book, NEC. Follow his post and you will meet NEC code.
The earth shall not be considered as an effective ground-fault current path back to the source.
Whart, what is the problem (power, safety or audible) that you are trying to cure? Why do you need a separate panel? Maybe there is a simpler way.

>>By using separate or multiple grounds, the possibility exists that a short circuit may be routed away from the breaker, causing a dangerous situation.<< Only the hot side of the circut is fed through the breaker, so multiple paths back to the panel are immaterial. The current has already been through the breaker and cannot be routed away. The ground wire itself is a separate path, parallel to the neutral.

I do agree that not connecting new grounds to the exsiting panel or connecting the subpanel neutral to ground anywhere but the main panel are REALLY BAD IDEAS.

Let's talk about the underlying problem and try not to create new ones.



Many thanks to all of you, and to Nsgarch, for the timely responses. Work will be done by the book, according to Code and to Hoyle. The balanced power idea is also intriguing. I will let you know how it goes and will scream if I have questions in the midst of it. Thanks again, everybody.
Whart, glad to hear you will not be using a separate equipment grounding conductor and ground rods for the sub panel that does not connect back to the main electrical service panel grounding electrode system.
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>>"My electrician has installed a separate subpanel for the audio system which is 'upstream' even of the main breaker panel in the house."<<
>>>>>>>>>>>>

Just curious how did the electrician do this? Did he tap into the Hot conductor/s ahead of the main breaker, of the main service electrical panel? What size is the main 2 pole breaker, 100 amp, 200 amp? Did he install a new breaker and enclosure at this tapped location to protect the feeder that runs to the new sub panel? How did he connect to the neutral conductor ahead of the main service panel? How far is the sub panel from the main electrical panel? What size of wire did he install to the new sub panel? How many conductors, wires?
I hadn't been down to the basement to look at his work- here's what we have right now: a Square D subpanel is feeding off the main panel, fed by a metal insulated cable that appears to be close to an inch in diameter. No further work has been done (yet)- he will return later this week. I suspect that when he said he wired this panel in, 'upstream' of the existing box, he really meant upstream of all the existing breakers, perhaps, save for the main power breaker on the incoming service.
The ground wire out of the main box is a massive thing, looks like its multistrand, also probably an inch thick, wrapped in a light grey, rubber-type insulator.

I'll make sure I discuss these postings with him. He has done good work for us in the past, and is pretty meticulous. Perhaps he didn't mean that the ground to the subpanel would be totally isolated, and that the panel wouldn't also grounded to the main house system, but I sure heard it that way.
As to problems I'm trying to solve, well...

The room in which the hi-fi exists is already overcrowded with other equipment for the video system. My preference would be to install the audio only system in another room, but at least for now, that's not possible.
I'm pretty fanatical about the noise level in the system, and have tried myriad ways so far to reduce the noise level at idle. (As mentioned in another post, an industry guy who I respect for his technical knowledge heard the system a couple weeks ago, and scoffed at my complaint that the system was noisy).
In any event, the video system is powered by its own dedicated 240v stepdown transformer. That in turn handles the power for the various 'audio for video' amps and also supplies the juice to a big Richard Grey box which powers the projector, line doubler, and small signal video stuff.

I want the audio system totally isolated from that, and I'm moving the audio equipment (other than the speakers) to another area of the room --partly to get it away from my ears, and partly because the compressor for the Air Line arm can then be stashed in its own little room, isolated from the listening environment.

In doing this, I just want to make sure I have the best possible AC feeding the system. The current demands made by the system are modest. While I am currently using Shunyata Hydras, I'd also like to hook up without them, and see what the difference is. At present, the other outlets in the room are not 'dedicated' and are part of the standard electrical system that was installed in the room about 5-6 years ago, when the upper floors of the house were substantially renovated.
ps- house has 200 amp service, all upgraded about 5-6 years ago when the house was massively upgraded by the prior owner.
Whart,
>>"house has 200 amp service."<<
>>>>>>

I assume the 200 amp main breaker shares the same panel enclosure as the branch circuit breakers. Is that correct?
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>>"fed by a metal insulated cable that appears to be close to an inch in diameter."<<
>>>>>>>>>>

From your description the wiring assembly is MC cable. 1" in diameter, probably 4 #6awg THHN conductors. Maybe 5 conductors if the MC is Hospital Grade. I am just assuming the sub panel will be a 120/240 volt panel. 2 Hot conductors, 1 neutral conductor and 1 equipment grounding conductor. Wire ampacity rating of 60 amps.
Is that correct?
At the main electrical panel, the electrician will install a 2pole 60 amp breaker for overcurrent/short circuit protection for the new sub panel feeder and sub panel bus bars. The 2 conductors of the MC cable, usually black and red, intended for the 2 Hot conductors will connect to the 2pole 60A breaker. The white (neutral) and green (equipment grounding conductor) will both connect to the neutral/ground bar. At the sub panel the neutral conductor will connect to the isolated neutral bar and the equipment grounding conductor to a separate ground bar bonded to the panel enclosure.

What type of branch circuit wiring will the electrician be installing? What brand of receptacles are you going to use?
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EMI noise.
Just curious why are you not just installing another isolation transformer with electrostatic shielding and a new panel to feed your audio equipment branch circuits. Usually a sub panel is installed because of a lack of spare breaker spaces in the main electrical panel or the audio branch circuits conductor are very long and ground loop problems exist.
OK, not to add to the confusion, but to answer the questions:

We have 200 amp service, goes into a main panel with one big breaker, littered with all kinds of smaller 15 and 20 amp breakers (box is quite full), and an existing subpanel that appears to be set up for some of the kitchen appliances.
The new subpanel is a 100 amp box, set up right now with 3 Square D 20 amp breakers. I'll check to see if he installed a 60 amp breaker in the main panel to support this new subpanel.

It was my intention to have him set up a number of 20 amp dedicated lines from this new subpanel, strictly for the audio-only system, and rather than have him ground the receptacles at each wall box, to run separate ground wires back to the subpanel for each- not daisy chaining the receptacles to each other. I have ordinarily used Hubbell Hospital Grade receptacles- only because of habit, and because i know Bill Hubbell, and figure his trust fund needs the money (He is a serious car junkie).

The run from the panels up to the room is easily 75-100 ft., depending on routing.
The only reason I hadn't considered another transformer for this system is that the one currently used in the video system is located in the room, inside one of the Mid-Atlantic racks, and I can hear it hum at idle, when all the video equipment is shut off. (When the video system is on, the fan noise masks that). I suppose one could set up an isolation transformer down in the basement, near the panels, but would that defeat the purpose if the outputs of the transformer then have to make that long run? Apologies in advance for my ignorance.
OK, went back down and checked- no new 60 amp breaker that I can see in the main panel, to support the new subpanel. Is it possible that the subpanel is wired as if an 'extension' of the main panel, and that he fed it, and its array of 20amp breakers from the main panel, but before any of the other breakers (other than say, the monster one at the top of the panel?) This would explain his statement about setting it up 'upstream' of the existing breakers (sic).
Obviously, I will ask him when I ring him tomorrow. He won't be back to my house until mid-week, so I'm sure I can get the skinny from him, and let you know as we proceed. Thanks to all so far, and particularly to JEA 48 for all your follow up on this. Regards, Bill Hart
>>"It was my intention to have him set up a number of 20 amp dedicated lines from this new subpanel, strictly for the audio-only system, and rather than have him ground the receptacles at each wall box, to run separate ground wires back to the subpanel for each- not daisy chaining the receptacles to each other. I have ordinarily used Hubbell Hospital Grade receptacles"<<

New audio branch circuits should be dedicated circuits. Each with its own Hot, neutral, and equipment grounding conductors.

Nothing wrong with Hubbell Hosp grade receptacles. Just make sure they are the HBL8200H (15A) or HBL8300H (20A) type. Note the "H", that means non nickel plated. Hey do me a favor. When you speak to Mr. Hubbell will you confirm the gutts inside the 15A and 20A recepts are identical. And only the face plates are different to be in compliance with UL and NEC? I contend the gutts are the same, 20 amp rating.
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>>"The run from the panels up to the room is easily 75-100 ft., depending on routing."<<
>>>>>>

That would explain the new feeder and sub panel. The smallest wire I would of used is #3awg copper. If the electrician is indeed using #6awg, jmho, it ain't big enough, not for the distance for audio gear.
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>>"The only reason I hadn't considered another transformer for this system is that the one currently used in the video system is located in the room, inside one of the Mid-Atlantic racks, and I can hear it hum at idle, when all the video equipment is shut off."<<
>>>>>>>>>>

What manufacture is it? Is there possibly a midway point, or closer, to the audio equipment where the xfmr could be installed?
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>>" (When the video system is on, the fan noise masks that). I suppose one could set up an isolation transformer down in the basement, near the panels, but would that defeat the purpose if the outputs of the transformer then have to make that long run? Apologies in advance for my ignorance"<<
>>>>>>>>>

Not ignorance at all. Your logic makes sense. If it had to be in the basement, by the main electrical panel, imo it would just need to be a little larger, more KVA. Kind of like a bigger battery.
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>>"OK, went back down and checked- no new 60 amp breaker that I can see in the main panel, to support the new subpanel. Is it possible that the subpanel is wired as if an 'extension' of the main panel, and that he fed it, and its array of 20amp breakers from the main panel, but before any of the other breakers (other than say, the monster one at the top of the panel?) This would explain his statement about setting it up 'upstream' of the existing breakers (sic)."<<
>>>>>>>>>>>

Maybe he has not installed it yet. Or maybe you missed it. The breaker and wire could be larger than #6 with a 60A breaker. Just make sure one is installed after the the 200A main.
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Email this Audiogon member, Cincy_bob , he installed a 7.5 KVA Topaz xfmr with electrostatic shielding a while back . Ask him if his is noisey. I am sure he can give you some pointers.
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Jim
Whart,
How about an update. What did you end up with?
Jim
OK, here's the scoop: Richie, the electrician, completed the wiring of the new outlets to the room, as follows (BTW, I printed out this thread for him to read, and apart from a few questions about his competence, he explained to me why what he did met Code and was otherwise kosher): the 3 20 amp circuits are wired to the subpanel using #10 wire and each has a separate ground back to the subpanel. The subpanel ties into the main board at the 200amp breaker, but before any of the other breakers in the main panel. It shares the same ground as the main panel, but has an additional ground to earth in proximity to the house grounding rod. The subpanel is protected by its own 60 amp breaker, which then feeds the three 20 amp circuits. The subpanel is mounted adjacent to the main panel.
Since local supply houses did not have the Hubbell receptacles on hand, I bought a bunch of Porter's tweaked Hubbell receptacles.
Now, for the punchline. Perhaps a little less noise than when hooked up to the regular house outlets, but still suffering some grounding noise issues. Prior to installation of this new electrical subsystem, my best result was obtained by deriving all system power from the same set of outlets.(Remember, I don't draw a huge amount of current with this system).
Obviously, once I 'cheat' everything but the preamp, the grounding noise goes away, but I am still reluctant for safety reasons to lift the grounds on any of the equipment.

I have achieved quietude right now with the following arrangement- the Duo bass amps remain grounded through the 3 pin cord (Shunyata) plugged into a Hydra 2 which goes (with 3 pins) into one of the three new dedicated lines. (Each speaker has its own Hydra 2/Shunyata cord array, fully grounded, plugged into its own wall outlet right behind the speaker- both 'speaker ac' receptacles are on the same dedicated line- call that dedicated line "3").

The Lamm L2 line stage is plugged directly into the wall on dedicated circuit 2, no cheater. Ditto, the Steelhead phono preamp. Floating the ground of the STeelhead or not makes no discernible difference, so I have not cheated it.
The Audiopaxes are plugged into a Hydra 4/Anaconda which goes into dedicated circuit #1. Here, to get rid of the hum, I have to lift the ground on the amp cords going into the Hydra 4. (The Hydra 4 is using all 3 pins into the wall at dedicated circuit # 1 but viewing the Hydra as simply a wall receptacle extension, the amps really aren't
'grounded.')
I also tried plugging the Hydra 4/Audiopaxes (no cheater on the amp cords) into dedicated circuit #2, which powers the Lamm line stage, and no improvement.
I have hooked up the Granite Audio Ground Zero product, and have separate ground lines from the Duo amps, the Audiopaxes(cheated, as above), and the Steelhead all converging at the Ground Zero device. With some experimentation, this yielded a relatively quiet, hum free system, but if I ground the Ground Zero to a wall socket, using the supplied 'dummy' 3 pin plug, the hum is back.
For safety reasons, I'd still prefer to be able to avoid any cheaters. To sum up, right now, the only cheated plugs are on the Audiopax amps. (I assume that unplugging the Hydra 4 from the wall when I am not using the system makes no difference for safety purposes, since the amps are still connected to the rest of the system via the interconnect and speaker cables).
So, if you've hung in with me so far, it seems that there is almost no way around lifing the ground in this system somewhere to make it noise free. The grounding problem is an 'intercomponent' grounding difference, and not a bad ground from the wall. The grounding differential appears to be between the Audiopax amps and the amps in the subwoofers.
The only thing I didn't try was to also hook up the Duo subwoofer amps to the same dedicated circuit as the front end electronics- I could try that, which would mean the whole system is running on one 20 amp circuit- probably not a problem from a current draw perspective, but it would mean , if that worked, that I would have to have Richie rewire the outlets now on circuit 3 to tie into circuit 2 instead- I will test this temporarily before having him do that. It also means that having multiple dedicated lines for the same system is pointless, given the grounding differential between the circuits.(And, to the extent there is some subtle benefit to having more current on hand, despite the modest demands of my system, I am losing the benefit of that by forcing everything to feed off one 20 amp line).
With sincere apologies for the length of this post, I invite any thoughts or suggestions (:)!
oops> One last thought. Preamp fully grounded. Ground lifted on Audiopaxes. But, both components have separate ground wires to the Ground Zero device. Does this mean that the amps are effectively grounded via the preamp? Is that true even though the various connections on the Ground Zero are 'buffered' from one another?( ie, the Ground zero allows separate ground connections that interact with each other thru multiple position 'impedence' switches).
And, note that the Ground Zero is not itself separately grounded since if I plug its dummy ac plug into a wall outlet, the hum comes back.
Just to add to the confusion.:)
Whart,
You called your new dedicated branch circuits 1, 2 & 3. Is your new sub panel a 120/240 volt panel? Or is it a straight 120 volt panel? Does your circuit numbers match the factory breaker numbers on the panel front cover? If the sub panel is 120/240V are all the dedicated circuits on the same line, L1 or L2, in the sub panel but not one on one Line and the other two on the other Line? Audio equipment that is connected together by wire signal carrying ics should be fed from the same line. If not, this can be a source of noise.

For another source of noise, have you ever checked the AC plug orientation for the proper AC polarity of the primary side of the power transformers of the Amps and preamp? You will need a decent multimeter and a pair of tin snips. The snips, you will need to trim the wide blade on one of your ground cheaters. It will need to be trimmed enough so it will plug in either way into the electrical receptacle, outlet. If the ground cheater is the pigtail equipment grounding conductor type tape off the bare lug on the end. If it is the type with the metal equipment grounding strap either cut it off or tape it so it cannot touch the receptacle cover plate mounting screw. The screw is grounded.

Start with one of the Amps. The Amp must be totally isolated from the grounding system, of your electrical system. Disconnect the ics from it and the preamp. Plug the amp into the modified cheater plug and plug the cheater into the wall outlet. Turn on the amp. Set your multimeter to AC volts. Insert one of the test lead probes into the wall outlet ground hole, make sure you make good contact with the ground contact. Touch the other test lead probe to the back chassis of the amp. If the back is painted remove one of the screws and touch the probe to the bare threaded area of the chassis. You should now show an AC voltage on the meter. Write down this voltage measurement. Turn off the amp. Unplug the ground cheater and rotate it 180 degrees and plug the cheater back into the outlet. Wait a couple of minutes to let the caps in the amp to bleed off. Now turn the amp on. Connect the multimeter test probes in the same manner as before. Note the voltage reading. The **lowest reading** of the two readings is the correct AC polarity, phase relationship, for the primary winding of the power transformer of the Amp. If the plug orientation is correct the lowest AC voltage reading measured, the wider polarized blade of the plug for the Amp will match that of the neutral contact of the receptacle, (20 amp recept T slot).

Repeat the same test procedure for the other amp/s and the preamp.

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