Best Grounding for 200a panel.

Hello all.

I am installing a 200a 3ph sub panel in a venue to power audio amplifiers. This audio equipment will have it's own isolated ground. The client said he want's 3 grounding rods. Is there any reson 3 rods will serve better than two?

thx
 

infinity

Moderator
Staff member
The number of ground rods won't matter much. Is this in a separate structure? And how do you intend to connect the IG to the system? You cannot connect it solely to the ground rods.
 

Dale001289

Senior Member
Hello all.

I am installing a 200a 3ph sub panel in a venue to power audio amplifiers. This audio equipment will have it's own isolated ground. The client said he want's 3 grounding rods. Is there any reson 3 rods will serve better than two?

thx
Not really. ‘Triad grounding’ (i.e. 3 triangulated ground rods separated by 10 feet) is not a code requirement but more of a common practice for some industries. The intent typically is to reduce ‘noise’ or EMI, i.e. ‘electromagnetic interference’ within control systems circuity such as analog, communications etc. One of the buried rods is usually designated as a grounding test well, which allows periodic testing of the system for resistance – the lower the ohms, the better. You’ll have to bond the Isolated Grounding system to the ‘dirty’ or safety grounding system in at least one point – and this is a code requirement.
 

roger

Moderator
Staff member
As the others have mentioned, the new ground rods from this new sub-panel will still have to be connected to the existing grounding electrode system. Isolated equipment grounding does not mean isolated earthing.

Roger
 

zbang

Senior Member
This audio equipment will have it's own isolated ground. The client said he want's 3 grounding rods. Is there any reason 3 rods will serve better than two?
You can charge extra for installing it.

Is this for temporary or permanent audio systems? With the latter, they have a prayer of it staying isolated for at least a few weeks; with the former each event is a toss-up.

If you search these forums, you find that most people here don't have a high opinion of IG systems.
 
Let me explain further. The Isolated portion is intended for a couple 4 wire 50 amp distro outlets for the stage. The band will connect their portable distribution panel to these outlets. The objective is absolutely to reduce noise. There are many old school bands that will be using old style transformer based ampliers for sound.

So to redirect, would there be a way to completely isolate these (2) 50 amp 4 wire outlets from the "dirty" system and if not will would a still be a benefit to using seperate ground rods.
 

roger

Moderator
Staff member
Let me explain further. The Isolated portion is intended for a couple 4 wire 50 amp distro outlets for the stage. The band will connect their portable distribution panel to these outlets. The objective is absolutely to reduce noise. There are many old school bands that will be using old style transformer based ampliers for sound.

So to redirect, would there be a way to completely isolate these (2) 50 amp 4 wire outlets from the "dirty" system and if not will would a still be a benefit to using seperate ground rods.
The bottom line is the grounding has to all be connected period, no compromise.

Forget the ground rods and run a isolated EGC straight to the first point of service, that's all you can do legally.

You do understand that the earth does not clear a fault or provide personnel protection at the voltages you are working with don't you?

Roger
 

infinity

Moderator
Staff member
If you're thinking that somehow ground rods are the solution to a potential noise problem you're incorrect. It's dangerous and because of that connecting solely to the rods is not permitted by the NEC. The EGC from your 50 amp receptacles must be connected to the system EGC. As Roger suggested the best you can do is run an IG back to the service or if there is one a transformer X0 connection.
 

zbang

Senior Member
So to redirect, would there be a way to completely isolate these (2) 50 amp 4 wire outlets from the "dirty" system and if not will would a still be a benefit to using seperate ground rods.
Sure, install a transformer and supply the outlets from a separately-derived-system; that'll isolate the power leads from the "dirty" power system. No matter what you do, the outlets' grounding conductor has to run back to the system bonding jumper and to the grounding electrode system; and if you add a second set of ground rods, those must connect back to the main set (it's all in Art. 250). You have to provide a path for fault current and also to the GES.

What the client is looking for is an audiophile-induced snake oil solution. If you want to really get into the weeds, technically, take a look at http://web.mit.edu/jhawk/tmp/p/EST016_Ground_Loops_handout.pdf, the author knows his business.
 
The bottom line is the grounding has to all be connected period, no compromise.

Forget the ground rods and run a isolated EGC straight to the first point of service, that's all you can do legally.

You do understand that the earth does not clear a fault or provide personnel protection at the voltages you are working with don't you?

Roger
Yes of course Roger. I just have little experience with isolated systems. Thats why i am asking.
 

tom baker

First Chief Moderator
Staff member
Using separate ground rods was very common (and dangerous) 25 years ago with serial connected computers, each computer had a different reference and that caused issues. The solution (and dangerous) was to lift the equipment ground (green wire)
If you lift the green wire or do what you have proposed, if an amp has a short to the case, the little electrons want to go back to the source via the disconnected green wire. When someone touches the amp, they complete the circuit and can easily be electrocuted.
Section 250.6 (D) Was added many code cycles ago:
Limitations to Permissible Alterations. The provisions of this section shall not be considered as permitting electronic
equipment from being operated on ac systems or branch circuits that are not connected to an equipment grounding
conductor as required by this article. Currents that introduce noise or data errors in electronic equipment shall not be
considered the objectionable currents addressed in this section.
 

kwired

Electron manager
Yes of course Roger. I just have little experience with isolated systems. Thats why i am asking.
Isolated grounding basically means you isolate the EGC from other components all the way back to the service equipment or other common point, but it is still bonded to the EGC and GES at or near that point.
 

cuba_pete

Senior Member
Isolated grounding basically means you isolate the EGC from other components all the way back to the service equipment or other common point, but it is still bonded to the EGC and GES at or near that point.
I've been working with "isolated ground" systems for 30+ years (or so people think).

I have gotten away from that expression and replaced it with Single-Point Ground (which is what it really is) in curriculum and literature to alleviate the confusion that some still have with specific bonding and grounding methods.

I wish they had never used the IG designation for receptacles. Either way IG is a receptacle, not a system.
 

kwired

Electron manager
I've been working with "isolated ground" systems for 30+ years (or so people think).

I have gotten away from that expression and replaced it with Single-Point Ground (which is what it really is) in curriculum and literature to alleviate the confusion that some still have with specific bonding and grounding methods.

I wish they had never used the IG designation for receptacles. Either way IG is a receptacle, not a system.
Single point is what is intentionally grounded. Without intentional isolating, you still have other points that may be a non intentional grounding point.

Steel raceways in steel framed building - you have grounding naturally occurring all throughout the facility even though you may only have limited points that are intended for "grounding" of the electrical system.

Even if you pull EGC's through non metallic conduits - you bond them to items that may have a ground reference.

Pull an "isolated grounding conductor" and attache it to an item that has a metal frame and is in contact with building steel or other grounded objects, you sort of don't really have an isolated ground anymore.
 

cuba_pete

Senior Member
Single point is what is intentionally grounded. Without intentional isolating, you still have other points that may be a non intentional grounding point.

Steel raceways in steel framed building - you have grounding naturally occurring all throughout the facility even though you may only have limited points that are intended for "grounding" of the electrical system.

Even if you pull EGC's through non metallic conduits - you bond them to items that may have a ground reference.

Pull an "isolated grounding conductor" and attache it to an item that has a metal frame and is in contact with building steel or other grounded objects, you sort of don't really have an isolated ground anymore.
It's a lot of work making sure there aren't unintentional grounds.

That's one of my primary jobs. My facility is less than 100,000 square feet, and only a portion uses single point grounding methods. I just have to keep my head on a swivel, make daily checks and supervise all installs well.
 

jaggedben

Senior Member
As the others have mentioned, the new ground rods from this new sub-panel will still have to be connected to the existing grounding electrode system. Isolated equipment grounding does not mean isolated earthing.

Roger
Are these not auxiliary ground rods that don't have to be bonded to the GES?
 

roger

Moderator
Staff member
Are these not auxiliary ground rods that don't have to be bonded to the GES?
The way I'm reading the OP is that they want to have a stand alone GES, but regardless, even if they are "auxilaiary rods per 250.54 (take note of the last sentence) they would be connected to the EGC which is connected to the building GES so they would be common to the original system anyways.

Roger
 
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