500 Series chassis ground vs circuit ground in bussed star ground configuration

[jdurango]

I'm wiring grounds to the busbar in my studio which will utilize a bussed star scheme. Grounds have been lifted where appropriate (hopefully!) at the patchbay, and my plan now is to install ground lift plugs on all gear in the control room, including my console, which redirects the chassis ground to my busbar, which will connect directly to water mains.

Firstly, is this advisable? (using ground lift plugs to redirect chassis ground)

Secondly, my 500 series rack (Radial Workhorse 8 with mixer) has 2 screw terminals on the back, labeled "chassis" and "circuit". Of course these are shorted to one another somewhere internally. So what is the best way to connect my 500 series rack to this setup?

1) Use the ground lift off the PSU cable to redirect ground @ socket end to busbar as with everything else?

2) Use ground lift plug + attach a single copper wire to each terminal and then to the busbar? I'm afraid this would create a ground loop....but so would a single copper wire shorted to both (as it's also shorted somewhere internally).

3) Perhaps just a single wire from one of them? If so, which one is preferable?

4) Other option?

Thanks!

Jonny

 

[radardoug]

The safety ground is there for a reason. Safety. Ground lifting all your a.c. cords is a big nono. Also by doing so you will void any insurance you might have.
In a professional studio using balanced interconnects, there is absolutely no reason to lose the mains ground.
Lift cable shields where necessary. If in a high rf environment, use caps on those lifts to bypass the rf to ground.
Where you have unbalanced signals, look closely at how you are interfacing. Generally, unbalanced to balanced will work fine, transformers will always work fine, balanced to unbalanced can be tricky. Consider balancing any unblanced inputs.

 

[jdurango]

The safety ground is there for a reason. Safety. Ground lifting all your a.c. cords is a big nono. Also by doing so you will void any insurance you might have.
In a professional studio using balanced interconnects, there is absolutely no reason to lose the mains ground.
Lift cable shields where necessary. If in a high rf environment, use caps on those lifts to bypass the rf to ground.
Where you have unbalanced signals, look closely at how you are interfacing. Generally, unbalanced to balanced will work fine, transformers will always work fine, balanced to unbalanced can be tricky. Consider balancing any unblanced inputs.

To be clear I'm not proposing lifting the mains grounds. Ground lifts at the patchbay are only for curcuit/shield and will always be connected on the other end for RFI blocking. Also this was NOT done on mic/tie lines which will be grounded on both ends.

This scheme is commonly utilized to provide a more ideal "0 potential" ground than via AC mains....the chassis ground is lifted from the wall plug/AC junction box but diverted to a ground strap, then to a water main pipe. I believe the main advantages are that you can provide a better ground connection than typical AC mains wiring offers, and offer only one path to ground as everything must go through the busbar since circuit ground is lifted at the patchbay.

I just wanted to avoid ground loops between circuit/signal ground and chassis ground. Just noticed my GML 8302 has the same feature (symbols for chassis and circuit ground) but they are shorted with bare wire on the outside of the unit as stock from the factory. I'm guessing I should do the same with the 500 rack then.

 

[Brian Roth]

Hi Jonny.  From your description it sounds like you propose to use "3 prong to 2 prong Cheaters" on the AC power plugs.

Lord knows I've done some of that over the decades but I'm not proud of my actions.

The round third pin (USA style) is there as a safety grounding connection.  Lifting that pin may or may NOT "fix" a noise problem, but you are entering into  a Twilight Zone of likely safety issues that violate Electrical and Insurance regulations.

Beyond that, your water pipe connection has to be bonded to the grounding point at the breaker panel to comply with the electrical code.....city/electric code/insurance specs.

And.......in this day and age......while you MAY see a metal water pipe, there is no assurance it's actually connected to a solid ground because so much of the water piping system now relies on PVC plastic.

What I suggest is a properly designed and installed (not rocket science) Isolated "hospital ground" outlets  all fed from the same phase leg at the breaker panel.

Don't cheap out and try to recycle old funky wiring in the building.  Build it up from new.

Bri

 

[jdurango]

Hi Jonny.  From your description it sounds like you propose to use "3 prong to 2 prong Cheaters" on the AC power plugs.

Lord knows I've done some of that over the decades but I'm not proud of my actions.

The round third pin (USA style) is there as a safety grounding connection.  Lifting that pin may or may NOT "fix" a noise problem, but you are entering into  a Twilight Zone of likely safety issues that violate Electrical and Insurance regulations.

Beyond that, your water pipe connection has to be bonded to the grounding point at the breaker panel to comply with the electrical code.....city/electric code/insurance specs.

And.......in this day and age......while you MAY see a metal water pipe, there is no assurance it's actually connected to a solid ground because so much of the water piping system now relies on PVC plastic.

What I suggest is a properly designed and installed (not rocket science) Isolated "hospital ground" outlets  all fed from the same phase leg at the breaker panel.

Don't cheap out and try to recycle old funky wiring in the building.  Build it up from new.

Bri

Hey Brian,

The building I'm in is a super old warehouse built around the turn of the century (the last one). Not only is the electrical not amazing, I'm certain the main pipes are all metal throughout (although I could check with the building engineer). Also, there happens to be a main water distro on the other side of the wall of my control room. Would only need about a 30 foot run from the bus bar.

I guess I'm not clear on how people implement star chassis grounding. I thought the whole point was to have all the grounds at the bus bar (hence the "star").....if I do this, but also keep the third prong connected at the AC outlet, that's an obvious ground loop. How would it be unsafe to simply move the ground from the outlet to a ground rod or water main? The connection is still grounded, likely much better than before, just direct to a huge copper bar out via a short run of thick copper wire to a water main or ground rod instead of via the outlet > thin little 12ga wire to a sub-panel > panel > utility > grounding rod.

How is the latter better or safer than the former?

 

[radardoug]

It doesn't matter what you think is safe. Its what UL and the insurance companies think. Also, could there be a situation where you removed your ground and left mains power on the unit? Thats not safe.
To repeat, in a well designed studio, there is NO reason to remove the mains ground.

 

[PRR]

I've had to ground-lift maybe 0.1% of all the audio power cords I've ever plugged in.

Leave everything wall-grounded. Have one or two (at most) 3/2pin cheaters but do NOT use them except after all else fails. Good studio gear will be fine that way. AND SAFE.

 

[jdurango]

Okay, I understand it's against code. But can someone please help me understand how to implement a star chassis/bussed ground scheme without creating obvious ground loops then?

Star chassis/bussed grounds is a common scheme, it was recommended by my tech (one of the best in the PNW) and the "grounding gurus" he consulted with, as well as my console manufacturer.

My console is wired into the new PB exactly the same as stock, with some grounds "lifted" at PB, others connected at PB. All mic/tie lines have grounds connected and NOT bussed.

Other than that, ALL external gear has it's ground lifted ONLY at the patchbay (connected on the "gear end", thus providing a shield).

My understanding is that the entire point of star chassis grounding scheme is to provide ONE AND ONLY ONE PATH TO GROUND.

Can someone please explain how to implement this then, if you have one path to ground via AC mains, plus another path through the patchbay, into a ground plate, then either back to AC mains, or to a water pipe or stake in the ground or whatever? It seems like that would completely defeat the point of a star chassis scheme.

And with all due respect, I don't find the argument "it's wrong/unsafe because code says it's wrong/unsafe" to be compelling. I'll deal with the implications of safety and code myself and work that out with my electrician. Again, with all due respect, I'm not asking for advice about code, I'm asking for audio technical advice.

My question is, how is one supposed to implement a star chassis ground scheme if there are multiple paths to ground (ie via crappy 100 year old AC mains connection through multiple pieces of gear including the console + through a ground plate hooked potentially to an entirely different/much stronger ground source....or even back to the same AC mains)? This seems like a perfect recipe for a ground loop with two very different potentials. If AC mains ground MUST be connected, why would anyone use this system at all??

Thanks fellas!

 

[abbey road d enfer]

My understanding is that the entire point of star chassis grounding scheme is to provide ONE AND ONLY ONE PATH TO GROUND.

OK, I understand that, however what are supposed to be the practical properties of such an implementation?

Can someone please explain how to implement this then, if you have one path to ground via AC mains, plus another path through the patchbay, into a ground plate, then either back to AC mains, or to a water pipe or stake in the ground or whatever? It seems like that would completely defeat the point of a star chassis scheme.

You seem to imply that this "star chassis" thing has magical properties, and that failing to fulfill is doomed.
Thousands of studios, concert halls, conference rooms... are testimony that multiple grounding and "ground loops" do not necessarily impair performance, as long as certain rules are obeyed. The actual recommandation from the AES promotes ground loops! Indeed there are issues with equipment that fails to follow the rules, as many vintage units do, particularly those where the ground pin of I/O connectors is tied to the analog "ground" instead of the chassis ground. Indeed, most unbalanced equipment is a challenge in this respect.
I have been quite often confronted with these problems and have always found a solution and never have resorted to a ground-lifted plus, except for troubleshooting.
Having a well thought-out and solid earth distro is essential.

 

[jdurango]

OK, I understand that, however what are supposed to be the practical properties of such an implementation?

Besides the added safety inherent to a good solid ground, lower noise floor and more stable operation in all equipment, especially digital.

You seem to imply that this "star chassis" thing has magical properties, and that failing to fulfill is doomed.

I'm sorry if that's how it's coming across, but that is not my implication. I'm simply saying there is a reason for star grounding (ie. to provide ONE path to ground) and there are best practices to accomplish this, and those best practices are not based on magic or some crazy idea, but EE 101....and creating two paths to ground with very different potentials seems like it defeats the entire purpose (ie to eliminate ground loops and thus greatly decrease, but not eliminate the potential for problems).

"Star Ground - A type of grounding scheme used in some studios to prevent ground loops. It requires isolating each piece of gear from AC ground (using a ground lift adapter) and running a separate ground wire from the chassis of each piece (including the racks themselves) back to the main studio ground (we call this “Technical Earth”). This “Tech Earth” gets connected back to a main AC ground, and/or a large copper rod driven 18 feet into the ground. Thus every piece of gear still has AC fault protection, but no earth grounds are tied together. Technically limited ground loops can still exist in the studio signal wiring, but the path length differences are minimized to an extent that it isn’t likely to be a problem. Star Grounding is a time consuming and complex wiring scheme, but is generally very effective at preventing ground loops and works great in conjunction with other measures such as telescoping shields. Occasionally you’ll still find some piece of gear that requires audio transformers to eliminate ground loops. Generally you’ll find that with today’s equipment, you really don’t have to go as far as all this. Telescoping shields, balanced lines, and careful consideration to signal cable wiring with today’s equipment is often good enough."
https://www.sweetwater.com/insync/star-ground/

This is exactly what I'm proposing, only with a water or sprinkler main instead of ground rod, which isn't feasible in my scenario. It should also be noted I'm using a lot of oldschool gear, mostly 60's and 70's stuff (tape machines, console, old tube equipment, etc.) in addition to some modern digital equipment.

Thousands of studios, concert halls, conference rooms... are testimony that multiple grounding and "ground loops" do not necessarily impair performance, as long as certain rules are obeyed. The actual recommandation from the AES promotes ground loops! Indeed there are issues with equipment that fails to follow the rules, as many vintage units do, particularly those where the ground pin of I/O connectors is tied to the analog "ground" instead of the chassis ground. Indeed, most unbalanced equipment is a challenge in this respect.
I have been quite often confronted with these problems and have always found a solution and never have resorted to a ground-lifted plus, except for troubleshooting.
Having a well thought-out and solid earth distro is essential.

I understand that some venues, concert halls, studios, etc. will run into ground loops, especially in larger spaces which need to use multiple circuits, possibly even multiple panels where it's not always feasible to run ground wires hundreds or thousands of feet to a single point for a proper star ground scheme. So of course, they must design around this and probably won't implement such a grounding scheme, or if they do, will have to make compromises. My situation is nothing like this. My entire studio is about 3,000 square feet, and the control room, server closet, power supply/"rack room" and tape machine room all share a wall with each other and all of the equipment to be grounded will require no more than 15 feet of wire to get to the busbar. Beyond that, the install notes for my console recommend a star ground configuration. The entire studio has been designed around this system. I was simply asking in the OP how to hookup a single piece of gear (which has separate connections for chassis and circuit ground).

I'm unable to find an AES paper on how to implement star grounding. If you're referring  to a paper on some other grounding scheme, that may be the case, but I'm not implementing some other grounding scheme, and I'm certainly not redesigning my studio. My tech and I along with more specialized consultants have decided on star chassis grounding with bussed ground on the patchbay (again, except for tie lines). We have settled on this for a number of reasons, I'm just trying to implement it as best as I can without paying a tech to answer simple questions like this.

Guess I'll figure it out myself or shoot the tech an email and see if he can help. We've already spent a ton of money, and right when we were getting ready to open up, this COVID crap hit us hard....can't afford to pay someone to sort this out.

 

[abbey road d enfer]

OK, so, in contradiction with regulations, you have decided to implement a scheme that has very little substance.
Star ground is justified for safety. As opposed to daisy-chain earth, a default in one of the sockets affects only the apparatus that is connected to it.
Now in terms of noise optimization, using star ground implies  great lengths of earth wire that are potentially developing parasitic voltages. By opposition, hierarchic ground presents smaller lengths of wire, hence less differential voltage between "grounds".
Since you are set on this decision, I won't try to convince you, but I'm sorry, I can't help you find the "better way" of doing what I wouldn't choose to do myself.
The Sweetwater article describes what a star ground scheme is, but fails to prove it has superior quality. The AES (Muncy et al.) have long since proved that the receipe is somewhere else. Check "Pin 1 problem". Between Sweetwater and the AES, there's no contest.

 

[jdurango]

OK, so, in contradiction with regulations, you have decided to implement a scheme that has very little substance.
Star ground is justified for safety. As opposed to daisy-chain earth, a default in one of the sockets affects only the apparatus that is connected to it.
Now in terms of noise optimization, using star ground implies  great lengths of earth wire that are potentially developing parasitic voltages. By opposition, hierarchic ground presents smaller lengths of wire, hence less differential voltage between "grounds".
Since you are set on this decision, I won't try to convince you, but I'm sorry, I can't help you find the "better way" of doing what I wouldn't choose to do myself.
The Sweetwater article describes what a star ground scheme is, but fails to prove it has superior quality. The AES (Muncy et al.) have long since proved that the receipe is somewhere else. Check "Pin 1 problem". Between Sweetwater and the AES, there's no contest.

Again, no ground wire will be more than 15 feet, most will be under 5 and wired direct to a copper busbar with a short run of heavy 6AWG wire to a water mains. How is that more prone to parasitic voltage than long runs of wire through multiple junction boxes to a panel, then through utilities in a 100 year old warehouse, out to the street and finally to utility ground?

What AES describes is one method of grounding, not the only one, and not the best in every situation. My console manufacturer, tech and grounding specialists we consulted recommended another.  Again, I'm not here to second guess the entire design of my studio or get into an argument about the merits of star grounding vs others with someone who isn't even familiar with the particulars of my studio. I was simply looking for advice on hooking up one piece of gear.  Guess I'll try elsewhere. Thanks anyways!