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
« Last Edit: March 20, 2020, 10:46:20 PM by jdurango »


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.

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.
« Last Edit: March 21, 2020, 12:13:23 AM by jdurango »

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



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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.


 

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