Star Grounding System Question

[Hi Def]

Awesome - I think I got it now! Off to Home Depot to get the supplies! Once again, Bryan, Thank you for all of your help. This board and the people here are a tremendous help.

All the best,
M

[cfuehrer]

I am not trying to be double trouble, but I read through the other forum posting and all of the info here. Bryan, could put in one posting EXACTLY what should be done. I would be driving my electrician nuts and charge me more if I just handed him all these printed posts and told him to figure it out. I also want to know exactly what to do incase I need to troubleshoot or feel I can handle some of the install work. Thanks!

[giles117]

My Assumption (maybe from reading to fast) was that he was doing this himslef, However if he has an electrician, then all he needs to do is give the guy the star grounding diagram and tell him to isolate the studio electrics grounds from the other grounds.

I actually took the electricians Test back in 94, and if you dont understand basic circuit design well you might not make it past page 1. LOL

[Aaronw]

Here's another link that briefly covered some isolated circuit info:

http://johnlsayers.com/phpBB2/viewtopic.php?t=1330

[knightfly]

You're allowed 40% fill on FMC (Flexible Metal Conduit) when pulling more than two wires - the tables and rules involved are so lengthy that I don't want to post half of the NEC here so people can figure this out - if anyone has a specific case, please post your wire size and type, total # of conductors, and conduit type (FMC, EMT, Rigid, etc) and I'll look up all the relevant tables and calculate conduit size for you... Steve

[bigdaddyd]

Can I throw in 2 cents. I wont try to 'one up' any of your advice, but being an electrical contractor and reading these posts, I'd like to point out one area of concern that may be misunderstood...

A ground's first concern is safety. Any grounded parts (metal bodies.. intermal, external, etc) must be grounded so when electrified by mistake or wiring failure, an overcurrent device(breaker) will trip. First and main objective.

Metal conduit is a perfect way to run circuits, and as far as I know the NEC and most city jurisdictions allow the conduit to act as the ground. And like posted before, a simple ground screw in the back of any metal box can have a lead attached and hooked to an outlet. There is your ground.

The nice thing about conduit is you can pull another ground,(usually a green piece of THHN insulated wire) and have it totally isolated from the ground that is supplied by the conduit. Run it back to the service panel and its isolated. Whala- an isolated ground.

This is harder to do with romex, as your cable has one ground wire and cannot be isolated if it is used to ground any metal bodies like metal boxes, so a separate piece of green wire must be ran and isolated. I have no valid input on how to do this best to reduce ground loop and such. not my area. BUT......

The area of concern is this... you can not install a ground rod only on an equipment ground and have a safe means to properly "Ground" anything. a ground rod is supplimentary and is added to a grounding system. Again, the best way design a ground rod into a system for recording is not yet my area, but I wanted to make sure that noone just hooks up a ground rod and nothing else and figures that would trip a breaker in the event of a fault in the circuit.

[Aaronw]

Here's a link that describes some of the theory behind STAR GROUNDING.

http://svconline.com/news/avinstall_tec ... index.html

And some more interesting info on grounding...

http://www.engineeringharmonics.com/papers/s_vc.htm

[giles117]

In reference to Big daddyd's comments.....

This is specifically why I recommend a seprate breaker panel JUST for your Studio Electronics. Most, if not all utilities will run you a separate meter for this purpose (and of course bill you accordingly. )

And to add this one little detail that Aaron so graciously provided for us.

The entire technical ground systems of conductors and ground busses is insulated and isolated from all other systems with the exception of a single point at the centre of the ground system that must be, by electrical code requirements, connected to the other grounding systems within a facility.

Just make sure this one minor detail is properly observed.

[Aaronw]

And if you really got the budget, and want to have good isolation, then we can venture into the world of BALANCED power.

[knightfly]

Bigdaddy brings up a point that may have gotten lost - a star ground system is NOT designed to BYPASS any electrical code that is meant to provide SAFETY - only to SUPPLEMENT a standard install in such a way as to make sure there is only ONE common ground point for equipment, not a DIFFERENT ground point.

The code does indeed state that metal boxes will be grounded and bonded, and this is a safety concern. If a hot wire somehow either melts or gets skinned, etc, and contacts the metal parts that humans can touch, if that metal part isn't already grounded this could become a LETHAL situation. Grounding of all metal parts ensures that if the above happens, then overcurrent protection (fuses or breakers) will operate, removing the danger and alerting us to the fact that there's a PROBLEM.

For safety, this is fine - for QUIET electronics, it isn't enough. If equipment gets its ground from different points along the same grounding conductor, and ANY small amount of current is allowed to flow in that conductor, there will be a voltage drop (albiet small) - any difference in voltage will cause a current flow, and now we have noise induced into anything that's handy.

To avoid this possibility WITHOUT voiding the safety aspect, the ground that each piece of gear sees must be at exactly the same potential as the ground for every OTHER piece of gear; otherwise, when we hook grounded shielded audio cables between gear we now have a LOOP which makes current flow possible between units, hence NOISE.

The way we satisfy BOTH safety and quiet power is relatively simple, although anyone reading the code book for the first 2000 times could argue otherwise - we first satisfy safety - all metal parts of the wiring system grounded to the main system ground. Period. For a system using METAL conduit and metal boxes, this presents a problem for technical power grounding - standard electrical outlets have their metal parts which screw into the metal box BONDED to the ground pin in the outlet - so any gear plugged into this outlet would have its ground/chassis grounded to the system ground. If each receptacle gets its ground from the common ground system, and also has its cabling grounded to other chassis, there is the potential for a LOOP, which means current can flow, which means NOISE.

To get away from this, and still satisfy safety, we need to make sure each piece of gear has a solid ground that is at the exact same potential as every OTHER piece of gear. This means NO LOOPS, and can only be done by running each piece of gear's ground from a common point, with no chance of a loop.

If using metal conduit and boxes LEGALLY, this system requires that there be no bonding of ground within the receptacle, but WITHOUT eliminating the safety of EVERYTHING being grounded. This is accomplished by using IGR's, or Isolated Ground Receptacles -

Under this method, safety ground of the wiring system itself is done in normal fashion - but the safety ground for the GEAR is ONLY connected through the ground pin of the receptacle, which is ONLY connected to the COMMON STAR GROUND - this way, each piece of gear's chassis is tied to the EXACT SAME POTENTIAL so there is no chance of current flowing in the ground.

To continue this "quiet quest" to completion, you should also NOT use metal racks unless using individual ground isolator tabs on each piece of rack mounted gear - optionally, use wood racks and rails, preferably with threaded metal inserts for durability. This keeps individual rack pieces from forming their own ground loop.

With all that out of the way, I'll try to write one paragraph that applies to each wiring method -

ALL METAL SYSTEM -

If using metal conduit and metal boxes, the receptacles MUST be of the IGR type. Mount the receptacles in the boxes normally, the conduit will be bonded to the boxes, this entire system will be bonded to the building ground, and this completes the safety ground to code. Since this is a conduit system, you'll be using separate wires and NOT romex - the STAR ground part now needs a separate (green) INSULATED wire that runs ONLY from the ground lug on each receptacle, back to the STAR point, which must be bonded to building ground. If you have 15 duplex outlets in this system, EACH outlet must have its own separate insulated green wire that ONLY connects to the outlet's ground terminal at one end, and directly to the STAR point at the other end.

Now, when you plug a piece of gear into the wall, its chassis is connected directly to the STAR point, which is at building ground potential, but does NOT have any possibility of a LOOP - therefore, every piece of rack gear is at the same potential so when you connect audio cables there will be no current flowing in the ground.

ADDED STIPULATION - code requires ALL conductors (including all grounds) to be in the same conduit for a given supply, because the mutual inductance of the wires is part of what trips safety equipment (breakers) in the event of a ground fault.

METAL BOXES, WIRED WITH ROMEX - This presents a slightly different problem - now, we have metal boxes (which must be grounded for safety, same as above) but no conduit to ground them to. For this sytem, we STILL need the IGR outlets to accomplish a STAR system - each metal box will use the ground wire included in the ROMEX for its safety ground - this wire is bare, and will be connected to the box at one end and to the ground buss in the panel at the other end; daisy-chaining these box grounds is fine, because they are NOT part of the STAR system.

To provide the STAR system, we must connect each receptacle's ISOLATED ground lug through an INSULATED ground wire back to ONLY the common STAR point.

Now comes the "glitch" - because of the code requirement that ALL wires for a circuit be run in close proximity (I'm still looking for the exact wording of this, but it IS part of the code) this means you can't run the separate STAR ground wires just anywhere - they must be close to, and parallel to, the current carrying conductors of the romex. Our bud in Colorado ran into this, and satisfied the inspector by using FMC run through the same holes in studs as the romex, with all STAR ground wires in the FMC.

Finally, if receptacle boxes are PLASTIC, and we're using ROMEX, the ONLY change is that IGR's are not necessary - because the boxes are plastic, there is no grounding requirement for the boxes.

This leaves TWO possibilities for wiring - one is to do a "home run" for each and every outlet, each receptacle gets its own romex. The ground connects to the frame of the receptacle, you make sure a second receptacle in the box doesn't touch its neighbor, and the romex ground ONLY connects to the receptacle ground at the box and to the STAR point (which is bonded to system ground) at the panel.

The second way would allow daisy-chaining of the romex conductors between plastic outlet boxes, EXCEPT that it would require a SEPARATE, INSULATED, ground wire to be run from each receptacle in each box straight to the STAR point; still no IGR's required as long as multiple receptacles in a box do NOT TOUCH each other. This isn't hard to do, just a caution that it's necessary. The downside of this is the hassle of having to run all the romex runs in the same set of holes through studs, PLUS that pesky FMC full of separate, INSULATED, star ground wires.

This is why the simplest (maybe not quite the cheapest) way for star grounding with plastic boxes is the first one.

Electrically, the graphic posted by Bryan is the one to go by - hopefully my long-winded explanation above will help figure out HOW you can accomplish this, and it's all in one place - if more gets added that I may have omitted, I can edit this post to include it - eventually, we can add it to the stickies here so it's easier to locate... Steve

PS - when I finally find the code language for the "proximity of ground conductors" thing, I'll add that too -

[Aaronw]

Thank you Steve for clearing up several of the issues. Great thread. I'm posting this as a Sticky now... Lots of good info...

[bigdaddyd]

One way to satisfy the "romex" problem is to run your circuit in a 12/3 or 14/3 ( preferabley 12 though) and hook black to power, white to common, ground to ground, and use the left over red for your ISO ground. Phase tape it green on both ends. This ground will be braided through the romex with the rest of the wires in a spiral. I dont know If that will effect any thing.

The code states that all grounds must terminate together in a box, Unless in the event of an ISO ground, in which case you should for sure spend the $12 or whatever for the correct ISo ground outlets,

I HAVE A QUESTION. How important is it for all the outlets on a star system to be the same distance from the common splice. Is this even a factor? Or are we creating a system where the ground has only one isolated path back to the main system, and eleminating the possibility of picking up ANY other ground interferance on the way. Is that it?!? If so that makes sense and is more of a simple concept than I had originally thought.

One other thing. the authorities in my area allow an isolated ground to be pulled with romex and stapled with romex and thats it. We have used #12 THHN solid. But isolated grounds have usually been a requirement spec'd out by engeneers, and most installs of that calibur - IE; commercial, industrial, hospitals, big recording studios, are run in conduit, so the extra ground gets pulled in there with everything else.

g

[knightfly]

Great call on using 12/3 with ground - this would mandate a "home run" for each receptacle, but still a great way to satisfy ALL requirements -

Distance from the common splice, or STAR point, is irrelevant because, as you said, there is only ONE path for the ground from each receptacle, so no chance of a loop. With zero current flow, basic theory states that there will be no difference in potential. This is similar to using a telescoping shield in audio wiring... Steve

[giles117]

Great Info Big Daddy

[knightfly]

Oh, for all non-electricians out there - the term "phase taping" refers to a practice that's code-acceptable, where you use a different colored wire than its iriginal intended purpose - to do this, you must use colored tape at each end of the conductor to identify the wire's purpose; IE, green for ground... Steve