star grounding questions

[rocktavian]

yes running your grounds in the same raceway(conduit) should be fine. just dont put audio and electrical wiring in the same conduit. in fact audio and electrical should be separated by at least 12 inches and avoid running them parallel if possible.

as far as your star ground( we call it isolated ground) i am not so sure just running a separate ground from each outlet back to the panel and hooking it up with all the other grounds would do you any good. I personally wouldnt even call it isolated.

an isolated ground has its own isolated buss connected to its own isolated ground rod. this ground rod needs to be at least 10 feet from any other ground rod.

maybe i am way off base here but i find the isolated ground to be a little overkill. Is this going to be a full fledged commercial recording studio?

[copper]

right on...I have all the audio comming from the floor up throght the walls and all electrical coming from the poured cement cieling down the walls.

None of the Audio and Electrical share conduit nor run parallel. Some outlets do end about 12-14 inches away from a audio wall panel.

Non comercial at this point.

Running a new breaker box from the meter that will have only audio outlets connected and a seperate ground rod for the breaker Box.

All lighting will be connected to an exisiting breaker box.

thanks for the input!
John

[knightfly]

STOP EVERYTHING AND READ THE FOLLOWING -

Rocktavian, you need to read the NEC before giving advice on grounding - you may get someone KILLED otherwise. NO JOKE.

I normally don't cut and paste from info I've PAID for, for obvious reasons; but I'm going to make an exception here, just to CLEAR THIS UP and possibly SAVE LIVES - here is an excerpt from the NEC, pay particular attention to the LAST PARAGRAPH (in bold print) if the rest doesn't make sense to you -

250.6 Objectionable Current over Grounding Conductors.

(A) Arrangement to Prevent Objectionable Current. The grounding of electrical systems, circuit conductors, surge arresters, and conductive non–current-carrying materials and equipment shall be installed and arranged in a manner that will prevent objectionable current over the grounding conductors or grounding paths.

(B) Alterations to Stop Objectionable Current. If the use of multiple grounding connections results in objectionable current, one or more of the following alterations shall be permitted to be made, provided that the requirements of 250.4(A)(5) or 250.4(B)(4) are met:

(1) Discontinue one or more but not all of such grounding connections.

(2) Change the locations of the grounding connections.

(3) Interrupt the continuity of the conductor or conductive path interconnecting the grounding connections.

(4) Take other suitable remedial and approved action.

An increase in the use of electronic controls and computer equipment, which are sensitive to stray currents, has caused installation designers to look for ways to isolate electronic equipment from the effects of such stray circulating currents. Circulating currents on equipment grounding conductors, metal raceways, and building steel develop potential differences between ground and the neutral of electronic equipment.

A solution often recommended by inexperienced individuals is to isolate the electronic equipment from all other power equipment by disconnecting it from the power equipment ground. In this ill-conceived corrective action, the equipment grounding means is removed or nonmetallic spacers are installed in the metallic raceway system. The electronic equipment is then grounded to an earth ground isolated from the common power system ground. Isolating equipment in this manner creates a potential difference that is a shock hazard. The error is compounded because such isolation does not establish a low-impedance ground-fault return path to the power source, which is necessary to actuate the overcurrent protection device. Section 250.6(B) is not intended to allow disconnection of all power grounding connections to the electronic equipment. See also the commentary following 250.6(D).

End excerpt.

OK, once more - a STAR ground does NOT, NOT, NOT, mean that you eliminate continuity (connection) from your electronic gear to the main system ground - this is UNSAFE and, in most countries, ILLEGAL.

A STAR ground ONLY means that you have ONE, and ONLY one electrical path to ground for each and every source of electricity in the facility. The ONLY purpose of a STAR ground is to ELIMINATE the chance of ground LOOPS, which are the major source of hum in an installation.

The term, ISOLATED, when applied to a STAR grounding system, refers to special receptacles known as IGR - this stands for Isolated Ground Receptacle, and it means that the FRAME of the receptacle is NOT connected to the third, or GROUND, pin.

The main purpose of IGR's is in a CONDUIT system, because a conduit system requires that ALL METALLIC RACEWAYS (conduits) be BONDED to the earth ground.

If you do that, and you've used NORMAL receptacles, the FRAME of these receptacles (the part you screw to the outlet box) is BONDED to the GROUND terminal and therefore to the third hole in the receptacle.

This, in combination with the BONDED conduit system, means that now you have TWO paths for the ground from that receptacle - the WIRE you connected to the GREEN terminal which runs back to the system ground bar, and the BONDED CONDUIT system consisting of the outlet box, the conduit, and the breaker panel/system ground.

That will give you ground loops, because there are now two separate paths with a finite amount of resistance, which will act as an ANTENNA and pick up a small amount of line frequency, making your ground AT THE EQUIPMENT no longer ZERO VOLTS AC.

The proper way to wire these IGR's in a BONDED conduit system, is to BOND the frame of the IGR to the outlet box (you screw it to the box normally) - this provides the SAFETY ground for the system, which is now one continuous conductor thru the conduit and back to the breaker box and system ground.

Hot and neutral (black and white) wired the same as any other receptacle - may be looped thru to save wire, as long as you don't exceed # of outlets for wire/breaker size.

ISOLATED ground lug on the IGR receptacle - this runs to, and ONLY to, the MAIN SYSTEM GROUND (the one your heavy bare copper wire connects to, usually with copper ground rods driven into the ground - newer code requires a minimum 20 foot #4 rebar embedded into concrete slab (if there is one) and brought out of the concrete for a ground point.

What this all accomplishes is a technical power system with no ground LOOPS, but which is STILL SAFE and properly grounded.

Read this as many times as necessary to understand each section, and if you STILL have questions ASK THEM - this is, literally, a matter of LIFE AND DEATH. Don't stop until you are ABSOLUTELY POSITIVE you understand... Steve

[sharward]

Steve, thanks as always for helping us all maintain "not dead yet" status.

[rocktavian]

i understand what i was trying to say was that the extra grounding was maybe a little overkill for a closet studio. Most small time folks have had this same gear plugged into there normal garage and bedroom receptacles for months if not years. I just didnt see spending the extra time and $ on something not really needed. I am not saying by any means that you should eliminate the ground. I am just saying a normal wiring ( meeting code requirements) method would probably be sufficient for your standard Musiciansfriend recording studio setup. If ya got the time and money and knowledge then by all means do it full tilt.

I havent wired any Major Recording facilities but all my gear was made to plug right into a standard outlet.

I will not give out any more advice on wiring recording studios on this forum because it seems like i may be (umm whats the word im lookin for Construction Trash lol ) when it comes to the ins and outs of a recording studio.

I am just here to learn and i will leave the advice to the experts. Call me when ya need to add some lights to yer barn.

[drfrankencopter]

The star ground does not add "extra" grounding, all it does is ensure that each outlet has its own direct path back to the main household ground. By doing this, one bad apple (like a malfunctioning amp) will not spoil the tree (by making current flow in the ground through your other outlets thereby adding noise)! Is it worth the extra effort....I dunno, but if you have lots of gear on different outlets, its not too bad of an idea, and really an extra wire per outlet is not that much extra work now is it?

That said, how about muti-point stars? Do they meet code? Can I run a seperate ground wire from each recepticle box to an intermediate star point, and then buss that to household ground. This would be far more convenient for my installation...I can't see offhand how it could be any less safe than a conventional snaked ground, but I'm just a newbie at household wiring and don't know jack about the codes.

Cheers,

Kris

[knightfly]

Sure, there is no reason a star point has to be located right at the main system ground point; only that it's a star point, and that it's only ONE star point. IOW, the criteria is that ALL power sources in the studio have ONE COMMON grounding point, and only ONE path to GET to that point.

Here's a description of a proper grounding system for balanced power; but all the steps are also necessary for a NON-balanced power install where minimum noise is required -

http://www.equitech.com/support/techgrnd.html

HTH... Steve