Star Grounding System Question

Ian, a separate, dedicated ground (but bonded to other ground system, which is MANDATORY) will probably give slightly better noise floor, but with or without you'd still see the least amount of noise when ALL your gear sees one common ground point - this is true, even if you're on the 27th floor of a building and are tied to a ground bus wire that runs all the way from the basement. The main thing is that (a) there is only ONE ground point, and (2) only one PATH to that point from any piece of gear. Note that I'm not saying this would be AS GOOD as being on the ground floor with a heavy, short wire running directly to a proper ground electrode - odds are it's NOT. But the single point for every item in your studio to get its ground will ALWAYS be better than several separate runs to a remote point. Hence the comments elsewhere about telescoping shields, isolated chassis, etc - the minute you have more than ONE WAY to get to the ground, you have a LOOP (spelled A-N-T-E-N-N-A...) Steve

Steve, Thanks a lot for this. I will see with my electrician what I can do and will make sure I do a Start Grounding system even if I must connect it to the main grounding pipe anyway, the good thing is that that main pipe goes through my garage before going into the groud. I simply have to make sure it is at least 3m into the ground. But how could I install a balanced power system ? Thanks Alex

knightfly wrote:

Ian, a separate, dedicated ground (but bonded to other ground system, which is MANDATORY) will probably give slightly better noise floor, but with or without you'd still see the least amount of noise when ALL your gear sees one common ground point - this is true, even if you're on the 27th floor of a building and are tied to a ground bus wire that runs all the way from the basement. The main thing is that (a) there is only ONE ground point, and (2) only one PATH to that point from any piece of gear.Steve

Thanks Steve, that's what I hoped. Star-earthing it shall be ! Ian

Balanced power - these are the guys who were instrumental in getting balanced power added to NEC a few years ago - http://www.equitech.com/ check out their FAQ and white papers, there's a LOT of info there... Steve

Being a dumb-computer guy and not an electrician, I am trying hard to reconcile this sticky with what has been proposed for my basement. Here's the scenario... the house has a sub-panel located in the basement that is a 40 amp service off of the main panel. There will not be any air-conditioners, stoves, fridges, dryers etc on the sub-panel, but they are connected to the main panel. The electrician (in talking to him about noise) has said that "what he's always done is run isolated ground outlets with homeruns back to the panel". He suggests I find out which outlets in particular in the studio I want isolated, as to cut down on wire cost (because he can daisy chain the rest). I am assuming that the isolate ground outlets in essence acts the same as the star ground because they would all share the same ground point (the grounding strip on the sub-panel) and would from there be bonded to the ground of the main panel which is required by code. My thought is to run homeruns for everything because you never know which outlet you might suddenly need for audio.. but maybe I'm too paranoid. What do you think? Does this sound like he is approaching it correctly or is there something I'm missing altogether? Thanks, Jim (Velvet Elvis)

He has the right idea; IGR outlets are what's needed to do a proper star ground system, especially if it's run in metal conduit (conduits are supposed to be BONDED to the ground system, so a standard outlet in a metal box/metal conduit run can NOT be isolated - the FRAME of a standard receptacle is bonded to the ground terminal so the third prong of your plug would automatically be grounded to the conduit and earth, which makes it NON-isolated ground. The IGR receptacles SEPARATE the third pin of the plug from FRAME ground, so a separate wire can be attached to the isolated ground terminal of the receptacle and run back to your common star point without creating a LOOP. IGR's require 4 separate wires because of this - Hot, Neutral, Safety ground and Isolated ground - the Hot, Neutral and Safety grounds CAN be daisy-chained if on the same breaker, but the Isolated grounds must ONLY be connected to the common Star Point, regardless of where this star point is located. This is what makes the IGR's work - each ground pin of each receptacle has only ONE PATH to a COMMON point, so ALL of these isolated grounds are at EXACTLY the same potential because there is no (reasonable) chance of current flow in that isolated ground wire. If you're running everything with Romex, and your boxes are plastic, then standard receptacles are OK - but this gets a bit tricky unless you go with 3-wire plus ground Romex and do home runs for EACH OUTLET back to your common star point, because code requires that any SEPARATE ground wires be run "in close proximity" to the other wires, and "protected" which can get interpreted by some inspectors to mean "conduit" - The "close proximity" thing is to ensure that a dead short will trip the breaker quickly, and has to do with inductive coupling of all the wires involved - if your separate ground is running a different physical path back to the panel, this inductive coupling doesn't happen and a short can conceivably take too long to trip the breaker, increasing the possibility of a fire. I'm of the same mind as you are; in a studio, there's a chance that ANY outlet could be used to power gear so I tend to make them ALL the same; same star ground, SAME PHASE. Dedicated lighting and other stuff can be put on the OTHER phase of your service to help balance loads. I personally don't think "penny-wise and pound foolish" makes sense, especially when you'd have to destroy a sound-isolated wall to get at the wiring when you find out you shoulda done it better... Steve

Steve, It is all plastic boxes... so there will not be any conduit. I'm confused about the 4 wires needed when using plastic boxes. Where does the 4th wire go, as the standard outlets I've seen have connections for hot, nuetral and ground. I plan on homerunning all of the outlets back to the breaker box and somehow dealing with connecting them to the same circuits etc. Jim

Sorry, plastic boxes don't need the 4th wire, NOR do you need IGR's. With home runs per outlet, just tie the three wires to the normal terminals at the receptacle and, at the panel, ONLY connect the bare ground wires to the common ground bus bar in the panel - Make sure ALL these runs tie their Hot wires to the same leg(phase), even if they're on different breakers - DONE... Steve

Steve, You ARE the man! You just saved me lots of headache... not to mention money! Thanks! Jim

knightfly wrote:

Here's a link to a 6 page thread on RO where we thrashed this to death some time back - rather than regurgitate all of it, you can find pretty much everything you need here, including relevant code sections to show your inspectors, electricians, etc - http://www.recording.org/posts16729-0.h ... highlight= Grab a cup of coffee and some snacks, this will take a while... Steve

That link is dead.

Quick question for a newb. When running a "home run" for each recepticle, does recepticle refer to the BOX, or the OUTLET? IE, in a 2-gang box, do I need 2 home runs or just one? I can daisy-chain the black and white, though, right? MPEDrummer

When running a "home run" for each recepticle, does recepticle refer to the BOX, or the OUTLET? IE, in a 2-gang box, do I need 2 home runs or just one? I can daisy-chain the black and white, though, right?

Outlet. You need 2 home runs. If you're installing metal boxes, you need 3 home runs. One for each outlet, and one for grounding the box, and make sure you use isolated ground recepticles.

I'm in the process of installing the electrical in my studio. I have hired an electrician who is letting me help him with the install. We are putting in a star grounding system but I have a few questions. I know this has been asked before but how crucial is it to have separate grounds to each receptacle in a 2 gang box? I'm wondering if the ground loop is as bad with a short length of wire connecting two receptacles. Is the hum you get from a ground loop always the same volume or does it vary depending on the length of ground wire? If you can have ground loops between the two receptacles in a 2 gang box then can you have ground loop problems from the two plugs on a single receptacle? I am having switches installed to turn my soffit mounted powered speakers on and off. Are they going to cause any grounding problems or do we just wire them normally? Thanks, Lief Stevens

Pertaining to star grounding, I've hit some bumps this last week... I'm in Brooklyn and I can't use Romex (because of rodents here its against code). I also have to use metal studs in any remotely commercial build. So we started yesterday with 1" EMT to allow for enough space for the home runs (12 gauge) from out IGR's and the electrician we've had on site before said we need to be using BX. When we said we had IGRs he pointed us to MC BX which has a third green ground wire present. However, the 12-3 BX can't daisy chain because we only have 3 wires total and can't add a separate ground as we go through multiple outlets on the same circuit because the IGRs only connect with the ground at one screw (which is neccessary for them to isolate the ground) where as the neutral and hot can chain with the two screws present. We can't get BX that is just ground wire and don't want to tape off BX for all the iso grounds and run it separate because at the end of the chain we'd only need one ground wire. So, to overcome this problem we are running 12-2 BX, with our outlets in series on each circuit and running 1/2" seal tight (metal flexible conduit) parallel with the BX entering the box to extract the home run iso ground wire (12 gauge) and moving with the BX to the next box to add another ground wire. As far as we have read, the seal tight is in code and we're running the BX and home runs in close proximity so we should be fine but I can't say I've ever seen this done. Any suggestions on this project? EMT is out, its a serious pain to run and we have to use 5" boxes with 1" EMT which is limited as far as available drywall adapter sizes and other neccessary parts.

How many receptacles are you running in series for each circuit? Do you have any kind of electrical layout plan or drawing you can post? Typically, you'd have the following for each receptacle in a metal box: Black=Hot White=Neutral Green1=Ground on IGR - Wired directly to Star Ground Green2=Attached to metal box (or per local code) Perhaps have a junction box where you feed the larger 1" conduit (or bigger), then branch out to your individual receptacles that will be on the same circuit using 1/2" or 3/4" conduit. The Black (hot) and White (Neutral) can be daisy chained to multiple receptacles. The main thing is keeping that ground wire isolated for each IR receptacle and taking it all the way to the Star Ground point. When I wired my room, I had no more than 4 receptacles (Two Dual receptacles). It was a pain keeping all those ground wires straight in my head. But each IGR has its own ground going back to the panel / Star Point.

I've got something working, its going like this... 8 receptacles wired in series (two gange 4" box) 12-2 BX feeding each receptacle going in and coming from the next box (or panel in the case of the first box) 12 gauge blk and wht jumpers bridging the two receptacles in the box. 1/2" seal tite flexible conduit feeding each box from the side or bottom in and out Eight 12 gauge THHN green wires were put in the seal tite before and as its run from the panel and each box As the seal tite passes through each box 2 wires feed the two receptacles (making the chain go 8 present in the first box, then 6, then 4, and then 2 feeding the last box) the seal tite is run from the panel iso ground buss bar and each wire is attached to the single iso ground screw on the IGRs The BX acts to ground the receptacle to the box but the pin is isolated to the wire straight to he buss bar. Buss bar feeds the copper bar in Earth. The max # of cables that may be placed in 1/2" conduit is 10. Eight is difficult enough to put in the seal tight with a fish. So the max number of receptacles can be 10 but we're going with 8 on a 20 amp breaker as there won't be a load present over 16 amps on the circuit.

Each IG safety ground wire has to be grouped and routed in close proximity with it's hot and neutral wire. This means in the same conduit. I think that you are overdoing the star-ground idea. Wire your 8 receptacles wired in series (two gang 4" box) to a common point in one of the boxes then run one cable to the breaker panel.

Hi all, another newbie showing up and asking questions... I actually have a few questions with regards to grounding in this case. I plan on building a new building for a small studio (I cannot give a whole lot of details, as I am in the initial brainstorming phase of it - haven't even hit the design yet). As I planned on placing this on my residence land, when I upgraded the electrical system for my house I placed a 400amp meter base in my yard, with a 200 amp leg going to my house. I plan on putting this building on, with the front half being the garage and the back half as the studio. I plan on installing two 100 amp entrances from my meter base to the building (with totally separate load centers) - one for all the lights (and any shop tools I need), and a second which only will power my audio equipment. So, my questions: 1) As I have a totally separate load center from my house, is it necessary to bond to the same ground rod as my house? Will NEC allow a totally separate ground for this load center? 2) With regard to the star grounding method, if I were to place two receps in a two gang plastic box, utilize 14/3 wire, phase tape the red wire to green, pigtail the hot wires together and common wires together, then use the red wire for one ground and the bare for the other, would this meet the spirit (and letter) of star grounding, while saving some cost in romex? 3) In my control room, should my PC and/or (video) monitors be on the "lighting" panel, or on the "audio" panel? 4) In eliminating ground issues, is using multichannel strips in the outboard gear (in the control room) a huge no-no? Should I simply have one recep available for every piece of studio gear?

That's a lot of technical questions, let me think about it and get back later. But quickly: a) A separate building will require a additional ground rod. b) You may not be able to have two main panels in the studio. c) One plug plugs into one receptacle, a dual box outlet can hold four receptacles. d) A star ground is not the be all and end all of grounding. If you need long wire runs to make the star, you are not gaining anything. e) That ground rod has nothing to do with reducing EMI/RFI it's a safety feature. f) Read the following papers: The Bill Whitlock of Jensen Transformers Seminar paper http://www.jensen-transformers.com/an/g ... eminar.pdf The Jim Brown of Audio Systems Group white paper "Power and Grounding for Audio and Audio/Video Systems" http://www.audiosystemsgroup.com/SurgeXPowerGround.pdf "The TRUTH" from ExactPower of Middle Atlantic Products http://www.exactpower.com/elite/wpapers.aspx or a different version of the same paper "Power White Paper" from Middle Atlantic.com http://www.middleatlantic.com/power.htm

Thank you. I will look into these. I guess I should have been a little more clear in my wording - I have (my entire life) called a duplex outlet a "recep". My thought was that it is a bad idea to daisy chain duplexes together for grounding, so by using 14/3 and phase taping the red to a ground, it would avoid the problems in a dual gang box.

When we talk about the problems with daisy chains, it's the many feet of wire from outlet to outlet. Bill Whitlock writes that the best thing that those fancy power conditioners/surge suppressors outlet strips is that they connect all the grounds together and all the neutrals close together. I would use 12-2 cable and not over-think the plan. If you are using NM (Romex) cable and all the receptacles in one outlet box are on the same cable, you don't need the expensive IG (Isolated Ground) receptacles. NEC rules are very complex, so I'll let your electrician and the "inspector" work out the two main panel idea. But remember that all the ground rods need to be connected together.

Me overthink something? You've been talking with my family, haven't you? While I'm overthinking things, is there a particular reason that I would want to run 20A circuits (12/2) rather than 15 amp circuits (14/2)? I really don't plan on setting up 1500 watt power amps into any part of this studio, so I thought that running a few more smaller circuits would be beneficial compared to fewer larger circuits (protection of equipment in case something "bad" happened).

While I'm overthinking things, is there a particular reason that I would want to run 20A circuits (12/2) rather than 15 amp circuits (14/2)

I'm kind of with you on the over-design thing, Bob! Having a little extra margin is always a good thing in my book, especially with electricity. Thicker cable means lower resistance, means lower losses, means cooler wiring, etc. (OK, so only slightly). And maybe you don't have any 1,500 watt speakers PLANNED right now, but who knows what you might need to do a year or three down the line, for some crazy session that you never even imagined? In any event, what about your lighting and HVAC? They will have to get power from somewhere. Will they be powered by the same cable? Lights can easily run you several hundred watts, and your HVAC could conceivably draw a thousand. If those are going to be powered from the same panel (on separate circuits, of course) then you just ate up all your spare capacity. And what about service power? (as opposed to technical power). You don't want to plug in things like vacuum cleaners, coffee pots, refrigerators, copiers, and suchlike to the same circuits as your equipment! That needs to be separate too. I'd suggest that you draw up a list and rough sketch of the layout of your electrical system, to see what things can go on the same circuit as each other, and what things need their own separate circuit, then work it back from there to figure the layout of your distribution panel(s), the rating of your breakers and wiring, grounding, etc. And even then I'd leave a healthy margin on top of each circuit, because Murphy has a habit of throwing you curve balls when you least want one... - Stuart -

Before I hijack this thread (it's supposed to be covering star grounding), we can discuss that on another one.

About star grounding... is it advisable if the supplier gives me balanced power (ie, sepparate hot, neutral and ground)? Not sure if star grounding only affects to unbalanced power... Many thanks!!