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PostPosted: Thu Sep 21, 2006 6:32 am 
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Location: Pittsburgh, PA
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


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PostPosted: Thu Sep 21, 2006 7:06 am 
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Location: Music City
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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.


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PostPosted: Fri Feb 23, 2007 1:47 am 
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Location: Asheville, NC
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


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PostPosted: Wed Sep 23, 2009 10:43 am 
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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.


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PostPosted: Thu Sep 24, 2009 6:40 am 
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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.


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PostPosted: Sat Sep 26, 2009 9:09 am 
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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.


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PostPosted: Sat Sep 26, 2009 11:22 pm 
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Location: Cleveland, Ohio, USA
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.

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PostPosted: Tue Oct 27, 2009 1:52 pm 
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Location: Southwest Michigan USA
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?

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Bob


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PostPosted: Wed Oct 28, 2009 12:28 am 
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Location: Cleveland, Ohio, USA
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

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PostPosted: Fri Oct 30, 2009 12:29 am 
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Location: Southwest Michigan USA
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.

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Bob


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PostPosted: Fri Oct 30, 2009 12:49 am 
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Location: Cleveland, Ohio, USA
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.

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PostPosted: Fri Oct 30, 2009 12:55 am 
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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).

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Bob


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PostPosted: Fri Oct 30, 2009 1:45 am 
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Location: Santiago, Chile
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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 -

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I want this studio to amaze people. "That'll do" doesn't amaze people.


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PostPosted: Fri Oct 30, 2009 2:31 am 
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Location: Southwest Michigan USA
Before I hijack this thread (it's supposed to be covering star grounding), we can discuss that on another one.

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Thanks!
Bob


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PostPosted: Tue Nov 24, 2009 1:45 pm 
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Location: Madrid, Spain
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!!


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