Setting forms Monday!

[Michael Jones]

My concrete contractor is comming out Monday morning to set forms for the foundation!
Anybody know what anchor bolt spacing is supposed to be?

 

[RICK FITZPATRICK]

Hi Michael, are you doing any kind of custom forms for cable chases?
fitz

 

[Michael Jones]

Yes, I am.
I'm having them do a series of 6"x4" troughs for audio cables.
I'm also setting copper rods attached to copper mesh for star grounding.

 

[DigitalDon]

Michael,
Great to hear you've got it going. Mine's almost done. Well, kinda. Still a lot of little stuff to do. It's actually a break going to work today (Saturday). Overtime - Yeah. I keep telling myself I'm not getting older but my body (especially hands, knees, feet) has reminded me a lot lately that I'm not used to manual labor.

You were talking about putting in copper rods, etc for star grounding. Better check with the local electrical code guys. I might be mistaken but I think the NEC prohibits any earth ground other than the one at your main service entrance panel. I think it has to do with safety issues if you lost the neutral line in your building but I'm not sure.

Anyhow, glad to see you're rolling now. I'll try to post some more pics this weekend.

DD

 

[RICK FITZPATRICK]

Hi Michael, say, I think DD is right, that is unless your getting power to the studio right from the pole with its own supply seperate from the house. But if your installing a sub panel from the house supply panel, don't use a seperate ground rod as it creates a second ground potential. At least thats what I was told. It wrecks havoc on audio! Here in my county, your outbuilding has to be 160' from the house supply, before they will run another line to the property. Couple of questions. How are the cable chases terminated at the wall? In other words, are your mic lines coming from a box in the wall in the studio or how are you treating this detail? Also Michael, did you ever get the sliding door details worked out. I'm still in the dark about how other people detail their regular and sliding door/jamb stops for isolation. Can you elaborate, as I have NEVER seen any details on the forum regarding this. Appreciate it. And congrats on the start Monday. I bet your getting very excited. Hows the weather holding? I thought you were in the middle of reallly cold weather Makes for no fun working outdoors. Good luck with the slab.
fitz

 

[Michael Jones]

OK, maybe I'm not understanding something here.
Here;s what I have, and what I'm getting:

I currently have a single phase - 200 amp service and meter to my house.
The electric company has agreed to provide an addittional single phase - 200 amp service and meter for the studio, but since the proximity of the 2 structures is less than 160', the new meter has to be mounted next to the existing meter.

From that point, the new service will go underground to a new main distribution pannel located outside and adjacent to the studio.
That main pannel will tie into an interior sub pannel or breaker box.
So given that, you're saying I should have only one ground on the new service, outside, next to it?
I'll ask the electrician, but I thought you could have as many grounds as you wanted, providing that each ground is for a dedicated circuit.

Something else to double check.

The mic lines will go from the console, down to a trough set in the concrete. The trough terminates at the control room wall just inside the control room. The cables will then come up, and out of the trough, into a conduit, and tie into a pannel with xlr and 1/4" connectors on it.

The pannel will penetrate the wall on the tracking room side.

For that small portion of exposed conduit, where they come out of the trough, I'll have a trim piece, made of wood, that will look kind of like a square tube. It will cover the conduit and then this will be mounted onto the plate that will cover the trough.
This happens at the tracking room, the drum room and the vocal booth.
Remember, I have dual walls between the tracking room and the control room.

(Special thanks to "Snapper" for the photos)

 

[DigitalDon]

Michael,
It's my understanding the earth ground (copper rod) has to be tied into the breaker panel where your service enters the building. Also, this breaker panel will come with a green screw which is used inside the breaker panel to tie the incoming neutral line to equipment ground. Most local codes require this screw. to be used. I loaned my NEC book out last week or I would look it up for you.

I think the distribution panel you are talking about is just the box used to make the transition from underground to your building service entrance. There might be a main disconnect switch here but I'm not sure. Also, a subpanel would be any panel placed after the main breaker panel in your building. Seperate earth grounds are not permitted past the main breaker panel. If you like I'll get the name of the book I bought. It's the best I've seen and in laymen terms (thank goodness). It's got a lot of good info about conduit too like maximum number of wires and inductance that can build up inside the conduit.

Did the power company tell you they will charge a higher rate (per kilowatt hour) on the second meter? That's what they do here. Your home service is actually considered a "discount" rate which is recouped by charging higher "commercial" rates for a second meter. At least that's how they do it here.

Hope this didn't confuse things. Oh yeah, I just went through my 3rd box of 1,000 screws for RC and sheetrock. Damn I'm tired of screwing around

DD

 

[Michael Jones]

Thanks Don.
You're right.
I checked the Uniform Electric Code, and the Local amendments to it. It's what we use in Austin, and is very similar to the NEC.
It allows for only one ground, at the main pannel.
So given that, how do you eliminate the possibility of a ground loop hum?
I know you ground all the outlet boxes, but if one ground is faulty, or comes loose, you'll get a ground loop hum.

My father sold medical equipment for General Electric, and designed the room layouts and electrical systems for big, massive X-Ray , CT Scanners, and MRI units. These systems required super high voltage, on the order of 10's of thousands of volts, with super low current, on the order of mili-amperes to operate. They frequently used star earth grounding to eliminate noise that could interfere with a sine wave and it's associated KV peak.

I guess the code is considerably different for medical systems. But there's gotta be a way to insure the elimination of a ground loop?

 

[RICK FITZPATRICK]

Hello Michael, electrical ground system design has been the root of hundreds of threads in audio forums. The best explaination I have seen(I'm a total amatuer) is by a guy named Larry Robinson on the Tascam analog forum. Needless to say, a single earth ground is absolutely essential. Your second service panel should be grounded by a single rod, and not tied to the house ground or more than one earth grounding point I don't profess to understand completely, and don't care to as its another profession and don't have time for even studio design studys But the star ground system is something he explains thoroughly, even to the extent of audio line "ground loop isolators" which are transformers inserted into -10 audio lines where needed, and can be purhased even at radio shack. They sell cables with the transformer built into one end within the plug I believe. There are other types also with multi tranformers for up to 8 lines. I can't explain the theory behind them, although I understood it when I read it. I suggest you read it. Great stuff. Had to tear out all my wiring and start over as I too had a second earth ground rod at my studio sub panel Learn somthin new everyday, but damn I'm tired of tearin out stupid ideas. Thats why I ask so many friggin questions now. And since I read what John said about he's seen "hundreds of feet of RPG torn out from incorrect design" thats why I questioned you about your diffusers. I'll be damn if I'll build stuff that I have assumed something only to have useless items that took good time and money to build but do not really work. Anyway, hope this helps a little bit. Check out Larry Robinson. He's REALLY togeather, and has the electronics/recording thing down pat.
And thankyou Michael for sharing your studio building experience with us and responding to my questions. I will be asking many as I plan on doing the same as you next year

PS- don't confuse your earth ground point with circuit grounds, which all return to the ground buss(or neutral buss sometimes in older equipment) I had a supply panel grounded to a water pipe, but ran a subpanel to the studio/shop, and grounded it to its own rod, as well as tied the ground wire from the supply panel to it also. Thats a no no. I did find out that the "hot" conductor is refered to as the "non grounded conductor, and the "neutral" is refered to as the "grounded conductor" and the ground is ground. This eliminates confusion. In a standard home supply(breaker box) you have 2 non grounded conductors(120v potential) when measured to ground(or neutral) but they are 180 degress out of phase with each other and (240v) when measured between the 2 non grounded conductors. The neutral is grounded at the supply box to insure ground potential at the home end of the line, with a ground wire usually going out to a water pipe or ground rod. I'm definitely not a pro, so if someone sees something here that is incorrect, feel free to flame me. I deserve it when it comes to this stuff. Just trying to help with what I understand.

 

[TexRoadkill]

I was always under the impression that a Star Ground was when each outlet had a dedicated ground cable to the main grounding rod as opposed to daisy chaining the ground cables from outlet to outlet as is the usual practice.

I am planning on taking the easy route and just run a new conduit into my control room with a well grounded junction box and connect some power condtioners off of that line for distrobution.

 

[RICK FITZPATRICK]

I was always under the impression that a Star Ground was when each outlet had a dedicated ground cable to the main grounding rod

Hi Tex, I beleive you are correct. What did I say that made it sound any different?
fitz

 

[John Sayers]

I was always under the impression that a Star Ground was when each outlet had a dedicated ground cable to the main grounding rod

yup - that's why I'm confused about where the problem is?? all your earths from your outlets will have to reach the star point from where you connect directly to earth be it in the main building or an external one - doesn't really matter??

chers
john

 

[JMarcomb]

i remember humping forms for a summer job. keeps you in good shape i guess.
I wouldnt guess the anchor spacing is too big of an issue, though Ive never put them in, but if there just for bottom plates... hmmmm..never posted in this forum before and just thought Id jump in here and act like I knew what I was talking about

 

[knightfly]

Anchor bolts need to be spaced to code for your particular location - your area may have more stringent requirements due to earthquake specifications, or less. I'd make sure with a call to building codes if it's not already spelled out on your plans.

The point of star grounding is that all your outlets get their ground reference from the same central point - that way, there's no chance of a slightly different ground potential between AC sources causing a ground current, which in turn is the cause of hum problems.

If your rack mount gear is grounded to chassis, and that chassis is in turn grounded to the rack, there is a potential for ground loops caused by signal cable shields also trying to be the ground reference.

In permanent installs, you can build custom cables where necessary that use telescoping shields (only one end connected to ground) so that there is no chance of ground current flowing in the (static) shield. This needs to be done on a case by case basis to eliminate hum. (The transformers mentioned earlier can work for ground isolation also, but will do more to degrade your sound unless you spend big bux on high end transformers.)

One common way of doing telescoping shields in a studio is to use the mixer as the common shield tie point, leaving the other end of each cable's shield free floating. Another way is to use the scheme of grounding the SOURCE end of each cable shield.

Yet another way of greatly minimising noise is the balanced power method. Furman and Equitech both make transformers that change the 120 volts with ground, to two 60 VAC out-of-phase lines with ground at center, just like normal household power does with 240 VAC for stoves/water heaters/clothes dryers. There is a TON of info on this at equitech.com - they were instrumental in getting balanced power included in the last couple of NEC versions.

Equitech claims that you can get way over 12 dB improvement in noise floor just by inserting their transformer between the wall and your gear - works the same as balanced audio for canceling noise... Steve

 

[Michael Jones]

Now I'm completely confused.
So you ground each outlet at the outlet junction box, and then run an additional ground wire or cable from there to a grounding rod outside?

 

[DDev]

I think the confusion on the star grounding goes back to the assumption that Michael intended to have multiple gronding rods going to an outside grounding point, which is absolutely a bad idea (hence the NEC).

What Tex was referring to is the proper method of installing a star grounded wiring scheme that stars from the main electrical box. If you can visualize this, what you end up with is 1 ground wire that runs from the electrical box to real earth ground (your grounding rod), and numerous grounds that go from the electrical box to the individual circuits inside the building ( and this is where the "star" term comes from). Now, for the best chance at noise immunity, each outlet (not a circuit of outlets) will be fed directly from the electrical box and be individually grounded there. This is not always feasible, and is not the way a typical building is wired (it adds a lot more wire and could require a huge box to handle all the individual circuits). The thing to avoid is getting power at an outlet with a ground from somewhere else (hence the term "ground loop"). Like I said, its not always practical or feasible to go this route but if you can you take one big possibility out of the equation when noise issues arise later on. Always keep your lighting circuits separate from your power outlets, also.

Hope this helps. I have to deal with ground loop issues on a daily basis on aircraft, so this is kind a soapbox of mine.

Darryl.....

 

[knightfly]

Michael, I'll try again on the ground thing, sorry I wasn't quite clear on it -

The goal is to have only ONE connection between the ground pin on your power connector that is plugged into each outlet, back to a COMMON ground point that is earth ground. If you have more than one possible path to that ground, there is the possibility of a loop.

If your wiring is typical household wiring, the ground is made by using the bare wire included in 2-wire Romex with ground. Black = hot, white = neutral, bare = ground. Since there is no other metal connection between the outlet box and the distribution center, there is no loop. Good.

If, however, you use metal conduit and metal outlet boxes, you now have another ground path that runs from the distribution box out to each outlet box, and if you then try to use Romex and connect its ground wire, you will have TWO ground paths between the distribution box and each outlet box. NOT good. Generally, if a system is done in metal conduit, separate conductors are used for hot and neutral, and the outlet ground connector is wired to a screw inside the outlet box.

If you look at a typical U-ground 120 volt outlet, you'll notice that the green screw goes into a metal tab that is part of the frame of the receptacle, so that when you screw the receptacle into the outlet box (assuming the box is metal) you now have a connection from the ground node in the receptacle to the metal outlet box. If that metal outlet box is bonded to metal conduit that runs back to the distribution box (breaker panel) then THAT is your ground, and you need NO WIRE connected to the receptacle. However, NEC still REQUIRES it, so in that case a short wire is connected from a screw inside the outlet box, to the green screw on the outlet. Even tho this technically creates a "mini" ground loop (about 3-4") it's too small to actually cause any measurable difference of potential, and can be ignored.

As long as you're using Romex for power distribution and NO CONDUIT, then the only wire needed for ground is the one built into the romex, which should be tied to the green screw terminal. The other end of this conductor ties to the ground bar inside the breaker box, which is your "star" point.

I'm not sure if these are still on the market, but there used to be outlets that you just bared the wires and pushed them into holes on the rear of the outlet - quick, neat, and STUPID!!!! Those connections will heat up when you draw any serious amount of current, and they are electrically NOISY as well - they're simply NOT good enough for reliable contact, period. Sooo, even if they are still available, do NOT use them or allow them to be used on your studio, or anything else for that matter. Stick to the ones with real screw terminals, and tighten them quite snugly. Also, don't be tempted to save a few bucks with aluminum wire - even with the paste that's available for compatibility with copper connections, it's an iffy deal. Stick with copper.

Bottom line - one way or another, you only want ONE path to a COMMON ground for each 120 volt supply point in the studio, period. Your earth ground comes to the multi-point bus bar in the breaker box, which is where each outlet should be grounded.

Also, if at all possible, have ALL outlets into which studio gear is connected, on the same PHASE of the electrical power, and everything else (plugs in bathroom, kitchen (especially refrigerators), lights, etc) on the OTHER phase. That way, not only do you lessen the chance for hum, in the event that a ground goes bad you will only get a 120 volt shock or burn, instead of a 240 volt one. Still deadly, but not quite as much so... Steve

 

[TexRoadkill]

Also, if at all possible, have ALL outlets into which studio gear is connected, on the same PHASE of the electrical power, and everything else (plugs in bathroom, kitchen (especially refrigerators), lights, etc) on the OTHER phase. That way, not only do you lessen the chance for hum, in the event that a ground goes bad you will only get a 120 volt shock or burn, instead of a 240 volt one. Still deadly, but not quite as much so... Steve

When you say phase are you really meaning 'leg'? Most homes have single phase 240 but it does come with 2 legs (2 hots). Or are you just referring to commercial double phase 240?

I may be confused because when it comes to electical work I know just enough to be dangerous.

 

[Michael Jones]

There's no such thing as double phase.
There's single phase, and three phase.

Here, unless you're a hospital or factory, or retail center, you get single phase.

 

[TexRoadkill]

Yep, Triple is what I meant.