Couple of questions about isolated ground . .
mpmusicny
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22nd February 2012
Old 22nd February 2012
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Couple of questions about isolated ground . .

First so many thanks to the contributors here - I can't tell you how much I've learned from you guys, and especially Rod for your awesome book. . .


Hi - my composing room now has a machine cabinet next door where all the computers and drives are going to be stored. I wish to run an isolated ground circuit for this gear. Here's the questions -

1. I have read variously either that the isolated ground can be run back to the sub panel which has been installed in the studio room, or conversely that it has to be run all the way back to the house's main service panel. Can anyone explain which is true, or best?

2. In addition to the machine cabinet, there is a floor receptacle under the desk feeding - 2 speaker monitors, 2 computer monitors, a couple of usb hubs - everything else runs in from next door. Should this floor receptacle be on an isolated ground circuit also?

thanks!

Malcolm
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22nd February 2012
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Here we go again.

If you run an isolated ground from your Isolated ground receptacle back to the sub panel or main panel ground, both grounds will have the same potential and
and you would be running two wires (or one wire and sheath) which are the same back to that ground bar.

If you actually create a "separate ground" meaning, you have the existing system ground and run a ground rod which would connect to another isolated (floating) ground in the panel........ you've created a different potential to that ground from your system ground and could become a dangerous situation.

As per the NEC, your not allowed to do this except for certain commercial installs.
I think with the NEC there are certain "laws" which should be followed, but sometimes there are calculated risks someone may take on installs that violate the "laws" that to me are not a big deal. However, deriving (creating) a separate ground is against the "law" and in my opinion and others "dangerous".

So if your running a separate isolated ground back to the same system ground, I'd say go for it. If your running a separate isolated ground back to a separately derived ground, I'd say rethink it.

That's all.
mpmusicny
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22nd February 2012
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Hi ritelec,

I appreciate the need for clarification. I am aware of the perils of separate ground rods, that is not my intention. Definitely the former. 12/3 + G with the red wire tabbed for ground, run directly back to the panel. System ground bare wire connected to the metal case, isolated ground wire connected to the ground connector on the receptacle. That would be the plan.

So by saying either would have the same potential, you are telling me there's no disadvantage in running the isolated ground back to the sub?

Thanks for you help!

Malc
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22nd February 2012
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. . . and re: "here we go again"



I did a search on every post here regarding isolated ground. There was one post mentioning that sub panel or main panel made no difference - I found no mention of this specific topic anywhere else. Am i missing this specific question being done to death somewhere? Sorry if that's the case . . .

M
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22nd February 2012
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Quote:
Originally Posted by mpmusicny View Post
Hi ritelec,

I appreciate the need for clarification. I am aware of the perils of separate ground rods, that is not my intention. Definitely the former. 12/3 + G with the red wire tabbed for ground, run directly back to the panel. System ground bare wire connected to the metal case, isolated ground wire connected to the ground connector on the receptacle. That would be the plan.

So by saying either would have the same potential, you are telling me there's no disadvantage in running the isolated ground back to the sub?

Thanks for you help!

Malc

If your running to main or sub ground it's the same ground.
However, you would probably want to take it back to the Main panel ground.

12-3 ...... 1 ground to iso ground, 1 ground 2 metal ground sure why not.
remember its the same thing......but 2 seperate wires.



As a thought..........12-2 to a plastic box, regular receptacle.
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22nd February 2012
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A isolated ground circuit to me is this: A dedicated circuit that has a dedicated ground wire back to either the Main panel OR subpanel, this means IF you use metal conduit (EMT) for example you do NOT use the conduit for the ground, you have Three wires back to the Panel...It also means you MUST use those orange Isolated ground plugs...
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22nd February 2012
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If you have a sub panel, then use it. If you run all the way back to the main, then do that, but don't do half/half. I.e., don't take power off the sub, but run the ground back to the main, because then the main breaker in the sub will have a bypass.

The real reason to run an isolated ground is this: If some equipment on your circuit shorts out to the ground, then it will dump hot to ground. If you are touching the grounded cabinet of another piece of equipment on that circuit, it is potentially dangerous -- the electricity will flow through the cabinet on the way to the main (until the breaker trips). This is primarily an issue in industrial settings where you have people touching the machines all day long.

Any electric noise on the ground will be shared through the entire system, no matter what, because all the grounds and all the neutrals are tied together in the main panel.

There's no advantage to running 12/3 the way you describe, because at the other end of your run, both wires are tied together on the ground bus.
mpmusicny
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22nd February 2012
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So just running the bare ground wire in a 12/2 directly back to the panel? I read my methodology in the Black and Decker Wiring book and must admit I never questioned it -- I guess running the bare wire in a 12/3 to the system ground is simply an extra safety measure?
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22nd February 2012
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Quote:
Originally Posted by nosebleedaudio View Post
A isolated ground circuit to me is this: A dedicated circuit that has a dedicated ground wire back to either the Main panel OR subpanel, this means IF you use metal conduit (EMT) for example you do NOT use the conduit for the ground, you have Three wires back to the Panel...It also means you MUST use those orange Isolated ground plugs...
Yes if you want an isolated ground and you also have a ground through the raceway or sheath.

If there's no metal raceway or sheath, eg. the 12-3 or 12-2 nm, just use the ground......it's isolated
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Quote:
Originally Posted by mpmusicny View Post
So just running the bare ground wire in a 12/2 directly back to the panel?
yep, and use a regular receptacle.

edit: make sure your run back to the panel is not parallel with other circuit conductors. (keep like an 8' spaceing or more if so). If you have to cross separate circuit conductors do it perpendicular to those circuits. If you find you getting noise, hiss, humm, clicks, pops (which you may not). It may becomeing from an AC circuit, or washer, or dryer, or dimmer etc... and not just yours but maybe a neighbor who's fed from the same transformer. If so.... you can Isolate "your" power at "your" gear by plugging in a balanced power ac conditioner in that circuit you ran, and plug everything into it.
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22nd February 2012
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Quote:
Originally Posted by ritelec View Post
Yes if you want an isolated ground and you also have a ground through the raceway or sheath.

If there's no metal raceway or sheath, eg. the 12-3 nm just use the ground......it's isolated
That's why I mentioned Conduit, in a residential area it's romex, and yes the ground IS isolated..

By the way, I did electrical work for several years before I went into electronics..
mpmusicny
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22nd February 2012
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Quote:
Originally Posted by piper View Post

The real reason to run an isolated ground is this: If some equipment on your circuit shorts out to the ground, then it will dump hot to ground. If you are touching the grounded cabinet of another piece of equipment on that circuit, it is potentially dangerous -- the electricity will flow through the cabinet on the way to the main (until the breaker trips). This is primarily an issue in industrial settings where you have people touching the machines all day long.

Any electric noise on the ground will be shared through the entire system, no matter what, because all the grounds and all the neutrals are tied together in the main panel.

There's no advantage to running 12/3 the way you describe, because at the other end of your run, both wires are tied together on the ground bus.
Piper - you sure? From the Black and Decker site -

Quote:
An isolated-ground circuit provides protection beyond standard surge suppression for computer equipment, and it also significantly reduces the potential for electromagnetic noise from the common grounding path. This noise may interfere with the proper function of sensitive audio and video equipment by causing an audible hum or poor picture quality.
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22nd February 2012
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Quote:
Originally Posted by nosebleedaudio View Post
By the way, I did electrical work for several years
Sux,don't it !!!


mpmusicny
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22nd February 2012
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ok then, so let's say I have metal boxes, romex #12 throughout, no conduit anywhere is there a consensus on how best to wire an isolated ground back to the sub? Also, if i may selfishly steer back to Q #2, should the desk gear be a separate isolated ground circuit?

Much appreciated, guys!

Malc
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22nd February 2012
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ritelec,

Just to be clear in the context of other comments here, when you say "regular receptacle" do you mean plastic, or non-orange color coded? (Not going plastic, btw . )

M

Quote:
Originally Posted by ritelec View Post
yep, and use a regular receptacle.

edit: make sure your run back to the panel is not parallel with other circuit conductors. (keep like an 8' spaceing or more if so). If you have to cross separate circuit conductors do it perpendicular to those circuits. If you find you getting noise, hiss, humm, clicks, pops (which you may not). It may becomeing from an AC circuit, or washer, or dryer, or dimmer etc... and not just yours but maybe a neighbor who's fed from the same transformer. If so.... you can Isolate "your" power at "your" gear by plugging in a balanced power ac conditioner in that circuit you ran, and plug everything into it.
#16
22nd February 2012
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Quote:
Originally Posted by mpmusicny View Post
ritelec,

Just to be clear in the context of other comments here, when you say "regular receptacle" do you mean plastic, or non-orange color coded? (Not going plastic, btw . )

M

If you use a plastic box.Use 12-2 nm with ground and the ground goes to a "regular" type receptacle ground.

If you use a metal box.......you can do the same thing but you have to ground the box....
OR...run the 12-3 nm with ground and the ground goes to the box, and an insulated conductor of the 12-3 goes to the ground termination of a isolated (orange) ground receptacle. The bare ground and iso ground get tide in at the same point at the panel.
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22nd February 2012
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Quote:
Originally Posted by mpmusicny View Post
ok then, so let's say I have metal boxes, romex #12 throughout, no conduit anywhere is there a consensus on how best to wire an isolated ground back to the sub? Also, if i may selfishly steer back to Q #2, should the desk gear be a separate isolated ground circuit?

Much appreciated, guys!

Malc
I have a 12-2 (20amp) separate circuit from my main panel to my room that feeds a single 20amp receptacle for the gear (regular circuit..ground is ground).

Lighting and other convenience outlets are not on that circuit.

Into that regular single 20amp receptacle I plug a balanced power Furman.

From the receptacles on the furman...... I made several 12-2 nm extensions.
A male cap on one side, a plastic box with regular receptacle on the ther side.

These 12-2 extension go about the room that ALL my gear plugs into. eg. computer, drives, amps.....everything........

Complete silence when anyone turns on a dimmer in the house or does the wash etc......
mpmusicny
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22nd February 2012
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Cool, thanks ritelec

Malc
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22nd February 2012
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Quote:
From the receptacles on the furman...... I made several 12-2 nm extensions.
A male cap on one side, a plastic box with regular receptacle on the ther side.

These 12-2 extension go about the room that ALL my gear plugs into. eg. computer, drives, amps.....everything........

Complete silence when anyone turns on a dimmer in the house or does the wash etc......
Ingenious .. . but i gotta ask this,

is it code?
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22nd February 2012
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Quote:
Originally Posted by mpmusicny View Post
Ingenious .. . but i gotta ask this,

is it code?
If I made a heavy duty extention cable I prefer 12/3 SO cable..It IS to code and better..
#21
22nd February 2012
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Is it code? The Furman......

YES..........that's why I did it this way.

I pulled a separate ground electrode conductor to my water meter, started researching iso transformers, getting ready to install a separate isolated panel.....long story short.

Plugging in something like the Furman (there are other units out there) which is a piece of equipment is the only "legal" way to do it.

Do realize though......the furman and other units do separate (isolate) the ground at the unit. There is the possibility of a shock or electrocution if there is a problem somewhere between the furman ground and your house ground.

Just keep the two systems separate (for instance , odds are nothing would happen but keep it in mind if your touching the guitar and turning the room light on or off.....or you have a clock or something plugged into a convenience outlet and you may get caught between the two...... Nothing will happen, but keep it in mind).

To note. when I first installed the system, I was getting a humm.....$1700 on the Furman, man I was bummed. Then thought about it. I installed my gear in a rack including the Furman. All the chassis where connected via the screws going into the rack. The Furman chassis is part of the "incoming" ground (the chord your plug the furman in...house ground) I removed the furman from the rack rails which separated the Two grounds..Silence!
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22nd February 2012
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Quote:
Originally Posted by mpmusicny View Post
Ingenious .. . but i gotta ask this,

is it code?
Quote:
Originally Posted by nosebleedaudio View Post
If I made a heavy duty extention cable I prefer 12/3 SO cable..It IS to code and better..
The only code violations I would see with using the nm as an extension chord is wiring methods "protecting it against physical damage" "means of support".

Those where the "calculated risks" as mentioned in my first post.

Would someone really damage the nm? Does it need support?

If there's a problem using the nm as an extension chord, by all means go for a rubber cord. (14 gauge or 12.......what ever floats your boat......maybe even 16 gauge).

Edit: by the way, the exception for supports of the nm where supporting is not required is where it's snaked (fished), most of my nm extension cords are snaked behind and through the walls. Also where exposed, there not exposed to physical damage..........

Something how we can twist and convolute things in our own minds isn't it????

Good luck with it....


Rich
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22nd February 2012
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Quote:
Originally Posted by mpmusicny View Post
Piper - you sure? From the Black and Decker site -

Quote:
:
An isolated-ground circuit provides protection beyond standard surge suppression for computer equipment, and it also significantly reduces the potential for electromagnetic noise from the common grounding path. This noise may interfere with the proper function of sensitive audio and video equipment by causing an audible hum or poor picture quality.
B&D isn't really an authority in this field, I don't think. Then again, neither am I

I think they're mixing up two issues. If you have, say, a blender and a stereo on the same circuit, you'll get more noise than if the blender is on a different circuit, because the noise has to go down the wire, through the bus, and come back out. So using separate circuits is a good thing.

But you're talking about running two wires back to the box instead of one. There's no advantage to that.

When they say "common grounding path" what do they mean? In residential applications there is only one ground, and it's the same thing as the neutral. So they're really just talking about the path. If your audio is on a different circuit, then it has a different path. That's assuming modern wiring. In some old wiring you might find a shared ground. But you're running a new circuit anyway.

I have an Antec power supply here, and the ground from the outlet is tied to the case. That's it. It won't matter one bit for this particular power supply if it's even grounded, so long as there's not a short in it from a hot to the case. A lot of modern audio stuff isn't grounded -- two prong power supplies.

I can't help but think that a lot of the "isolated ground" talk comes from people who don't understand that not only are all the grounds tied together, but all the neutrals are tied to all the grounds too.
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22nd February 2012
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I think B+D's point is that they are suggesting not to have the ground dependent on metal/physical means. eg. metal to metal clamps straps and screws....

But to establish a good ground path......via a conductor.
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22nd February 2012
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Quote:
Originally Posted by piper View Post
I can't help but think that a lot of the "isolated ground" talk comes from people who don't understand that not only are all the grounds tied together, but all the neutrals are tied to all the grounds too.

Only at the first overcurrent protection device. Main Breaker.

Yes, the neutral and ground are bonded.
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Quote:
Originally Posted by ritelec View Post
I think B+D's point is that they are suggesting not to have the ground dependent on metal/physical means. eg. metal to metal clamps straps and screws....

But to establish a good ground path......via a conductor.
I think that's code now, anyway (i.e. don't rely on conduit, which might corrode.)
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Quote:
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I think that's code now, anyway (i.e. don't rely on conduit, which might corrode.)
Nope, not yet. Metal raceway can still be used for earth.

Lets say you use type ac (armor clad). The metal sheath is rated for ground.

MC (metal clad) there's a separate insulated ground conductor and the sheath is not rated for ground.

There's also another type of MC where there's a separate ground conductor and the sheath is rated for ground (that could get you the isolated ground if you needed one).



Oh.....mpmusicny.......by the way... If you go with the 3 wire nm and use the red as ground it would not be "code" compliant......
(but I won't tell).
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22nd February 2012
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Originally Posted by ritelec View Post


Oh.....mpmusicny.......by the way... If you go with the 3 wire nm and use the red as ground it would not be "code" compliant......
(but I won't tell).
Why would that be ritelec?
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22nd February 2012
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It would have to be green, green with a yellow stripe, or bare for the entire length. Only when you get into larger size wires are you allowed to tape it for color coding.

They do make wire assemblies if you want to run a ground with isolated ground......but using the red and stripping or taping the red green would be a violation.

(again..I won't tell)
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22nd February 2012
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Most interesting - just did a quick Google of "isolated ground red "green tape"" and everyone apart from Black and Decker's book is in agreement with you, though there are a lot of "technically"'s and "strictly speaking" thrown in - kinda like your "I won't tell".
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