Dedicated AC Wiring question-Isolated Ground

mmadden28

OK, I've been reading the latest threads on AC power, etc, I've been planning on replacing my outlets and putting a dedicate outlet in anyway, but now some of that has changed. I want to do it right.

I will be running a dedicated 20A circuit for my HT setup and probably for my 2 Channel rig as well. I'll use 12awg.

Here is what I need to figure out. Should I use an Isolated Ground outlet and setup? I've read it should be used on computer and Audio circuits adn that it may help eliminate or reduce any AC hum. What I read about the hookup is that I would use a 12/3 cable (4 conductors). The ground would connect to the outlet box, and the red would be my isolated ground connected to the isolated ground recepticle. Both ground and red will connect to the nuetral bus in the AC Panel. OK, makes sense except that my new outlet box is not metal-its plastic-so where would I connect the ground? Or because of that fact and because its a dedicated outlet and nothing else will be sharing the ground (in circuit)anyway, do I even need to run 12/3, and just running a standard circuit wiring but with 12/2 with an isolated ground outlet accomplish the same goal?

disneyjoe7

Isolated ground is just that isolated, but I always thought it was a transformer which could provide it? Do you have a link of what you're looking at?


The transformer would be 1:1 ratio so the primary is connected to source and the outlet is connected to the secondary lifting ground from source.

mmadden28

Actually I read it in the newest Black and Decker Home Electricity book at Home Depot. The circuit didn't really seem to do much, it essentially explained an isolated ground as simply being an isolated or dedicated ground to the panel, as opposed to sharing the ground with other recpeticles that might be on the same circuit. Nothing mentioned about tranformers or pounding my own grounding rod in or anythgin. My thinking is that if its a dedicated circuit, then its already isolated. Also not sure if the isolated ground recepticle is special in design or not or is it simply special because of its markings?

apphd

mmadden28 wrote: »

Actually I read it in the newest Black and Decker Home Electricity book at Home Depot. The circuit didn't really seem to do much, it essentially explained an isolated ground as simply being an isolated or dedicated ground to the panel, as opposed to sharing the ground with other recpeticles that might be on the same circuit. Nothing mentioned about tranformers or pounding my own grounding rod in or anythgin. My thinking is that if its a dedicated circuit, then its already isolated. Also not sure if the isolated ground recepticle is special in design or not or is it simply special because of its markings?

mmadden, I'm no electrician but have had a little exposure to isolated grounds when installing some processor systems some 20 years ago. As I believed to understand it then an isolated ground receptacle differed in design than a conventional outlet in that the ground receptacle in the plug was isolated from the rest of the outlet and the outlet box. A conventional outlet will ground any metal of the outlet and the box to the ground receptacle of the outlet.

I would think if you are not using a metal box, and you are running a dedicated circuit, then a standard outlet would give you an isolated ground. Thus needing only 3 conductors hot, neutral and ground. The equipment we installed was very sensitive to noise and power fluctuations and we even required that the isolated ground NOT be connected to the buss in the panel box and was run to a separate ground rod or cold water pipe as close to it's entry point as poss. I don't think this would be beneficial in audio applications as I think this could induce ground loops. But I don't know any of this it is just based on some very limited knowledge.

mmadden28

apphd wrote: »

...
I would think if you are not using a metal box, and you are running a dedicated circuit, then a standard outlet would give you an isolated ground. Thus needing only 3 conductors hot, neutral and ground. ....

Thanks for the info.

Jeff Beaird

mmadden28 wrote: »

OK, I've been reading the latest threads on AC power, etc, I've been planning on replacing my outlets and putting a dedicate outlet in anyway, but now some of that has changed. I want to do it right.

I will be running a dedicated 20A circuit for my HT setup and probably for my 2 Channel rig as well. I'll use 12awg.

Here is what I need to figure out. Should I use an Isolated Ground outlet and setup? I've read it should be used on computer and Audio circuits adn that it may help eliminate or reduce any AC hum. What I read about the hookup is that I would use a 12/3 cable (4 conductors). The ground would connect to the outlet box, and the red would be my isolated ground connected to the isolated ground recepticle. Both ground and red will connect to the nuetral bus in the AC Panel. OK, makes sense except that my new outlet box is not metal-its plastic-so where would I connect the ground? Or because of that fact and because its a dedicated outlet and nothing else will be sharing the ground (in circuit)anyway, do I even need to run 12/3, and just running a standard circuit wiring but with 12/2 with an isolated ground outlet accomplish the same goal?

Why would you run 4-wire and hook two of them together at the outlet box and breaker panel..?

The only way to do a true dedicated line is to totally separate ALL lines with a separate power panel and ground, split off of the incoming power. Just separating the lines should be good enough for most of us..!
But if you want to totally go over the top, Audiophile Style. You need a separate power line disconnect, outside your house w/4/0 Kimber Cable silver braided cable, teflon coated @$400 per/ft. w/solid gold (24ct. gold grounding rod 7 ft. long)... :eek::eek::eek: $$$ Kaa- ching..$$$
Yes, I have been drinking...
Not necessary at all..!
My $0.02:D

mmadden28

I spoke to a commercial electrician about isolated ground (way before I posted this thread and was even interested in running a ded. ckt) and he said something similar (IIRC) to the effect of just dedicating an isolated ground outlet and not sharing the ground with any box or other outlets except at the panel is not truly isolating. I never asked him what constitutes true isolation-I just didn't have enough interest in doing it at the time. So having a separate panel and grounding rod for a true isolated ground sounds logical.

The four wire thing, again was what was stated in the B&D wiring book. It makes sense what they said in the book, but I think that was simply isolating an outlet within a metal gangbox with other outlets-they didn't clarify much else. It didn't make sense when using a plastic gangbox, especially one that would be dedicated (lonely).

I think I'll just run my 12/2(3 cond) cable (or perhaps 10/2 :eek: depends on the cost difference), with a 20 amp breaker and 20A outlet. If I decide to run a sub panel, that will be later, and likely when I build a dedicated HT/Media room. :rolleyes:

Thanks all

disneyjoe7

mmadden28 wrote: »

I spoke to a commercial electrician about isolated ground (way before I posted this thread and was even interested in running a ded. ckt) and he said something similar (IIRC) to the effect of just dedicating an isolated ground outlet and not sharing the ground with any box or other outlets except at the panel is not truly isolating. I never asked him what constitutes true isolation-I just didn't have enough interest in doing it at the time. So having a separate panel and grounding rod for a true isolated ground sounds logical.


Thanks all

That's why I stated transformer above. The only way to have an isolated ground is thru a transformer. A bit over kill if you ask me.

ben62670

For one circuit just run 12/2. Having 2 grounds does nothing. I would personally run the 12/3, and have 2 20 amp circuits. You are doing the run anyway, and adding a breaker, and another outlet will only bump the price a small amount. I was an electrician for years;)

mmadden28

ben62670 wrote: »

For one circuit just run 12/2. Having 2 grounds does nothing. I would personally run the 12/3, and have 2 20 amp circuits. You are doing the run anyway, and adding a breaker, and another outlet will only bump the price a small amount. I was an electrician for years;)

I forget the exact discussion, but there was concern over sharing the neutral and any interference that might transfer?? I like the idea of two runs.

So, as far as current rating, would I be able to split the duplex out (remove the jumpers) and run as a dual simplex? Thereby splitting the duplex into essentially two simplex outlets, especially since the Power Ports cost $50 a pop. Cost savings right there to make up for any increase in the cable and breaker cost and less to pull and staple. hmmm :rolleyes:

mmadden28

disneyjoe7 wrote: »

That's why I stated transformer above. The only way to have an isolated ground is thru a transformer. A bit over kill if you ask me.

I didn't think you could 'ground' through a transformer, I get the isolation bit using a transformer for neutral and hot.

ben62670

Neutral is a wire running straight to ground. Ground is just a safety. Neutral sharing isn't a concern. The energy is used up mostly by the device. High current 240v devices share a neutral (like welders). I wouldn't suggest splitting a duplex into 2 20 amp plugs. It is easy to use a 2 gang box, and have 2 20amp outlets in it. You can not use a transformer to isolate ground. Ground has to be direct to ground. When I get a little time I am going to work on a ground filter I have had in my mind that I'll tell you bout later;)

disneyjoe7

If you had a transformer which was large enough to light a 100w lamp, powerd by 110vac but provided 110vac so it's 1:1, same voltage in as out. You could now ground the hot or the neutral to ground as the voltage is now floating.

I work in an issolated outlet build where theres many outlets which are orange and marked issolated ground. There used for switch printers, back to an very expensive electronic switch.

ben62670

When ever we installed an isolated ground we did use orange outlets, but it meant that the grounds were run directly to the panel with no other outlets/lights/.... on the same circuit. With the transformer as you described it would function as a ground, but would not meet code requirements as a true ground, or be safe.

disneyjoe7

Ben you have PM

mmadden28

ben62670 wrote: »

...I wouldn't suggest splitting a duplex into 2 20 amp plugs. It is easy to use a 2 gang box, and have 2 20amp outlets in it....

Yeah but...but...thats another $50.. .

Why is that anyway (not splitting the duplex)?

The neutral sharing concern was an audio quality concern not a safety one-I'll try to find that post.

Here was my thinking (for my HT rig):
One would be for my Amp and Amp alone which currently pulls maybe 9 amps steady max.
The other would be for the rest (TV, Pre-Pro, etc.).

I suppose I could still use the existing 15 amp outlet for non AV stuff like ventilation fans and such. And maybe the cable box??

ben62670

$50 is a small investment to make for now. It would cost a lot more to do in the future. Cable TV boxes are fairly known for making noise. I would try it both ways. Separate grounds are what usually cause ground loop problems;) You could split the duplex. It is rated for a single 20 amp device to run off of one outlet. Two outlets was just a preference. I would still check code on that one.

Systems

mmadden28 wrote: »

I didn't think you could 'ground' through a transformer, I get the isolation bit using a transformer for neutral and hot.

On an isolation transformer the ground would be attached to the electrostatic shield that is placed between the primary and secondary windings.This improves the isolation between them.

Or in the case of a balanced isolation tranformer( like those sold by Equi-Tech)ground would be connected to the center tap on the secondary windings.This then divides the 120 volts into 2 equal (but opposite phase)60volt sections.

mmadden28

ben62670 wrote: »

$50 is a small investment to make for now.

I know, but since I already spent $50 for the initial outlet (PS Audio Power port), and then some $ for the 12/2 cable and a breaker, and I've also been buying some upgraded power cords-... another $50 might just be pushing this beyond what I wanted to spend on this family room HT. I haven't even heard what difference a better outlet can make yet. So the small investment (relatively speaking) in just the power side of things is rapidly accumulating. :eek:
Eventually I'll be setting up a ded. HT in the basement with a ded. panel. :cool::rolleyes:

ben62670 wrote: »

It would cost a lot more to do in the future.

What would cost more?? Changing from a single gang to a double? FYI, I'm doing all the grunt work myself.

ben62670

OK OK OK I am sure the PS PP is over built. There may be a code issue. Not sure.

mmadden28

Just FYI, I just read through the latest edition of Wiring Simplified - 42 edition, which covers the new 2008 NEC, it states (Chapt 10) that when wiring a single duplex receptacle (yoke) as a 'split-wire receptacle' using two separate circuits, that there is a very specific condition placed on this setup by the NEC. There has to be a means to disconnect all ungrounded conductors (going to the receptical) at the Service panel. Its suggested to use either a multi-pole switch near the panel or simply use a multipole circuit breaker. The concern is that an untrained person might assume that the outlet is off when in fact only half of it is off.
Make sense to me, so barring any other local codes on this issue-it seems that using a 220 breaker would satisfy this requirement.
Also each circuit should be on different legs on the panel, they should not be on the same leg, and I believ the 220 breaker accomplishes that goal. Of course that that rules out my using one of those mini dbl breakers since that would put both circuits on the same leg.

Additionally--regardless of whether one chooses to split a receptacle or run to two separate receptacles, there is an advantage to running a multi-wire circuit (running 2 120 lines in a 3 wire and ground cable) over 2 separate 2 conductor and ground cables--One is savings in material cost (although I personally think the cost was negligble between the two at HD), less install labor (I'm running the cable), and also running this way reduces the overall voltage drop (compared to two separate cables), thus resulting in more available power at the receptacle--bonus! This is important to me since my HT requires a 90' run .

The chart in the book (based on the NEC) indicates that typically a 2% voltage drop is acceptable but any more than that and you're wasting power. Accroding to the chart, using 12awg, at 20Amps load would result in a 2% voltage drop every 35'. :eek: Crap that's almost a 3rd of my required length-If I am calulating this correctly, I'd end up with a drop of about 5.14% or a 6.12V drop-from a 120v start I'd have only 113.83v for my HT.
I might be better off with 10awg, but that would put the length at 55, still almost half with a Vdrop of 3.27% or 3.92v=116.08v.
I'd have to run 8awg cable to get a full 20 amps at 90' before getting a 2% VDrop (2% or 2.4v=117.6v).
However I'm assuming that vdrop is based on 20amps in use so I figure with the max draw on the HT is about 11 when cranked and that's usually not steady, so looking at the chart for a 10 amp load with 12awg, the lenth for a 2% VDrop is now 75' (2.4% or 2.88V=117.12v). Well that's better.
But I'd get 115' with 10 awg at 10 amps so only a 1.57% drop or 1.88v=118.12.
I'll have to look at the costs for the cable to make a better decision. I also need to consider the decreased overall VDrop when running multiwire which I am not sure 10/3 is even available and the book doesn't indicate what improvemnt in Vdrop when running multiwire.

I might, however be reaching the point of diminished returns here-esp since I'll be running a sub panel in the future. We'll see of course I could be overanalysing these numbers as well.
When I get home tonight I'm going to measure the V at the panel and at the existing outlet (which has 14awg now) and see what the actual drop is and take that into consideration.
I just have to decide to proceed with the 12awg multiwire or go 10awg.

mmadden28

Oh yeah, the depot also carries a 12/2/2 wire. Its essentially a cable with two hots, two neutrals, and a single ground. Just thought I'd mention it, not a bad option if your running two completely separate ciruits with no need to worry about which leg of the panel you're on and all in one cable run. Its apparently also used in certain GFCI and AFCI applications.

ben62670

Same ground, same neutral is quieter. Ground loop issues;) I doubt you will see the voltage drop more than 2 volts with 14/2 even at 100 feet. It's more of a guide than a rule:) I have always been told to run on different legs. Like you said a 220 breaker will guaranty this. Even with the 12/2/2 I am not sure you would want to on the same legs.

mmadden28

The chart indicates for 14awg a 2% drop with 5 amps every 90', 10 amps every 45', and 5 amps every 30'

I'm going to check actual values when I get home-I'll try idle and loaded, but based on the guidance, I should expect to see at leasts 4% with 10 amps on my line. But if that chart has conservative values then I'm in good shape.

Sounds like the multiwire option is better all around.

mmadden28

mmadden28 wrote: »

The chart indicates for 14awg a 2% drop with 5 amps every 90', 10 amps every 45', and 5 amps every 30'

I'm going to check actual values when I get home-I'll try idle and loaded, but based on the guidance, I should expect to see at leasts 4% with 10 amps on my line. But if that chart has conservative values then I'm in good shape.

Sounds like the multiwire option is better all around.

All measurements taken with a fluke multimeter/clamp ammeter.
At the panel (at the existing HT circuit breaker)I measured 121.8v
At the HT I measured 120.8v with about 2 amps on the line. So a 1v drop just at low current.
I turned everything on (DVD, TV, Onk 805, XPA-5, sub) and threw in Master and Commander, and set the Onk to 0db and played the canon battle scene in the beginning.
I don't have my SPL metere handy-I'll try to get that reading tomorrow.
At the panel I measured a max draw of 11.4 amps at its max
At the HT I measured 111.7v at its lowest avg around 113/114v.

So based on the start of 121.8v, dropping to 111.7v with 11.4 amps over 14awg at probably about 100', I get a a drop of 10.1v, thats an 8.29% drop :eek::eek:
Well at least now I have some metrics I can compare to when I upgrade the line-see if my lights stop dimming when I power the amp up and see if the voltage drops less.

I forgot, that I have 11.4 amps all on the same line right now. The intention is to split that duty across the two new circuits, so I'll only be running 5 or 6 amps on each line. So that will reduce the drop even more :cool:

I think based on all of that so far, unless I hear better advice otherwise, is that I'm going to move forward with the 12/3 dual circuit. I don't think I need to do 10awg, after all I'm going from a 14 to two 12's, I am not sure what that equates to but I would imagine its greater than 10awg equiv.

gidrah

Pound a piece of re-bar into the ground.

disneyjoe7

I wonder if you're worried about voltage drop when you consider that an AVR / HT setup would vary and not be a consent current flow. So you could have peaks of 15 to 20 amps yes the average or normal draw could be only a few amps at best. Those peaks would dip line voltage, but I hope that those large filter caps in that nice amp gives you the current that base note just asked for.


Now not sure if this is legal so I hope someone crimes in on this one. I think you can use 10/3 split feed a 20 amp receptacle from 30 amp breaker(s) This should be wired so the 2 breakers on separate legs of the panel so a 20 amp draws doesn't overload the neutral wire, but cancels the current out. If not very bad things could happen. :eek:

mmadden28

I'm going to doubt that you can have a 20A outlet on a 30A breaker. And going to a 30 outlet would not allow me to use any fancy power cables. Unless I get a custom cable made to connect to a Juicebox of something. I think I'm going draw a line and limit myself to a 20A circuit-but might do 10awg.

I don't think any of the stuff I have will have any 20A+ dynamic current requirements, although I understand what you're saying- that if one of the lines has a dynamic increase in current, the same dynamic increase in VDrop will occur; I'm hoping that the significant upgrade from a single 15A to 2 x 20A lines splitting the load would be sufficient. The 11.4 amps I got in my testing last night is the max I measured while running the system at 0dB with some heavy and dynamic demands (cannon shots), although I am sure I could go up to the max (+9db? or +18dB) and crank the sub up even more (heck I'll even be upgrading the sub soon too), but those levels would be rare :rolleyes:, and like you said, one would hope that 120000uF, or whatever it is in the XPA-5, would be able to handle the slack for the peaks.:cool:

The Wiring Simplified book (which is a good read by the way-much more informative than any of the typcial wiring books you find that are usually geared toward the homeowner with lots of pictures and such :cool:) indicates that when split-wiring using two hots and sharing the ground and neutral, that there will be no current on the neutral line when both loads are equal, and that only the difference in current between the two will flow on the nuetral.
I'm still trying to grasp that concept, Somebody confiirm or correct this: what I gathered from it is that its not likely that I'll overload the neutral line even if I had both circuits maxed out. At the most if one line was in use and the other was not (20 minus 0), thus no more than 20 amps on the nuetral.. If that were a concern, I would just run two separate lines each with thier own neutral, but since sharing teh neutral actually decreases Vdrop.... I'm thinking that I'll be good with the 12awg, but I keep thinking should I just do 10awg since I'm doing it? 10awg just to have the higher guage and lower potential Vdrop, but I have to see if 10/3 is even avail and if so how much more would it cost.

disneyjoe7

It's something that was a little fussy with me also at first but I then looked at it like this.

If you can have a room with 15 amp outlets say 3 here. Feed from a 12/2 with a 20 amp breaker, that's legal I have them in my house. Now I wondered why that legal, but I understand the rule as a 15 amp outlet can only have a 15 amp device plug into it. I know of people here who do a 10/2 with a 20 amp outlet with a 30 amp breaker, so this falls on the same line as about with the 15 amp outlets / 20 amp breaker 12/2 wiring.

mmadden28

disneyjoe7 wrote: »

....I know of people here who do a 10/2 with a 20 amp outlet with a 30 amp breaker, so this falls on the same line as about with the 15 amp outlets / 20 amp breaker 12/2 wiring.

Like DK stated or clarified from the NEC in his responses to my questions in this thread
Actually now that I reread that thread knowing what I know now-that thread makes so much more sense. :)

If you have a 20A circuit with only one receptacle, that receptacle must be rated 20A. However if you have multiple receptacles on that circuit, each receptacle may be rated at 15A. This would be legal according to the NEC gudance.
So if you take that same logic, and apply it to a 30A circuit, one would think you can do the same with as 20A receptacle. Is that what you're saying?

According to the page from the NEC that DK attached in his thread, in the chart (Table 210-21(b)(3)), I interpret that to reads that a 30A circuit must have 30A rated outlets whether you have one or several receptables on the same circuit. I'm sure the writers of the NEC have some reason for that requirement., and since the NEC is not law, but that local governments have laws the require compliance with the NEC, it may in fact make using a 20A outlet on a 30A circuit illegal, but again, local laws would prevail and you're locallity just might allow it.

Personally though, I wouldn't feel safe knowing that 30A would be required before my shorted 15A device would trip the breaker, possibly resulting in shock or fire.

disneyjoe7

I think you're right, 30A circuit wouldn't be legal if not over one 20A outlet. I never seen it myself, its just what I understood from someone else. Maybe it's was a 20A break circuit with 10g wire with a 20A outlet.

Like I said I'm not 100% on that.



BTW I never seen a break circuit cut the outlet voltage when a 15A device DIED. It just smoked never kick the breaker, if your likely smoke then fire.