Isolated Ground.......

[lefty321546]

I have done it once, but other then that dont understand why whats the point. 2 grounds Jw the logic behind it i guess.

 

[LEO2854]

I have done it once, but other then that dont understand why whats the point. 2 grounds Jw the logic behind it i guess.

Welcome to the forum

Take a look at this....

 

[infinity]

I have done it once, but other then that dont understand why whats the point. 2 grounds Jw the logic behind it i guess.

The point is that the IG is connected at only one point in the system, the same point where the main or system bonding jumper is installed. If that really makes any difference is open to debate.

 

[big john]

I have done it once, but other then that dont understand why whats the point. 2 grounds Jw the logic behind it i guess.

The argument is that having an isolated ground reduces common-mode noise that could interfere with electronics.

I've seen a lot more screwed up and inoperable IGs than I have ones that were correctly installed, and I have never seen a problem caused by the fact that a power circuit did not have an isolated ground. My personal opinion is they have basically no practical purpose.

Often they are used as band-aid repairs because there is neutral current flowing improperly on the grounding system.

 

[mbrooke]

If you have no wiring errors in the branch circuits or feeders an isolated ground is not needed.

 

[lefty321546]

Makes scence, I can see were its still one of those debatable things... Thanks

 

[iwire]

If you have no wiring errors in the branch circuits or feeders an isolated ground is not needed.

Or any EGC under those conditions.

 

[dereckbc]

My 2-cents worth since this is kind of my area of expertise. Text Book answer:

IG is only intended to be used as a possible means of obtaining common-mode electrical-noise reduction. It has no other application and its effects are inconsistent. Results vary from; no change, worse noise, or desired result with the first two being most likely when compared to solid grounding (SG). IG is only applicable to metal enclosed raceways. Non metallic wiring systems are by their nature IG. So if you are using NM. plastic pipe, and plastic boxes like you would in a house is an IG circuit by definition.

What is IG suppose to do? Prevent common-mode noise. Truth is that is pretty much BS, because at best the only thing it can really do is help to not make it worse. IT CANNOT remove common-mode noise period. So how does common-mode noise get in the wiring? Real simple, from daisy chained branch circuit, and upstream connected devices injecting noise in the EGC circuit. Cable has capacitance and over long runs the capacitance between Line and Ground and be great enough you leak line current into the EGC circuit. Additionally device like stereos, radios, computers, etc have filters installed between L-G and N-G for FCC compliance purposes that leak line current into the EGC circuit. Those currents can add up and cause minute voltage differences along the length of the path.

How does that become a problem. Well let's use the most common one all of us know, line hum in audio amplifiers. Imagine for a minute we have a centralized Audio Amp with several line inputs from various devices. All the input devices are powered by two or more branch circuits and use a ground referenced signal topology like coax which is unbalanced using Ground as part of the signal path. Because the Audio Amp injects a small amount of current into the EGC, and a small amount of voltage is developed on the EGC between the amp and the N-G bond at the service entrance. Now we input a audio signal that is powered from a different branch circuit, and this that equipment EGC is at a different potential than the Audio Amp. The Audio amp sees that as a 60/120/180 Hz signal and amplifies it. Now you got HUM.

So now let's put this knowledge to good practical use and how you can effectively apply it to make you some extra money and actually give your customer his money worth that works.

1. If this is a stick built house and your customer has high-end AV equipment or Office, simply run a Dedicated 20-Amp, SG, Quad or Standard Receptacle for each area with sensitive equipment. That is pretty cheap and extremely effective. By all definitions an IG circuit that only uses 3-wires (NM 2-wire + G). If they want high-end use a receptacle with built-in TVSS, RJ-45, CATV coax, and Telco POY's line. Basically a built-in surge protector power strip.

If they want really high-end and can afford it here is what I have at my home office and AV system. Run a dedicated 3-wire (L-L-G) 240 volt 20 or 30 amp circuit and one of the high-end isolation transformers with built-in Surge Protection for power, and I/O lines like CATV, Telephone, Ethernet, etc... This is what is known as a Balanced Circuit meaning no grounded circuit conductor aka Neutral. Unbalanced grounded systems are the root cause of all electrical noise problems. We really screwed up in the USA using 240/120 single phase topology.

2. In a commercial building like in an equipment room where there is a lot of data and phone equipment use an Isolation Transformer and run dedicated standard SG branch circuits from the transformer. Even a regular dry type isolation transformer has at a minimum 60 dB Common-Mode Noise Rejection (CMR), and specialized ferroresonent transformers go as high as 120 dB CMR. What you are doing is creating a new low noise ground reference point with the N-G bond.

OK after having said all this, today it is kind of a moot point. Reason being is today we have moved away from using ground referenced signal transmission like RS-232 and other typologies that use ground as a signal path. Today we use fiber and balanced signal transmission like Ethenet that eliminate the problems.

OK I am done now. :blink:

.

 

[mbrooke]

Or any EGC under those conditions.

Please elaborate further... :blink: Not having any EGC would be a code violation.

 

[iwire]

Please elaborate further... :blink: Not having any EGC would be a code violation.

If there are no faults or errors in the wiring there is no safety reason for an EGC. Just like if there are no faults or errors there is no need for OCPDs.



I think we are all well aware they are code required.

 

[mbrooke]

If there are no faults or errors in the wiring there is no safety reason for an EGC. Just like if there are no faults or errors there is no need for OCPDs.



I think we are all well aware they are code required.

I think what your saying is redundant for the sake of the argument.

My point is that if you do not have a code violations like standing ground faults an IG is not needed.

 

[GoldDigger]

I think what your saying is redundant for the sake of the argument.

My point is that if you do not have a code violations like standing ground faults an IG is not needed.

On the contrary, you can have small contributions to current on the EGC, such as equipment with EMI filters that put capacitance from line to ground, that add up to enough current on the EGC to cause enough voltage to make a hum problem on audio gear that uses a single ended input.
If all of the participating devices are connected to IG receptacles, then they will only have to deal with the small amount of current that they put on the EGC and the problem will be reduced. Otherwise the small offset voltages can build up through the entire branch and feeder system.
Some might consider such noise filters and surge suppressors to be standing ground faults anyway, but UL and NEC do not seem convinced of that.

 

[iwire]

I think what your saying is redundant for the sake of the argument.

My point is that if you do not have a code violations like standing ground faults an IG is not needed.

And obviously I disagree.

I have absolutely no idea why you feel code violations determine the need for an IG.

 

[GoldDigger]

And obviously I disagree.

I have absolutely no idea why you feel code violations determine the need for an IG.

Possibly because only a device fault or an extra bond will cause really large currents in the EGC. However you and I agree that smaller currents can count too.

 

[mbrooke]

And obviously I disagree.

I have absolutely no idea why you feel code violations determine the need for an IG.

In no way do I feel or am I advocating code violations be allowed in conjunction with the use of IGs.

What I am saying, is that if you had a code violation such a grounded neutral you will have audio hum or aka a dirty ground. People will notice that.

In the real world issues arising from dirty grounds have fomented the preference for an IG receptacles in an effort to eliminate ground loops. What no one was told was that dirty grounds were caused by wiring errors (NEC code violations).

If you don't have code violations you wont have ground loops, if you don't have ground loops you don't need IGs. Its that simple.


That is what Big John was saying and I am saying the same thing. I am not sure why you are skeating around that.

 

[mbrooke]

On the contrary, you can have small contributions to current on the EGC, such as equipment with EMI filters that put capacitance from line to ground, that add up to enough current on the EGC to cause enough voltage to make a hum problem on audio gear that uses a single ended input.
If all of the participating devices are connected to IG receptacles, then they will only have to deal with the small amount of current that they put on the EGC and the problem will be reduced. Otherwise the small offset voltages can build up through the entire branch and feeder system.
Some might consider such noise filters and surge suppressors to be standing ground faults anyway, but UL and NEC do not seem convinced of that.

You may have a point here, but being honest that generally holds true for exceptionally sensitive and I dare say possibly dated audio equipment. Though there is nothing wrong with some older audio equipment, it still rocks on!

And yes, leakage current for suppressor is not an NEC concern, in fact they have occupancy censor that leak to ground a bit, but there is no limit to how many you can have on a circuit. Im sure that leaking will add up.

EMI filters and surge suppressors do leak to ground, but not the degree a grounded neutral or 3 wire subpanel does.


But here is the deal, as soon as the equipment touches anything else that's grounded like a rack or its connected through shielded cables to other equipment you loose that IG. A true IG application would not only need an isolated ground from the service disconnect or SDS, but all the equipment its connected to would need to be isolated on rubber supports away from anything else grounded. A true iso ground is rare if not impossible to achieve.


Consider cash registers in super markets. Yes, they like to spec an ISO ground. But as soon as the register comes in contact with the stand grounded through a regular EGC with a motor, light ect and other branch circuits forget about it. At this point you are wasting copper. In fact Id say 99% of applications don't need them. And its not like manufactures make the same equipment like they used. Manufactures have figured out, that regardless of ISO grounding or plain jane vanilla outlets people have everything but a clean ground. Equipment today, even sensitive electronics are fare more tolerable of dirty grounds because lets face it few buildings have them.

IGs are only popular because some people believe that ground rods soak up electrons, so an IG is like an express high way to ground soaking up the extra what ever. That's not the case at all. Its just seemed that way because people were running them to straight ground rods rather than the service breaking the ground loop. Further, some people think if it has that special orange color it must mean something really special so to say.


From this paper:

http://www.solacity.com/docs/erico - practical guide to electrical grounding.pdf

"(12) In particular, no attempt must be made during or​

after installation to separate the electronic system?s​

equipment grounding conductors from the ac power​

system?s equipment grounding conductors and its​

associated earth electrode grounding connections.​

Such separations would violate the NEC and​

produce potential electrical fire and shock hazards.​

They would also be likely to damage circuits inside​

the related electronic equipment, or to at least​

degrade the operation of it.​

(13) Note that the use of the IG method even if it follows​

NEC requirements, does not always improve the​

performance of equipment. In fact, the use of the​

IG wiring method is just as likely to make things​

worse or to result in no observable change to the​

operation of the equipment. There is usually no way​

to predict the benefits if any, of isolated ground​

circuits except by direct observation and​

comparison between solid grounding (SG) and IG​

methods in each case.​

(14) It is relatively easy to convert existing IG circuits to​

SG circuits on an as-needed basis. On the other​

hand, it is generally both impractical and not cost​

effective to convert an existing SG circuit to an IG​

style that conforms to NEC requirements.​

Accordingly, circuits used to supply power to​

electronic equipment can be designed and first​

installed as IG types, so that they may later be​

converted back and forth between IG and SG as​

needed."

 

[mbrooke]

Missed the link, my bad, from ET:

http://www.electriciantalk.com/f2/practical-guide-grounding-bonding-72465/

 

[iwire]

Let me start off with saying I think IGs are a waste of time and materials in almost all cases.

I only install them because I am paid to install them.

You may have a point here, but being honest that generally holds true for exceptionally sensitive and I dare say possibly dated audio equipment.

Why only 'dated audio equpment' what has recently changed?

Though there is nothing wrong with some older audio equipment, it still rocks on!

As do I.

And yes, leakage current for suppressor is not an NEC concern, in fact they have occupancy censor that leak to ground a bit, but there is no limit to how many you can have on a circuit. Im sure that leaking will add up.

EMI filters and surge suppressors do leak to ground,

And that can cause issues on audio lines yes?

but not the degree a grounded neutral or 3 wire subpanel does.

Glad you know that.

But here is the deal, as soon as the equipment touches anything else that's grounded like a rack or its connected through shielded cables to other equipment you loose that IG.

Another news flash, thanks. (Not trying to be disrespectful, just having some fun)

The above is one of the top reasons I think IGs are a waste of time. In most circumstances they often become compromised soon after completion.

A true IG application would not only need an isolated ground from the service disconnect or SDS, but all the equipment its connected to would need to be isolated on rubber supports away from anything else grounded. A true iso ground is rare if not impossible to achieve.

I have yet to see anything more than opinions on what a 'true IG is'. I sense your definition is pretty narrow.

Consider cash registers in super markets. Yes, they like to spec an ISO ground. But as soon as the register comes in contact with the stand grounded through a regular EGC with a motor, light ect and other branch circuits forget about it. At this point you are wasting copper. In fact Id say 99% of applications don't need them.

We are in 100% agreement. :thumbsup:

 

[iwire]

What I am saying, is that if you had a code violation such a grounded neutral you will have audio hum or aka a dirty ground. People will notice that.

Yes, but that is not the only reason and you can have a dirty ground. Your position seems to be that only code violations induce hum on audio lines. I disagree. Any AC current flow on the shild between audio equipment can be a problem and IGs can sometimes help to reduce that current.

In the real world issues arising from dirty grounds have fomented the preference for an IG receptacles in an effort to eliminate ground loops. What no one was told was that dirty grounds were caused by wiring errors (NEC code violations).

Do you have a source for this or is it just what you have decided?

If you don't have code violations you wont have ground loops,

And I still disagree with that assessment.

That is what Big John was saying and I am saying the same thing. I am not sure why you are skeating around that.

I am not 'skeating' around anything. I simply disagree with your position that the only cause of ground loops are code violations.

 

[dereckbc]

If you don't have code violations you wont have ground loops, if you don't have ground loops you don't need IGs. Its that simple.

That is not factually correct. Simply connecting your CATV, SATV, or aerial antenna creates a loop. Interconnecting audio device with ground referenced signal inputs creates loops. All those interconnections fully comply with NEC requirements. No IGR can fix it or remove the problem, most likely is does nothing or make it worse

Move into a commercial or industrial installations and the whole building has thousands to millions of ground loops. In those installations the building is made from steel and concrete and every place you attach conduit, junction box, machinery, makes contact with the structure you have a loop. No amount of IGR is going to fix any of that.

Like I said earlier IGR today is a 8-track tape issue and completely antiquated because today almost no signal interconnects today use unbalance signal transmission they use ground as a signal path. If you have some relic equipment using something like RS232, you do not use IGR to fix noise problems. You get you a pair of optical isolator and fiber cable to replace the antiquated copper signal cable, or convert to Ehternet or some other form of Balanced Signal transmission.

Today in a modern Telephone Offices, Data Centers, Cell Tower, and Communication Centers the whole building is designed to be a massive ground loop where you intentionally bond everything together with copper straps. It is called MESH GROUNDING. Some of the equipment is required and installed on steel diamond plate decking on a raised platform. Next time you drive by a cell tower and the carrier uses outdoor equipment take not it is on a raised platform of steel. They are constructed much like a electrical sub-station. That raised platform is bonded to earth every 4 to 6 feet and each corner to another underground grid type GES. The whole purpose of doing this is forming a Equipotential Ground Plane where the impedance between any two points is practically ZERO. So any currents that might be passing through it does not produce and significant voltage including lightning fault current.

Ground Loops are good thing to have if you know what you are doing. Single Point Ground can be used, but is easily compromised even following NEC requirements.