Isolated grounds

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wireman3736

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I was just wondering how many electricians are installing isolated ground receptacles or circuits for equipment, It seems that back in the 90's there was alot of equipment out there that was specifying an isolated circuit for there equipment, I have to say I don't do as much industrial or commercial that I used to do but I still do some and I can't remember in some time having to install an isolated ground for any equipment. I was told by a pc expert that electronics have come along way and noise in the line isn't as much of a problem as it once was. Does anyone have an opinion on this. Thanks
 
IMO A waste of time and materials.

Even if they where beneficial in most applications they become corrupted by incidental contact with 'non' isolated EGCs.
 
I have to admit more times then not, installations that I have come upon the ground only went to the subpanel and not back to the main, sometimes there were 2 or 3 panels in the line.
 
I know what you mean. Some people are under the impression that the isolated receptacle itself is the only requirement. Others don't realize than NM and plastic boxes do the same thing, except for the landing-in-the-subpanel issue.

On the other hand, we're finishing up a restaurant where IG was spec'ed for the POS terminal system and server. I used 12/3 MC and stripped the red to use as the EGC, and the green as the insulated conductor for the IG receptacles.

Cheating? Maybe, but the inspector had no issue with it.
 
And if the chassis of the POS equipment contacts any stainless steel counters all your work will be for nothing....:D

BTW many would say that is a 250.119 violation.
 
iwire said:
IMO A waste of time and materials.

Even if they where beneficial in most applications they become corrupted by incidental contact with 'non' isolated EGCs.
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I could not agree with this more.

Does anyone know what the purpose of the IG is/was? I was under the impression (but do not know for sure) that back in the 70's electronic equipment used the ground in some of their communication circuits and it caused havoc when some AC equipment had some faults to ground. The IG was an effort to isolate the electronic equipment from this.

Anyone know how/why it all got started?
 
Computers are still sensitive to ground "noise". The trend of less usuage of isolated receptacles is the fact that some were not installed correctly, as has been mentioned and they are easily corrupted, and they are using other technology.

The place I see isolated circuits used most these days is for registers, by means of installing isolation transformers. I still see the lack of understanding in the field by some installers who do not quite get the concept and will inadvertently mix isolated and non-isolated circuits in some installs.
 
I'm sorry but if the electronic equipment requires the use of isolation transformers and or isolated grounds it is poorly designed equipment. This is just like the electronic people complaining that harmonics on the electrical system causes problems for their equipment...but most of the harmonics are created by their equipment. Why should the electrical system have to be changed to cover the design problems of the electronic equipment?
Don
 
An isolated ground is a good patch for bad installations. If the isolated ground is run back to main service and by-passes one or more sub-panels that have been installed with incorrrectly connected grounds and neutrals, then they may be of benefit. If the isolated ground is only run to the sub-panel, then there is no benefit. If the sub-panels are installed correctly with isolated neutrals then there is little or no additional benefit in installing isolated ground receptacles.
 
I'm installing some on my current job, but not for the equipment that's being plugged into the recepts. They're located in a telephone CO in the kickspace of the equipment racks. They don't want the metal ears on the recept to come in contact with the frame. So my installation is PVC with Carlon plastic boxes and IG recepts. My light fixtures are also not allowed to touch the cable racks above, so they're mounted on fiberglass strut and piped with PVC.
 
At least we finally weeding out the people who think an IG recep should be connected to a ground rod.

The word ISOLATED was probably the worst choice to name this installation.
 
The isolated ground was never intended to eliminate "power line noise" but rather to prevent ground loops which affected the data communications..

Isolated grounds are typically a waste of resources, now that devices are more self contained and the use of shielded (especially at both ends) data cables has been all but eliminated.

Part of the original reason for the dedicated/isolated ground was the interconnection of CPUs, printers, disk drives, terminals and other components. In the old days these were spread around a facility and the power conductors were often connected to different ground paths, but the dedicated shielded data cables interconnecting all of these devices created multiple ground paths and "stray" currents which in turn corrupted the data signals.

There may be nothing wrong with only bringing an isolated ground back to a sub-panel. The intent is really "single point" grounding so it usually makes no difference where the point of common coupling occurs. An ideal grounding system for communication cabling is a star design (everything radiates from a single point) rather than a daisy chain (where the conductor loops from one device to the next). This is why the interconnect automation devices in an industrial system have dedicated grounding points in each control cabinet. An ideal grounding system for communication cabling is a star design (everything radiates from a single point) rather than a daisy chain (where the conductor loops from one device to the next).

Again, IMHO, if a spec calls for isolated grounds it is most often a case of the specifier more interested in CYA and therfore just doing what they've always done, rather than keeping current with technology.
 
LarryFine said:
In that case, I'd respond by quoting 250.119(B)(1).
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Larry I am well aware of that.

And although I have done the same thing you describe (use 12/3 for IG) IMO the inspector would be well within there discretion to say no way.

Do you really think a typical restaurant fits 250.119.(B)?

"the conditions of maintenance and supervision ensure that only qualified persons service the installation"

Who is the supervision, the line chef? ;)
 
Allow me to jump in here folks. I have done a lot of work with IGR since the late 70?s and might be able to shine some light on the subject.

First, the IGR is only intended as a possible means of obtaining common-mode electrical-noise reduction on the circuit in which it is used. It has no other purpose. If the feed already has common-mode noise problems, the IGR cannot remove it, only an isolation device like a transformer or UPS can do that.

The IGR came about in 70/80?s time frame when banks and data processing started popping up. In those days all I/O port communication used an unbalanced form of communication like RS-232 where ground was used as a signal path. The common signal ground was connected to the EGC. As most of us know minute currents are injected into the EGC from nearby phase conductors which cause voltage differences along the EGC paths. These voltage differences are felt on the bit detectors and if large enough can cause errors in the detectors. Another example is hum on PA systems that is heard.

Well the days of RS-232 and all unbalanced signal transmission are gone. All modern communications today is balanced like Ethernet or optical, making IGR antiquated. I have not worked with any of the POS equipment and do not know why they are requiring IGR, maybe someone will enlighten me.

Someone mentioned IGR in telephone offices which is a horse of a different color. Telco use isolated single point ground for power supplies and equipment grounds. This is done for completely different reason, like eliminate out side fault currents (lightning, shorts) from flowing in the isolated ground plane. However I can tell from the description the poster stated is a misused application, is completely worthless, and likely to cause more problems than will be eliminated.

For example running the AC circuit from a remote source in PVC and isolating the box from the equipment rack. Once equipment is installed in the equipment rack uprights, plugged into the socked, the IGR is violated. This is not the correct use of the application.
 
Wouldn't having a longer ground path give less chance for short circuit protection? Meaning usually isolated grounds are run back to the main e.g .bonding point.Resistance of conductor,ect.

Bob O.84,Pa.
 
I might be able to shed a little light on this. There is still some newly installed POS (point-of-sale) equipment that uses either RS-232 or RS-485 for their inter-device communications.

Example:
The local fast food resturant, with it's terminals at the various stations (fry, drink, sandwich, register...). Instead of using smart equipment at these stations (b/c there really isn't that much going on at each one), you use a dumb terminal that communicates back to a single server (with a lot of serial connections) that directs all of the communication. Well all of those RS-232 lines bond the reference (ground) conductor of the communication circuit to the EG for the connected device (at both ends), as mentioned earlier by Bob (iwire).

The reason that POS equipment hasn't had to evolve (generally speaking), is because the information bottleneck wasn't the communication medium, but instead the terminating equipment (one person can only hit the "Big-Mac" button so fast, and the serial port had more than enough bandwidth to keep up.) The equipment didn't have to be pretty or offer a friendly interface, it just had to work and a serial connection was all the bandwidth that was needed. So why re-design to support a higher bandwidth connection?
 
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