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SandShark
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Santa Fe, TX
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Isolated Ground Receptacle (IGR) Question

Can someone explain, in non-NEC-speak, under what conditions one would use an Isolated Ground Receptacle (IGR) as opposed to a receptacle that is not IGR?

Links:

IGR - »www.grainger.com/Grainger/wwg/se···t=subset

Not IGR - »www.grainger.com/Grainger/wwg/se···t=subset
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Jtmo
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Novato, CA

1 recommendation

When you want to insulate a sensitive piece of equipment from anything else in the building. Say a $30000 box that does not have a UPS on it.
Reduce noise in a high noise commercial environment.
Also, who knows if that conduit ground is open up in the ceiling?
Common on sensitive electronics, and also on equipment that the shell is made of metal?
What can cause issues? Transmitting radios, vacuums, motors, heaters, Fluorescent lights, and my favorite fridge or vending machine. Those last 2 are a nightmare in my world.

Overall, give me a good UPS, but that can be expensive for a large piece of equipment.


sk1939
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reply to SandShark
Even if the conduit in the ceiling is open, you should still have a ground wire inside of said conduit connected to the outlet.

Simple explanation is when you have to have a separate ground from the electrical box and/or conduit. Often used in audio applications where the likelihood of picking up noise is high, and the noise is then transfered to ground. Also, these outlets are used in hospitals for applications around things like oxygen and such. You will most often find isolated ground receptacles referred to as hospital grade outlets, and indeed if you visit Lowes, hospital grade will be the only iso ground outlets you will find.

Basically for a home, unless your some kind of audiophile who overpays for almost everything, or running a recording studio/hospital I wouldn't worry about iso-grounded outlets. As aforementioned, they have industrial and commercial uses, but that's really about it.

You'll find varying information all over the internet, here's one example:

The final argument, and the only one sanctioned by the NEC, is that an isolated ground system may reduce electromagnetic noise interference from appearing on the branch circuit. (In fact, the NEC permits the use of an isolated ground system only where required to reduce electromagnetic noise interference; thus, anybody who insists there is any other reason for installing isolated grounding is caught in a Catch 22–and prohibited by the code from installing an isolated ground.)

Large currents in nearby circuits can induce small, unwanted 60-Hz voltages in the grounded raceway of another circuit and the grounded cases of any plug-and-cord equipment. Possibly, some poorly isolated equipment might be sensitive to this–certainly, old-fashioned AC-DC tube-type radios, whose filaments were connected across the AC line.

Another example:

»docs.google.com/viewer?a=v&q=cac···Hd6boq0A


nunya
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reply to SandShark
"Isolated ground" is over-used and very misunderstood. I think the term should be changed to "insulated ground".
Ann older but excellent article on the subject that sums it up much better than I can: »ecmweb.com/mag/electric_pros_cons_ig/

Personally, I think it's a conspiracy by the people who make orange nylon dye.
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sk1939
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said by nunya:

"Personally, I think it's a conspiracy by the people who make orange nylon dye."

LOL. I personally, have not understood why anyone would want to use one at home.


nunya
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I think 99% of IG installations (commercial, industrial, or resi) are done under misguided intentions.

I have two customers, both large national chain stores, who insists on having them installed for their POS and phone systems on every new build.

I only questioned them once. They both demanded / insisted it was necessary. I bid the jobs accordingly and take their money happily.
One of their "architects" even sent me a drawing of how they wanted the separate ground rod installed for the "IG system".
I laughed and laughed. I wonder what the inspector would have thought of that?


sk1939
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Indeed. A recording I do work for just put in an bunch of IG circuits cause of radio interference, but other than that, I can't think of a single commercial use.


SandShark
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reply to SandShark
Thank you all for your well-written and understandable explanations. One other question: would using an IGR receptacle for this commercial appliance provide any additional safety from electrical shock than a properly grounded non-IGR receptacle?



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whizkid3
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2 recommendations

No. It may actually provide less personnel safety from an internal ground fault. If you want to add safety against electrical shock, you will put it on a GFCI receptacle.

For the record, isolated-ground receptacles have nothing to do with electrical safety. Their purpose was to isolate the grounding systems back to the grounding electrode system (of the derived source), in an attempt to reduce electrical noise on the equipment grounding system for sensitive equipment (computers, etc).

For quite a long time, professionals & grounding experts have recognized that isolated ground receptacles did a very poor job at what they were designed for; are not as needed as they once were; and there are much better ways of improving the performance and reducing the noise for equipment that is sensitive to this noise. Isolated grounding receptacles may help in poor designs, where other steps are not understood or not taken; provided the rest of the isolated grounding system is properly designed (it usually isn't.) And they may actually hurt the performance, especially in larger buildings.

Grounding system design for computer & communications facilities is something that I a lot of experience at. I never use isolated grounding receptacles in these facilities. They are not needed and generally do very little to improve performance. You can learn a lot more about this topic if you can get your hands on a copy of the 'IEEE Green Book'.

According to the great link that nunya provided, it would also be a code violation to use an isolated ground receptacle on anything other than electronic equipment. That includes commercial cooking equipment such as your coffee maker:
quote:
any attempt to place an IG-style connection (receptacle or direct connection) onto any other point on the wiring system — or to serve non-electronic equipment with it — is an NEC violation of either 250.146(D), for receptacles, or 250.96(B), for direct connections

Bobcat79
Premium
join:2001-02-04
reply to SandShark
I have IGR and standard outlets in my cubicle, but have been given no guidance on what should be plugged into which.


james1

join:2001-02-26
reply to whizkid3
said by whizkid3:

According to the great link that nunya provided, it would also be a code violation to use an isolated ground receptacle on anything other than electronic equipment. That includes commercial cooking equipment such as your coffee maker:

quote:
any attempt to place an IG-style connection (receptacle or direct connection) onto any other point on the wiring system — or to serve non-electronic equipment with it — is an NEC violation of either 250.146(D), for receptacles, or 250.96(B), for direct connections

An interesting restriction when applied in this day where you can find electronic components rivaling supercomputers of the past in what would have traditionally been a simple electric appliance. Where could they possibly draw the line?

Don't you think that it's possible that the rule you quote is referring to using the wiring for an IG receptacle as a junction to serve additional non IG receptacles?
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ArthurS
Watch Those Blinking Lights
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Hamilton, ON

1 recommendation

reply to whizkid3
said by whizkid3:

Grounding system design for computer & communications facilities is something that I a lot of experience at. I never use isolated grounding receptacles in these facilities. They are not needed and generally do very little to improve performance. You can learn a lot more about this topic if you can get your hands on a copy of the 'IEEE Green Book'.

From my perspective in designing very large scale audio visual systems, properly designed isolated ground systems are NOT optional to maintain the same ground plane for all equipment. This minimizes ground loop problems when the shields are shared between physically separated devices, pretty important especially since amplification of signals can be a millionfold or greater, hence the importance of keep noise floor to a minimum. Hospitals require them for sensitive electronic equipment as well. The problem is that many of the electrical engineers I meet with have very little experience or knowledge on properly designing such a system, and few contractors are meticulous enough to properly implement such a system. Maybe that's why isolated ground systems have such a bad reputation.

I have never heard of an isolation ground power system reducing radio interference in a system, that's normally solved by proper cable shielding and input stage design with the electronics. I will agree that for the most part, isolation ground system are highly overrated for other applications such as POS, computer equipment, copiers, or even home use. Perhaps with computer systems a lot of the current use of isolated ground receptacles is a carryover from the old days of using shielded wiring in data cables. With UTP cable and balanced data lines today, the benefit of iso ground is dubious for such an application.

Both the Emerald and Green IEEE books are good reading on this, but Ralph Morrison's book on grounding and shielding is timeless. Great whitepapers on the topic written by some of the top engineers in this specialization:
»www.audiosystemsgroup.com/SurgeX···ound.pdf
»www.middleatlantic.com/pdf/PowerPaper.pdf


SandShark
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reply to SandShark
Excellent information. Thanks for all your replies.
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John Galt
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reply to sk1939
said by sk1939:

You will most often find isolated ground receptacles referred to as hospital grade outlets...

This is inaccurate.

public

join:2002-01-19
Santa Clara, CA
reply to sk1939
said by sk1939:

Indeed. A recording I do work for just put in an bunch of IG circuits cause of radio interference, but other than that, I can't think of a single commercial use.

Many lab/industrial uses are realized using ultraisolation transformers.


whizkid3
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Queens, NY
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reply to ArthurS
said by ArthurS:

said by whizkid3:

Grounding system design for computer & communications facilities is something that I a lot of experience at. I never use isolated grounding receptacles in these facilities. They are not needed and generally do very little to improve performance. You can learn a lot more about this topic if you can get your hands on a copy of the 'IEEE Green Book'.

From my perspective in designing very large scale audio visual systems, properly designed isolated ground systems are NOT optional to maintain the same ground plane for all equipment. This minimizes ground loop problems when the shields are shared between physically separated devices, pretty important especially since amplification of signals can be a millionfold or greater, hence the importance of keep noise floor to a minimum.

That I understand. Audio systems have different problems than data communication systems. On the other hand - and you know this - there are also other important ways to improve the performance of these types of audio systems. But such audio systems, data communication systems and coffee makers are different subjects altogether.

said by ArthurS:

Hospitals require them for sensitive electronic equipment as well.

Actually, this is quite incorrect. Its quite common for people to confuse the orange hospital grade receptacles with the orange isolated ground receptacles. (In fact there is no longer any requirement for either of these receptacles to be orange. IG receptacles have a green triangle. HG receptacles have a solid green dot.) Hospitals use a completely different system to isolate the conductors (power conductors not ground) from the possibility of a fault becoming lethal for patients. Its not the 'sensitive electronic equipment' that is being protected in hospitals. Its the patients that are being protected. The smallest leakage current can be fatal to a patient. Hospitals use an isolation board at each bed, with isolation transformers and line isolation monitoring equipment. They do not use isolated ground receptacles unless a combination IG & hospital grade receptacle is required for other purposes.

said by ArthurS:

The problem is that many of the electrical engineers I meet with have very little experience or knowledge on properly designing such a system, and few contractors are meticulous enough to properly implement such a system. Maybe that's why isolated ground systems have such a bad reputation.

Surely, the first part is partly true. But its not that the isolated ground receptacles have a bad 'reputation'. Even when isolated grounding systems are designed & installed correctly - while they may help your audio systems - they do not solve the problems in data communication systems that they were developed for. Depending on the impedance of the grounding system, and the coupling between the isolated grounding wire and the conductors (they run in the same conduit), the use of isolated grounding systems can often provide worse performance against electrical noise & transients than a standard equipment safety grounding system. Quite a few methods have been developed for improving noise and transient immunity that far exceed the properties of even a perfectly designed isolated grounding system in the data communications field. There is no benefit to justify their expense. The receptacles do not exist, btw, for quite a number of ampacity and configuration requirements. These reasons are why 'real' electrical design professionals in the data communications field no longer use them.

said by ArthurS:

Ralph Morrison's book on grounding and shielding is timeless. Great whitepapers on the topic written by some of the top engineers in this specialization:
»www.audiosystemsgroup.com/SurgeX···ound.pdf
»www.middleatlantic.com/pdf/PowerPaper.pdf

Thanks for the link. I will try to get a hold of a copy.


cdru
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said by whizkid3:

IG receptacles have a green triangle.

Green triangle? Is that a requirement that it's green? The IG outlet linked to above has a orange triangle, as does the outlet in my cubical. Neither of which has a housing that is orange though.

Bobcat79
Premium
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My daughter's hospital room had receptacles with orange housings. Don't know what that meant.


sk1939
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reply to John Galt
It is, but a lot of times on audio forums you see the terms used interchangeably even if they are different.

Edit: $39 seems steep for an otherwise normal 5-15R outlet. I can pick up an orange iso-ground from H.D for $~10.


John Galt
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said by sk1939:

It is, but a lot of times on audio forums you see the terms used interchangeably even if they are different.

Perhaps it would be best to not perpetuate such practices...


cdru
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reply to sk1939
said by sk1939:

Edit: $39 seems steep for an otherwise normal 5-15R outlet. I can pick up an orange iso-ground from H.D for $~10.

Grainger is almost always the more expensive route if a part has other local sources. But if you need it now, and they are the only source in town...

Another recent thread covered the very same thought too.


cdru
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reply to sk1939
said by sk1939:

Often used in audio applications where the likelihood of picking up noise is high, and the noise is then transfered to ground.

All audiophiles know to use audio grade outlets.


sk1939
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said by cdru:

said by sk1939:

Often used in audio applications where the likelihood of picking up noise is high, and the noise is then transfered to ground.

All audiophiles know to use audio grade outlets.

That thread is full of win, audiophiles are audiophools, and a fool and his money are soon parted. Audio applications I'm referring to are recording studios where we normally dump a whole lot of stuff to ground cause everything is shielded. Even then, mostly we just use normal 20A outlets.


whizkid3
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reply to cdru
said by cdru:

said by whizkid3:

IG receptacles have a green triangle.

Green triangle? Is that a requirement that it's green? The IG outlet linked to above has a orange triangle, as does the outlet in my cubical. Neither of which has a housing that is orange though.

Really don't know. IG receptacles have a triangle, that is certain (while the hospital grade receptacles have a green circle, unless they are green, I guess.) As far as 'orange receptacles' go, at one point in time, both the IG & HG receptacles in the US were orange. They no longer need to be orange for many good reasons. They have the symbols that I discussed.

Here is another good link discussing IG wiring:
»ecmweb.com/grounding/electric_hows_whys_ig/