Isolated Ground Receptacles

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dvcraven052256

Member
Location
St. Louis, missouri
Occupation
Electrical Engineer
I have a project where isolated ground receptacles are call for from the AV engineer. They eliminated the ISO transformer because of cost but the IG receptacles remain.

Frankly I don't understand the use of IG receptacles. In essence all goes back to the N-G connections at the transformer or service anyway so do you really gain anything the IG devices.

I look forward to any comments.

Dan Craven
Kaemmerlen Electric
 
IG receptacles are pretty much obsolete especially if there is no design to support how they're supposed to be set up. They should terminate at the X0 or the service where the MBJ is installed. Absent that they're a waste of money.
 
dvcraven052256 said:
Ok, but it all goes back to the main grounding electrode system, so I don't understand what advantages it provides.
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There is only a single connection point which is either at the service or the X0. All other points on the system (metal boxes, raceways, etc.) have no connection to the IG
 
dvcraven052256 said:
Yes, I understand. So, I guess what you are saying is there may be some interferences that could be avoided via boxes or raceway along the way. Is that correct?
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Yes, or from other grounded items on the same branch circuit or feeder (why is the elevator motor on the same feeder as my IT room!!!). I think the main use of these is from the old days of IT when computers would glitch and the manufacturer would say you have bad grounding or noisy grounds because they didn't really know what was wron or they didn't experience the problem. That buys them time while you go retrofit your IT rooms with IG circuits and receptacles. Then the problem still persists or maybe because it was random it happened to go away or it went away with a software update, but then someone says the IG fixed it.

Our computer lab spent so much money on dedicated circuits with IG receptacles, transformers in each IT room, and finally double conversion UPSs.

Video guys will see it issues too with ground loops and coax cable. This is especially true of the opposite ends of the cable are from equipment on different transformers. We used fiber-optics for a lot of room to room and building to building connections with old unbalanced signals like baseband video, audio, and even RS232. I don't think an IG helps this, but they just hear ground loop and think it will help.
 
In audio and video equipment, it's important to have only one connection to chassis ground in each piece of equipment to prevent the introduction of hum and noise leakage currents that normally circulate in the electrical grounding system. In the same way, giving the a/v equipment an isolated ground may help reduce the leakage currents from other equipment by adding a small, but significant amount of impedance (resistance) to the ground system between the equipment and the bond, because the closest ground bond to other loads or building steel is now way back at the service entrance. These leakage currents are normally on the order of micro- or picoamps, but, it can be enough to deteriorate signal quality if they co-mingle or add up. You may even find that the order of connections at this main ground bus bar, makes a difference in the size of noise currents seen or heard in the a/v equipment.

By the way, this diagram is lacking a return wire for the neutral current to get back to the center of the wye transformer.
 
dvcraven052256 said:
Ok, but it all goes back to the main grounding electrode system, so I don't understand what advantages it provides.
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data or signal circuits that have a ground reference can have undesirable voltage/current on them.

Back in 80s and 90s this was a problem with data. Back then cables between hardware items often had shielded cable between them. Data errors supposedly were less if you ran IG with the power conductors.

These data problems mostly disappeared when UTP network cables became standard or even USB cables for short distances to nearby peripheral items.

Sound and video- often have a grounded conductor as part of that signal circuit, you don't want it grounded at more than one point, though IG with the power conductors really won't resolve most those issues IMO the signal circuit needs some isolation from the power circuit is the best thing. Biggest issue is when one component is powered separately from another and there is also a signal cable between the two components, that is where you possibly get unwanted current circulating through signal cable then over grounding/grounded power conductors to make the loop back to the signal cable again.
 
Isolated grounding, or more appropriately single point grounding, reduces or prevents ground loops. Ground loops can interfere with low voltage signals. This was a big problem back in the day of computers and their peripheral devices communication over cables that used ground as part of their data circuit, like RS232C and printers.
 
jim dungar said:
Isolated grounding, or more appropriately single point grounding, reduces or prevents ground loops. Ground loops can interfere with low voltage signals. This was a big problem back in the day of computers and their peripheral devices communication over cables that used ground as part of their data circuit, like RS232C and printers.
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Problem was when signal/data design people thought it would be good thing to introduce a second grounding point for their signal/data circuits, then do the same thing on another piece of equipment that has to exchange some sort of signal to the first piece of equipment.
 
dvcraven052256 said:
I appreciate all the detail response's.

Based on what I have read IG receptacles is not the cure-all but it does eliminate some electrical noise issues.
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If you run an IG conductor through say metallic raceway and only connect to the EGC terminal of the IG receptacle. I seen times where people installed IG receptacles on NM cable - if the circuit in that instance originated at the service equipment and the receptacle is in a non metallic box, kind of pointless, a regular receptacle is just as isolated in that situation.
 
kwired said:
If you run an IG conductor through say metallic raceway and only connect to the EGC terminal of the IG receptacle. I seen times where people installed IG receptacles on NM cable - if the circuit in that instance originated at the service equipment and the receptacle is in a non metallic box, kind of pointless, a regular receptacle is just as isolated in that situation.
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I've done exactly that for circuits my home music studio. Even with a standard receptacle as long as there's a mon-metallic box you've created an IG circuit.
 
infinity said:
In 2025 I'm doubtful that it makes any real world difference because the equipment that benefited from IGs 20-30 years ago no longer exists.
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Ground loops can still be an issue particularly in industrial plants with remote devices using media like Modbus and RS422/RS485. It is hardly ever a problem in general commercial environments.
Engineering firms do not like to remove things from their specs even when they are not needed 99.999% of the time.
 
Problem also is that most ECs and engineers don't understand IG to begin with, and it gets installed such that it's the same as non-isolated ground making it useless for the intended purpose. They seem to think that you can just daisy-chain the IG conductor from IG receptacle to IG receptacle and back to the EGC bus in a sub panel- no different than the normal EGC.

Each IG receptacle must have its IG conductor home run back to the EG bus in the main panel. Try that on the 20th floor of a building. At least home run them back to the originating panel EG. But they must be home run.

In that diagram above, that IG receptacle is one location. Just figure adding as many as you need in exactly the same way sharing only the same breaker.

-Hal
 
hbiss said:
Each IG receptacle must have its IG conductor home run back to the EG bus in the main panel. Try that on the 20th floor of a building. At least home run them back to the originating panel EG. But they must be home run.
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Actually each ground needs to go back to a source collection point, like a panel, that collection point can then be brought to a another collection point such as the GES. Each transformer starts the isolated ground system over again. It is not much different than how we do feeders and dedicated single outlet branch circuits.
 
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