Isolated Grounding

11154 Views 28 Replies 13 Participants Last post by brian john, Dec 15, 2009

beartard

Discussion Starter · Oct 31, 2007

This is something that has always baffled me (and, it would seem, lots of others older than I am, judging from the various ways I've seen it done.) A lot of my work lately has been tenant buildouts in shopping malls. The mall supplies 480V 3PH metered power to the spaces, and we install new transformers in each space. Almost all tenants specify IG receptacles for cash registers, kiosks, and other computer locations. I'm gonna show some ignorance and ask the following for the gurus:

1) What 'earthly' good is isolated grounding?

2) If stores need them, why wouldn't I in my home?
Theory: harmonics from fluorescent ballasts affecting data somehow?

3) Does the IG electrode conductor (my term) stop at the transformer feeding my new service, or does it go all the way back to building steel?

4) Does it have to attach to both building steel and a water line?

5) If instructed to place both the transformer's GEC and the IG conductor through the same hardware on the building steel and water line, is it really isolated?

and lastly

6) In a retail situation like this, with everybody connecting their respective grounds to the same structures, is it even possible to have "isolation"?

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brian john

· #2 · Oct 31, 2007

1) What 'earthly' good is isolated grounding?

In a properly installed electrical system NONE< in an improperly installed electrical system, MAYBE SOME. Improperly installed in this instance refers to downstream neutral ground connections.

2) If stores need them, why wouldn't I in my home?
Theory: harmonics from fluorescent ballasts affecting data somehow?

In a single phase system triplen harmonics are not an issue, and unless the store has tons of electronics, (Best Buy etc.) harmonics are most likely not an issue, in either case the IG has nothing to do with this.

3) Does the IG electrode conductor (my term) stop at the transformer feeding my new service, or does it go all the way back to building steel?

At the XO in the transformer from that point it should be isolated from other grounds (in most installations this is not the case)

4) Does it have to attach to both building steel and a water line?

NO see above.

5) If instructed to place both the transformer's GEC and the IG conductor through the same hardware on the building steel and water line, is it really isolated?

Sure from XO to electrode you have parallel paths, it is from XO downstream they need to be isolated.

6) In a retail situation like this, with everybody connecting their respective grounds to the same structures, is it even possible to have "isolation"?

Has nothing to do with anything, if you keep the separately derived systems SEPERATE. No crossed neutrals which is common, unfortunately.

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beartard

Discussion Starter · #3 · Nov 2, 2007

Thanks for the answer. In my experience, it seems that customers ask for isolated-ground receptacles when what they want is a dedicated circuit for a piece of equipment (and mainly a pretty, orange receptacle.)

What I'm usually asked to do is run IG wire from each device to the low-voltage panel IG bar, then from there *through* the transformer to building steel and a water pipe, bypassing X0 altogether. It seems to me that such an installation could cause more trouble than good if noise is a problem.

I've even had one installation where the plans called for the Isolated GEC to go to its own driven ground rod, not bonded with the regular house system. I didn't think that was legal either, but the engineer supposedly knows what he's doing, right?

I'm an installer...one day I hope to be an electrician.

brian john

· #4 · Nov 2, 2007

Isolated GEC to go to its own driven ground rod, not bonded

WRONG, WRONG, WRONG oh did I mention this is WRONG.

IG to the XO in the transformer, seperate electrode is a NEC violation.

JohnJ0906

· #5 · Nov 3, 2007

beartard said:
I've even had one installation where the plans called for the Isolated GEC to go to its own driven ground rod, not bonded with the regular house system. I didn't think that was legal either, but the engineer supposedly knows what he's doing, right?

ALL Equipment grounding conductors MUST end up at xfmr X0, or it can't do it's job - i.e.: Providing a low impedance path for fault current to allow the OCPD to operate.

I'm an installer...one day I hope to be an electrician.

Keep asking questions! :thumbsup:

Old Spark

· #6 · Dec 4, 2009 (Edited)

NEC 250-146D, Explains the Isolated Ground somewhat. The Isolated Ground is not a cure all, but it can help clean up noise. I like some of the suggestions by the guys who have made comments. Dedicated circuits, dedicated neutrals, oversize neutrals, with Isolated Ground can help a lot. We use them on cash registers, tank monitoring systems, phone board, plus computers. Our engineers tell us that the Isolated Ground buss (isolated from the panel cabinet) must have a separated ground wire all the way back to the MSB, the first panel fed by the transformer.
--------adder
In the case where you have a stepdown transformer from 480 to 120/208, the iso. ground does go to the XO at the transformer,not the SMB. (we seldom have a system that doesn't start and finish with 120/208 so the only transformer is the utility transformer) Our work is almost intirely gas stations, so we don't get to work with 480/277 much. Hope to get to soon.

mattsilkwood

· #7 · Dec 5, 2009

A ground is a ground is a ground. An IG is just another wire in the pipe.

RIVETER

· #8 · Dec 5, 2009

Grounding

brian john said:
In a properly installed electrical system NONE< in an improperly installed electrical system, MAYBE SOME. Improperly installed in this instance refers to downstream neutral ground connections.

In a single phase system triplen harmonics are not an issue, and unless the store has tons of electronics, (Best Buy etc.) harmonics are most likely not an issue, in either case the IG has nothing to do with this.

At the XO in the transformer from that point it should be isolated from other grounds (in most installations this is not the case)

NO see above.

Sure from XO to electrode you have parallel paths, it is from XO downstream they need to be isolated.

Has nothing to do with anything, if you keep the separately derived systems SEPERATE. No crossed neutrals which is common, unfortunately.

I am here to learn and to possibly give information. GROUND is in reference to EARTH. I don't understand WHAT an isolated ground can even add to better the problem. Any time that a magnetic field crosses a conductor that IS a closed loop, current will be induced. In the case of a grounded conductor...GEC,
it does the same and is dissipated. Spikes are caused by weird stuff like lightning strikes...battery chargers...and just plain faulty equipment. If I had a sensitive piece of equipment that I was concerned about I would run a totally independant circuit and pray...because it still happens.

RePhase277

· #9 · Dec 6, 2009

RIVETER said:
I am here to learn and to possibly give information. GROUND is in reference to EARTH.

Not really. When an electrician says ground, 99% of the time they are referring to something tied to a designated electrical zero point. In the vast majority of systems, this is the neutral point. And in electronics and automotive electrical, ground is mentioned continuously, with no connection with the earth.

Old Spark

· #10 · Dec 7, 2009

We are talking about separate grounding conductor back to the MSB, not the neutral. The isolated ground (ing) must be a separate conductor, insulated, and makes no contact to a grounding source except at the isolated ground buss and the main ground buss at the ufer.

Bob Badger

· #11 · Dec 7, 2009

David Channell said:
We are talking about separate grounding conductor back to the MSB, not the neutral. The isolated ground (ing) must be a separate conductor, insulated, and makes no contact to a grounding source except at the isolated ground buss and the main ground buss at the ufer.

I do not see what the Uffer has to do with it, ideally the IG conductor would terminate at the same buss the system bonding jumper is located at. Either XO at a SDS or at the service panel in a building without SDSs.

Old Spark

· #12 · Dec 7, 2009

Out here the ufer is landed on a ground buss in the MSB and that buss is bonded to the neutral buss. So all grounding conductors that ground the ground buss's in all the sub panels, including the isolated grounding conductors that ground the isolated ground buss's land on this main grounding buss. The ufer we install is based on 250.66, so it is quite large, up to 3/0 copper.

RePhase277

· #13 · Dec 7, 2009

David Channell said:
Out here the ufer is landed on a ground buss in the MSB and that buss is bonded to the neutral buss. So all grounding conductors that ground the ground buss's in all the sub panels, including the isolated grounding conductors that ground the isolated ground buss's land on this main grounding buss. The ufer we install is based on 250.66, so it is quite large, up to 3/0 copper.

But still... what does the ufer of its size have to do with isolated grounding?

sparky105

· #14 · Dec 7, 2009

beartard said:
Thanks for the answer. In my experience, it seems that customers ask for isolated-ground receptacles when what they want is a dedicated circuit for a piece of equipment (and mainly a pretty, orange receptacle.)

What I'm usually asked to do is run IG wire from each device to the low-voltage panel IG bar, then from there *through* the transformer to building steel and a water pipe, bypassing X0 altogether. It seems to me that such an installation could cause more trouble than good if noise is a problem.

I've even had one installation where the plans called for the Isolated GEC to go to its own driven ground rod, not bonded with the regular house system. I didn't think that was legal either, but the engineer supposedly knows what he's doing, right?

I'm an installer...one day I hope to be an electrician.

engineer is moron and will kill someone with that move the building would be one potential to ground and the IG another potential BAD BAD:blink:

sparky105

· #15 · Dec 7, 2009

David Channell said:
We are talking about separate grounding conductor back to the MSB, not the neutral. The isolated ground (ing) must be a separate conductor, insulated, and makes no contact to a grounding source except at the isolated ground buss and the main ground buss at the ufer.

that is it exactly I think in teh last 20 yrs i have seen only a hand full of true IG systems and that is exactly how it was done

the rest were just like someone else said pretty orangre rec.:thumbup:

Mastertorturer

· #16 · Dec 8, 2009

The funny thing is 99% of this isolated ground crap is not needed. All modern electronics power supplies filter and condition power. Not to mention protect for other un-desirable power conditions such as brown outs.

This is the power supply I used in the computer I built. Not the most expensive or the most advanced I might add.

http://www.enermaxusa.com/catalog/p...d=170&osCsid=19da7dc5f50bd36243ab304ec161b852

Fiddle-fart around with your bonding and grounding all you want. It won't do diddly crap compared to the power supplies being made today.

This is all just a marketing gimmick & outdated techniques to "protect" electronics. Fancy orange receptacles with triangles indeed.

Bob Badger

· #17 · Dec 8, 2009

Mastertorturer said:
The funny thing is 99% of this isolated ground crap is not needed.

I could not agree more and most times the IG gets compromised anyway so it's just a big joke and waste of money.

RIVETER

· #18 · Dec 11, 2009

lGround

InPhase277 said:
Not really. When an electrician says ground, 99% of the time they are referring to something tied to a designated electrical zero point. In the vast majority of systems, this is the neutral point. And in electronics and automotive electrical, ground is mentioned continuously, with no connection with the earth.

On this forum GROUND is in reference to earth unless otherwise stipulated.

hbiss

· #19 · Dec 11, 2009

In the old days computers and particularly point of sale systems weren't interconnected by ethernet cables. They used serial RS232 cables and unlike ethernet the RS232 cable have a ground wire that goes from each piece of equipment to the next. So if the power line grounds for each piece of equipment on the system go to different grounds in different panels (using normal receptacles) the situation exists for there to be a difference in potential between those grounds. Normally this would not cause a problem but if all the grounds on each piece of equipment were tied together through the RS232 cables then there is the liklihood for ground currents to circulate in those cables causing a data problem. Using isolated ground receptacles eliminates that problem because all their grounds are derived from a single point also.

So, like someone mentioned isolated ground receptacles are a holdover to the days of RS232. Ethernet which is used today does not carry a ground and rarely is an IG receptacle needed even if (even more rarely) it is wired correctly.

-Hal

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Old Spark

· #20 · Dec 11, 2009

At least those unnecessary orange receptacles only cost $18 to $21 each. That's a bit more than the 5362 and BR20's we use on stranded wire. I wonder why they keep specifing those 5362-I and then making sure we use them? I guess the electrical engineers are not up to date.

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