# Iso grounds



## Big John (May 23, 2010)

There is no purpose to isolated grounds; they're basically snake-oil.

That said, really the only thing that makes a receptacle IG is if the ground prong isn't immediately bonded to the j-box. After that it is at the installer's discretion where they want that ground to originate.

The only requirement is that it must tie to the system bond at some point. Check your specs, often something like that is spelled out.


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## redblkblu (Mar 3, 2012)

I'd have to comb through all that for a good little while to refresh my memory. The specs on this job is a read about the length of the King James Version. I've mostly only seen it in hospitals and other medical type facilities but I haven't dealt with them in 7 or 8 years now. This one is a restaurant oddly enough.

You say they're snake oil? Why do you say that and why do they get spec'd then? Educate me.


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## Wirenuting (Sep 12, 2010)

redblkblu said:


> You say they're snake oil? Why do you say that and why do they get spec'd then? Educate me.


It's a hold over from the very early days of computers when memory was expensive and computers used a "check sum".
Back then there were no personal computers and computing was mainly used for large number crunching and a minor mistake caused a large error..

But specs are specs and it makes people feel good.. Kinda like a teddy bear and PJ's with built in feet.


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## Big John (May 23, 2010)

redblkblu said:


> ...I've mostly only seen it in hospitals and other medical type facilities...
> 
> You say they're snake oil? Why do you say that and why do they get spec'd then? Educate me.


In hospitals you're probably thinking of redundant grounding: They have an extra conductor for safety and everything is bonded together.

With IGs the thinking is by only having one ground point you stop circulating current and the interference it can create.

The reality is that any system with significant ground current was designed or wired wrong to begin with, so IGs are just a bandaid.

Further, having long-distance IGs can actually create a potential difference compared to local grounds that can cause current to flow if (when) the grounds get mixed.

Because the reality is it's difficult to keep IGs isolated once stuff starts getting plugged in. They often end up bonded to regular ground regardless.


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## don_resqcapt19 (Jul 18, 2010)

redblkblu said:


> The job I'm on right now has some circuits spec'd to be isolated ground. *Every job I've ever seen with iso grounds accomplished it by tying all the grounds from those circuits to a copper bus separate from the panels with a separate path to ground from there. *The guy who's running work on this job swears up and down he's never seen such a set up in years and years of commercial and institutional work. His idea of accomplishing this ground is installing a separate bar inside the panel and using BX with an insulated ground in addition to the normal bare ground.
> 
> Correct me if I'm missing something here but *doesn't having your normal ground and "isolated" ground bars in the same panel tub and thus bonded defeat *the entire purpose and definition of isolated?


That has never been permitted by the NEC. The isolated grounding conductor is required to run with the panel feeder circuit conductors and must be connected to the electrical system grounding at the main bonding jumper or system bonding jumper in the case of a SDS.

The grounding bus for the isolated grounds would be insulated from the panel enclosure just like the neutral bar in a sub panel.


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## Jmcstevenson (Sep 11, 2010)

Primary benefit is that it reduces or prevents the incidence of ground loops. Engineer on the last medical clinic I did went on a rant about how the system is redundant unless used with an Isolated ground panel (expensive). He said I could bond the IG's to the primary ground buss in the panel as that should still eliminate ground loops which was his concern with the radiography equipment. 

https://en.m.wikipedia.org/wiki/Isolated_ground


Sent from my iPhone using Tapatalk


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## Wirenuting (Sep 12, 2010)

Jmcstevenson said:


> Primary benefit is that it reduces or prevents the incidence of ground loops. Engineer on the last medical clinic I did went on a rant about how the system is redundant unless used with an Isolated ground panel (expensive). He said I could bond the IG's to the primary ground buss in the panel as that should still eliminate ground loops which was his concern with the radiography equipment. https://en.m.wikipedia.org/wiki/Isolated_ground Sent from my iPhone using Tapatalk


Isolated panels in hospital OR's and ICU's are a different animal. The use of them with Line Isolation monitors alert the staff to shock hazards as they happen. They are expensive but well worth the investment and maintenance and staff training.


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## redblkblu (Mar 3, 2012)

Big John said:


> In hospitals you're probably thinking of redundant grounding: They have an extra conductor for safety and everything is bonded together.
> 
> With IGs the thinking is by only having one ground point you stop circulating current and the interference it can create.
> 
> ...


That's the word I'm looking for.....redundant. Maybe then mine is more of a question of semantics. Why call it an "isolated" ground it's just additional or redundant. It's nearly impossible not to mix them.

I'm not gonna doubt you for a second about the hospitals. As I said before I have slept quite a few times since then.



don_resqcapt19 said:


> That has never been permitted by the NEC. The isolated grounding conductor is required to run with the panel feeder circuit conductors and must be connected to the electrical system grounding at the main bonding jumper or system bonding jumper in the case of a SDS.
> 
> The grounding bus for the isolated grounds would be insulated from the panel enclosure just like the neutral bar in a sub panel.





Jmcstevenson said:


> Primary benefit is that it reduces or prevents the incidence of ground loops. Engineer on the last medical clinic I did went on a rant about how the system is redundant unless used with an Isolated ground panel (expensive). He said I could bond the IG's to the primary ground buss in the panel as that should still eliminate ground loops which was his concern with the radiography equipment.
> 
> https://en.m.wikipedia.org/wiki/Isolated_ground
> 
> ...


NEC doesn't apply in Canada but I have worked some years in the states as well. The CEC basically says the same thing. Some of what I said about Big John's comment applies to yours as well.

I'm glad I made this thread. It actually made me root around in the code book a little.

10-200 Current over grounding and bonding conductors
(1) Where wiring systems, circuits, electrical equipment, arresters, cable armour, conduit, and other metal raceways are grounded, the grounding shall be arranged so that there is no objectionable passage of current over the grounding conductors.
(2) The temporary currents that are set up under accidental conditions while the grounding conductors are performing their intended protective functions shall not be considered as objectionable.
(3) Where, through the use of multiple grounds, an objectionable flow of current occurs over the grounding conductor,
(a) one or more of the grounds shall be abandoned;
(b) the location of the grounds shall be changed;
(c) the continuity of the conductor between the grounding connections shall be suitably interrupted; or
(d) other effective action shall be taken to limit the current.


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## Stretcher (May 7, 2013)

250.146(d)
2014 nec


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## Bad Electrician (May 20, 2014)

Jmcstevenson said:


> Pr*imary benefit is that it reduces or prevents the incidence of ground loops.* Engineer on the last medical clinic I did went on a rant about how the system is redundant unless used with an Isolated ground panel (expensive). He said I could bond the IG's to the primary ground buss in the panel as that should still eliminate ground loops which was his concern with the radiography equipment.
> 
> https://en.m.wikipedia.org/wiki/Isolated_ground
> 
> ...


Actually in my experience it increases problems as 90-0/0 of IG's are improperly installed per specifications.

Ground loops are a result of electricians not insuring their Neutral is clear of faults downstream from the main neutral bond connection. It is easy and inexpensive to use a megger to verify the neutrals are clear of shorts to ground and a whole lot cheaper than an IG


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## Southeast Power (Jan 18, 2009)

Bad Electrician said:


> Actually in my experience it increases problems as 90-0/0 of IG's are improperly installed per specifications.
> 
> Ground loops are a result of electricians not insuring their Neutral is clear of faults downstream from the main neutral bond connection. It is easy and inexpensive to use a megger to verify the neutrals are clear of shorts to ground and a whole lot cheaper than an IG


Then it only takes on person to wreck the whole thing.
I know what they are asking for but I dont think the designers really know what they are describing most of the time.


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## Big John (May 23, 2010)

don_resqcapt19 said:


> That has never been permitted by the NEC....


I was sure there was some sort of exception there: Those IG busbars on cherry insulators are definitely not uncommon.


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## splatz (May 23, 2015)

Computers still use checksums. I have never gotten a real solid answer on the isolated ground idea. I am hesitant to totally disregard it because the electrical engineering that went into 1970s / 1980s mainframe setups was pretty impressive. It was before my time but I remember old timers (even older timers) saying that after installing the isolated ground, it did resolve issues - even though they couldn't nail down an explanation for me. 

A lot of times on communications lines the signal reference, the equipment frame, and the shield bonded together. I can imagine that most mainframe facilities had some faults with some current on ground somewhere, all the time. That could wind up on the signal reference and into the sensitive electronics, causing commo erros at best, equipment damage at worst. 

The modern trend is different, the new standards for grounding have ground bars to bond all the equipment to in the communications wiring closets, and BIG ground wires - between wiring closets, to building steel at wiring closets, and to the interservice bridge. It's my understanding that the idea here is to keep the ground plane through the premises at the same potential and provide a low resistance path to ground for surge energy - so that taking all paths, less goes through the sensitive electronics. It makes sense, and (like the even older timers before me) I have seen facilities that install grounding along these lines and have surge problems go from weekly in the summer to not even yearly.


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## darren79 (Dec 20, 2011)

redblkblu said:


> His idea of accomplishing this ground is installing a separate bar inside the panel and using BX with an insulated ground in addition to the normal bare ground.


Exactly how I have done this on the my last few jobs. #6 insulated green from the building ground to an isolated ground bar in the panel. Then use IGBX for you branch circuits. Bare copper goes to the bond and the insulated green goes to the isolated ground bar.


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## RePhase277 (Feb 5, 2008)

If the panel is the main panel, then I can go straight to the ground or neutral bar. If it is a subpanel, then that panel should have an IG bar that is connected back to the main service.

At any rate, IGs don't go to the earth alone. That's just stupid.


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## don_resqcapt19 (Jul 18, 2010)

Big John said:


> I was sure there was some sort of exception there: Those IG busbars on cherry insulators are definitely not uncommon.


I don't know what that is


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## redblkblu (Mar 3, 2012)

Do you mean these? That's what I was referring to before.


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## Big John (May 23, 2010)

Yeah, that's what I was thinking of. Apparently by the letter of the law they actually are illegal because they are installed remotely from the phase conductors.


Makes sense, but it's a pretty common mistake.


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## redblkblu (Mar 3, 2012)

By that logic let's just do away with those pesky ground rods while we're at it.

They allow a conduit back to the panel that's put together with set screws to serve as a ground path without pulling a green into it but an additional path to ground is illegal because it isn't close enough to short directly to phase conductors? I've said before there are people who get paid lots of money to dream up things that make you sat WTF.


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## Bad Electrician (May 20, 2014)

redblkblu said:


> By that logic let's just do away with those pesky ground rods while we're at it.


OK



> *They allow a conduit back to the panel that's put together with set screws to serve as a ground path without pulling a green into it* but an additional path to ground is illegal because it isn't close enough to short directly to phase conductors? I've said before there are people who get paid lots of money to dream up things that make you say WTF.


Nothing wrong with that.


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## wildleg (Apr 12, 2009)

redblkblu said:


> Do you mean these? That's what I was referring to before.


when I see those in com rooms it is usually just for inter-system bonding and legal.


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## redblkblu (Mar 3, 2012)

Bad Electrician said:


> Nothing wrong with that.


I'm not saying anything is wrong with it just why say grounds tied to a bus with a path to earth is no good if that's allowed?


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## Roger (Jul 7, 2007)

redblkblu said:


> I'm not saying anything is wrong with it just why say grounds tied to a bus with a path to earth is no good if that's allowed?



Because at the voltages being discussed in this thread, the earth will do nothing to clear a fault, complete a circuit, protect equipment, or people.

Roger


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## Bad Electrician (May 20, 2014)

redblkblu said:


> I'm not saying anything is wrong with it just why say grounds tied to a bus with a path to earth is no good if that's allowed?


My point was they basically are no good, a connection to earth by a ground rod. Particularly in large commercial buildings to think two 8"' ground rods are going to be better than the mass of a building with concrete footers is almost laughable.


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## don_resqcapt19 (Jul 18, 2010)

Big John said:


> Yeah, that's what I was thinking of. Apparently by the letter of the law they actually are illegal because they are installed remotely from the phase conductors.
> 
> 
> Makes sense, but it's a pretty common mistake.


If they are really isolated EGCs, that is conductors that are intended to be the fault clearing path, I see that as a violation. 

The issue is the increased impedance of the remote path. On larger circuits, the increase in impedance can move you from the instantaneous trip region to the short time trip region of the OCPD trip curve. This will result in a lot more damage at the point of the fault.

Also, it looks like there is metallic conduit just before the PVC bends. If that is ferrous conduit there will be an additional increase in the impedance from the choke effect.

Now if those are just bonding conductors that are installed for reasons other than being the fault clearing path, you can install them however you want to...they are not covered by the code rules.


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## don_resqcapt19 (Jul 18, 2010)

redblkblu said:


> By that logic let's just do away with those pesky ground rods while we're at it.
> 
> They allow a conduit back to the panel that's put together with set screws to serve as a ground path without pulling a green into it but *an additional path to ground is illegal because it isn't close enough to short directly to phase conductors*? I've said before there are people who get paid lots of money to dream up things that make you sat WTF.


It has nothing to be with being close enough so there can be a physical short to the ungrounded conductors...it is simply an impedance issue.


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## redblkblu (Mar 3, 2012)

Big John said:


> Yeah, that's what I was thinking of. Apparently by the letter of the law they actually are illegal because they are installed remotely from the phase conductors.
> 
> 
> Makes sense, but it's a pretty common mistake.


....:whistling2:


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