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Title: Too isolated ground
Post by: Kevin Hoober on November 22, 2013, 07:00:33 pm
I had a hunch the isolated grounding bus was not bonded to the neutral in a recent install--today I had some time and the tools needed to check it out.

After not finding any jumpers, I pulled out the meter (measuring resistance, meter reads 14.993M Ohms)(http://img.tapatalk.com/d/13/11/23/8avy9u2u.jpg)

I then got curious about the non-isolated ground:
(http://img.tapatalk.com/d/13/11/23/ry9uvyqu.jpg)

At this point, I started to question my methodology (after double checking my leads), and decided to take the cover off of the transformer...thinking surely they bonded the neutral/ground...apparently not:
(http://img.tapatalk.com/d/13/11/23/u8ega7ep.jpg)

I have seen at least one (very large) church oriented A/V/L design firm spec the iso-ground bus to not be bonded to the neutral.  Shame on the electrical contractor for complying with this unsafe practice.

This is the first time I've seen a completely unbonded neutral.

Be careful out there!

Kevin H.
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Title: Re: Too isolated ground
Post by: Mike Sokol on November 22, 2013, 07:17:37 pm
This is the first time I've seen a completely unbonded neutral.
I first saw an unbonded neutral on an iso-transformer nearly 40 years ago in a packaging plant where a 480-to-120-volt transformer was used to send relay control voltage to a dozen packaging lines in one part of the plant. When one of the hot wires was shorted out under a bolt, the Hot and Neutral bus voltages flipped, which put all the hot wires at ground voltage and all the neutral wires at 120-volts. We found this out when an electrician poked around on a neutral wire with his bare hands and got a nasty shock. That's the real danger of a floating neutral, there's no fault current from the first short which then energizes the neutral with 120-volts instead of tripping the current breaker. I make it a practice to poke a NCVT around any open box I'm in just to be sure anything that's supposed to be HOT is HOT, and everything else is NOT HOT.

Good catch...
Title: Re: Too isolated ground
Post by: Geoff Doane on November 22, 2013, 09:52:44 pm
What DID they connect the isolated ground bus to? I can't really tell from the photo.

(I know that doesn't really have anything to do with the lack of neutral bonding on the secondary of the transformer.)

The whole issue of isolated grounds doesn't seem to be be well understood by most electricians, or perhaps even theatre consultants.  I believe current code specifies that the isolated grounds have to remain in the same enclosure with the current carrying conductors (something to do with eddy currents during a fault), which seems to be violated by your picture below.  It was quite common in older installations to run the isolated grounds in their own separate conduit system for much of the run (as this seems to be).

GTD
Title: Re: Too isolated ground
Post by: Kevin Hoober on November 22, 2013, 10:43:31 pm
What DID they connect the isolated ground bus to? I can't really tell from the photo.

If you look in the bottom right corner of the first photo, you'll see the top of a (galvanized) ground rod driven thru the slab.  The wire then goes thru the bottom of the panel over to the iso-ground compartment.

Quote
The whole issue of isolated grounds doesn't seem to be be well understood by most electricians, or perhaps even theatre consultants.  I believe current code specifies that the isolated grounds have to remain in the same enclosure with the current carrying conductors (something to do with eddy currents during a fault), which seems to be violated by your picture below.  It was quite common in older installations to run the isolated grounds in their own separate conduit system for much of the run (as this seems to be).

GTD

Completely agree that the iso-ground concept (and even the purpose of the grounding conductor) is lost on many.  I had the importance of ground neutral bonding brought to my attention several years back by a knowledgable electrician during a remodel.  It took me a quite a bit of reading before I got my head around it all (mostly).

All conductors are ran in the same conduit to the branch circuits.

This is a Lyntec panel (unmodified)--I would hope the separate iso-ground enclosure is up to code.

What is also interesting is that the equipment ground on the panel appears to be tied to the #6 ground (thru the transformer frame) that was ran from the 480V panel across the building.

I now need to look through the electrical drawings from the A/V/L designer to see if they spec'd it as unbonded, or if that fell apart later.

Kevin H.

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Title: Re: Too isolated ground
Post by: Stephen Swaffer on November 25, 2013, 01:35:03 am
Code still requires isolated grounds to be bonded to the neutral.  My understanding of isolated grounds is that it is simply a dedicated grounding conductor from the sensitive equipment back to the service ground.

The unfortunate danger in this situation is that if that galvanized ground rod is any distance at all from an outside wall, it is likely in dry soil and essentially useless as a ground.  Even if it meets the 25 ohm standard for grounds, a fault to the conduit or any enclosure will most likely not trip a fault device leaving the things energized and volt/current present who knows where.

It is unfortunate, but not uncommon to find things designed by engineers that do not meet code requirements.   Maybe I expect too much from college graduates...
Title: Re: Too isolated ground
Post by: Mike Sokol on November 26, 2013, 05:56:21 pm
Even if it meets the 25 ohm standard for grounds, a fault to the conduit or any enclosure will most likely not trip a fault device leaving the things energized and volt/current present who knows where.
In actuality the 25-ohm ground standard is rarely measured. According to code, instead of measuring the actual ground impedance with something like a Fall-of-Potential test, you just have to drive a second ground rod and connect the two together. I've measured ground rod impedance over the years and find that many of them are a lot closer to 100-ohms in dry ground. See http://tinyurl.com/myvfd2x for the basics of this test. And that's why a ground rod that's not bonded to the transformer neutral isn't really a safety grounding point... it won't trip a load circuit breaker, though it will trip a GFCI. Ground rods are really there for lightning protection and to keep the voltage of your local power ground plane close to earth potential.

Mike Sokol
Title: Re: Too isolated ground
Post by: Jeff Bankston on November 27, 2013, 05:15:04 am
the iso ground is not suppose to be bonded to the neutral buss. i have done it a few different ways according to the blueprints. all the iso ground busses i installed had insulated stands and were just a neutral buss bar kit. 1. required me to run a wire to the nearest building steel. 2. required me to run to the cold water pipe at the building entrance. 3. required me to run to a seperate ground rod. 4. required me to connect to the transformer xo. i have wired many buildings that had a iso ground wire. there has ben much discussion over the years about where it gets terminated. if the plan didnt specify i would send an rfi and have the engineer tell me where to ternimate that way if equipment was affected it would fall back on the engineer and not me. i have done several add ons in buildings and have seen the iso connected to the ground buss. i have done a few remodels where the jerk off electrician stuck a short piece of green along with a short piece of green with yellow stripe wire in the conduit that went no where. yep the short piece of green is pretty common by "rip you off" electricians and the onlyt thing grounding the outlet is the conduit. the iso ground wire is suppose to be green with a yellow stripe or yellow tape. in the case of #3 and larger you use green and yellow tape on each end. NEVER trust that the ground wire is actually connected to the outlet, we have seen some b.s. work.
Title: Re: Too isolated ground
Post by: Jeff Bankston on November 27, 2013, 05:25:05 am
that trans is suppose to wired the way i have the green lines drawn. i got hit on a job once when the so called certified card carrying journeyman didnt ground the xo. yep 120v between the neutral and the ground and 198v between the neutral and the hot leg. this is how i was taught and the way they want it in california. the grfound goes straight to the xo and does not treminate to anything on the way. a seperate jumper goes between the xo and the trans case and a seperate jumper on the ground lug if your using that kind of bushing. we call the grounding type nuts ground bushings in cali.
Title: Re: Too isolated ground
Post by: Jeff Bankston on November 27, 2013, 05:26:33 am
the nut is crossthreaded !!! that iso ground wire jod is B.S. ! the ground wire should have two 1 hole straps holding it to the wall. the wire is too long and a tripping hazzard. all i see is yellow tape on the black ground wire. yellow tape is what you mark C leg on a 277/480 or C leg on a 3 wire 480 system with. when the iso ground wire is black you put GREEN and YELLOW tape on both ends. this is some more B.S. work done by idiot jerk offs that take a class to learn the answers so they can get a journeyman card but dont know SHEEET ! i fired every guy that had a journeyman card. some didnt even know what a bender or a fish tape was ! i had my bosses send the applicant to me for interviews after that. one things for sure , if you hired me to do a job it would be the best job that a human can do.
Title: Re: Too isolated ground
Post by: Jim McKeveny on November 27, 2013, 07:57:39 am
The road-dog in me wishes that the color code tape jobs were a fat 4 inches long or more. people get tired on jobsites, and line differentiation should SCREAM!

JMO
Title: Re: Too isolated ground
Post by: Frank Koenig on November 27, 2013, 11:19:24 am
the iso ground is not suppose to be bonded to the neutral buss.

250.146 (D) does not agree.  A ground fault current still has to find its way back to the grounded circuit conductor at the service entrance. "Isolated" just gives you license to run the equipment grounding conductor through as many panel boards as you want (without connection) to get to the place where you connect it to the rest of the grounding system. -F
Title: Re: Too isolated ground
Post by: John Roberts {JR} on November 27, 2013, 12:07:49 pm
Amen... the safety ground fault current must get back to the breaker panel with low enough impedance that the breakers will open under fault conditions. 

JR
Title: Re: Too isolated ground
Post by: Matthew Knischewsky on November 27, 2013, 12:49:26 pm
IMO the biggest advantage for an isolated ground in MOST audio applications is the fact that there is copper wire going from the ground rod right to the receptacle. Can't comment on other jurisdictions but here it's acceptable to use EMT conduit as the ground. Over long runs and many conduit junctions there's more resistance than wire which can cause grounding problems with our gear, especially if the conduit starts to corrode in damp environments. Similar results can be obtained by pulling a dedicated ground conductor through each conduit without doing a true isolated ground system.

And for clarity... no matter if it's an isolated ground system, ground and neutral always have to be bonded together at only one location. For most buildings that one place is the service entrance but if there's additional transformers that one place is at the XO (neutral) of the transformer.
Title: Re: Too isolated ground
Post by: Mac Kerr on November 27, 2013, 01:12:41 pm
IMO the biggest advantage for an isolated ground in MOST audio applications is the fact that there is copper wire going from the ground rod right to the receptacle.

How is this a big advantage for most audio applications?

Mac
Title: Re: Too isolated ground
Post by: Jeff Bankston on November 27, 2013, 02:29:58 pm
250.146 (D) does not agree.  A ground fault current still has to find its way back to the grounded circuit conductor at the service entrance. "Isolated" just gives you license to run the equipment grounding conductor through as many panel boards as you want (without connection) to get to the place where you connect it to the rest of the grounding system. -F
in los angeles the city electrical inspectors will not allow the iso ground to be connected to the neutral buss in a panel board. the iso ground can be connected to a transformer xo. there has ben much discussion of this over the years among electricians and electrical engineers. i am a commercial journeyman electrician.
Title: Re: Too isolated ground
Post by: John Roberts {JR} on November 27, 2013, 02:48:14 pm
in los angeles the city electrical inspectors will not allow the iso ground to be connected to the neutral buss in a panel board. the iso ground can be connected to a transformer xo. there has ben much discussion of this over the years among electricians and electrical engineers. i am a commercial journeyman electrician.

I am unclear about terminology. What is a transformer "xo"? Is that possibly the center tap on the pole distribution transformer delivering the two polarities of 120V that measure 240V across the two legs? If yes, isn't that center tap connected to neutral in the power panel?

I assume buss is same as electrical bus, not the brand of fuses.

If the isolated ground is not connected to neutral it may be ineffective as a safety ground to trip breakers. Are RCD/GFCI required for such iso-ground installations? If not they should be.

JR

Title: Re: Too isolated ground
Post by: Jeff Bankston on November 27, 2013, 03:33:10 pm
I am unclear about terminology. What is a transformer "xo"? Is that possibly the center tap on the pole distribution transformer delivering the two polarities of 120V that measure 240V across the two legs? If yes, isn't that center tap connected to neutral in the power panel?

I assume buss is same as electrical bus, not the brand of fuses.

If the isolated ground is not connected to neutral it may be ineffective as a safety ground to trip breakers. Are RCD/GFCI required for such iso-ground installations? If not they should be.

JR
there is way too much to type regarding the XO so i will post a simple reply. the xo is where you get your neutral from a transformer. the xo must be grounded. the xo in the foto has a white circle around it. i'm not trying to be a smart alec but if you really want to learn about the technical aspects of all this electrical engineering school is a must.

i have never had gfic recepticals specified for use on an iso circut. there are special recepticals that you must use. the ground hole will have a green dot next to it. the metal frame of the receptical is not connected to the ground hole.
Title: Re: Too isolated ground
Post by: TJ (Tom) Cornish on November 27, 2013, 05:08:26 pm
there is way too much to type regarding the XO so i will post a simple reply. the xo is where you get your neutral from a transformer. the xo must be grounded. the xo in the foto has a white circle around it. i'm not trying to be a smart alec but if you really want to learn about the technical aspects of all this electrical engineering school is a must.

i have never had gfic recepticals specified for use on an iso circut. there are special recepticals that you must use. the ground hole will have a green dot next to it. the metal frame of the receptical is not connected to the ground hole.
With respect, I'm pretty sure JR understands isolated grounds and bonding.
Title: Re: Too isolated ground
Post by: Frank DeWitt on November 27, 2013, 05:18:44 pm

If the isolated ground is not connected to neutral it may be ineffective as a safety ground to trip breakers. Are RCD/GFCI required for such iso-ground installations? If not they should be.

JR

A isolated ground outlet is grounded.  The ground opening in the outlet is connected to ground (isolated) and the box and cover are connected to ground (conduit / building steel)  From a safety standpoint there is no difference.  Only the path to ground is different. 

BTW it may be worth noting that GFI outlets do not need a ground to operate.  They compare the current on the hot and neutral and if they are sufficiently different, the device trips.
Title: Re: Too isolated ground
Post by: Kevin Hoober on November 27, 2013, 05:29:42 pm
the xo is where you get your neutral from a transformer. the xo must be grounded.

Looks like everyone is catching up one the board today!

One thing the install got right: there is actually green tape with the yellow on both ends of the wire going to the rod.

I was referring to XO when inappropriately using the term "neutral bus". 

Would it be common to lose the incoming ground in favor of local building steel?  This is a remodel in a warehouse (not much building steel)

My understanding is that code requires any ground (isolated or not) to be bonded to the neutral (XO). Unbonded is certainly unsafe, as others have stated, as there would not be a fault current return path.  I do not see how 3 of the 4 examples, in your first post, meet this criteria--am I missing something?

Not a journeyman electrician,
Kevin H.

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Title: Re: Too isolated ground
Post by: Jonathan Johnson on November 27, 2013, 08:01:36 pm
So what I see in the photo is a floating neutral. If iso ground must be maintained past the transformer, the neutral of the secondary (marked XO, which I assume means "crossover" for the neutral taps of the secondaries, and therefore is a neutral bus of some sort) should have a separate ground running back to the service entrance. In this case, the chassis of the transformer is grounded, so it's not really ISO ground at that point. To avoid the floating neutral it should be bonded to ground.

Is there a good reason for the floating neutral in this installation?
Title: Re: Too isolated ground
Post by: John Roberts {JR} on November 27, 2013, 09:07:28 pm
there is way too much to type regarding the XO so i will post a simple reply. the xo is where you get your neutral from a transformer. the xo must be grounded. the xo in the foto has a white circle around it. i'm not trying to be a smart alec but if you really want to learn about the technical aspects of all this electrical engineering school is a must.

i have never had gfic recepticals specified for use on an iso circut. there are special recepticals that you must use. the ground hole will have a green dot next to it. the metal frame of the receptical is not connected to the ground hole.

Thanks, I already have a pretty good handle on how the electrons behave just trying to get up to speed with the jargon..

So it is as I speculated, XO is the center-tap of the transformer. Since this gets connected to neutral with a low impedance path (I ASSume it;s low impedance), connecting the isolated ground there should be adequate to trip breakers in case of a mains fault to that ground.

I imagine there could be a subtle voltage difference between the transformer center tap and neutral at the panel, depending on balance of the two legs, and impedance of that short(?) connection path. 
 
Happy Thanksgiving folks...

JR
Title: Re: Too isolated ground
Post by: Craig Hauber on November 27, 2013, 09:22:21 pm
the nut is crossthreaded !!! that iso ground wire jod is B.S. ! the ground wire should have two 1 hole straps holding it to the wall. the wire is too long and a tripping hazzard. all i see is yellow tape on the black ground wire. yellow tape is what you mark C leg on a 277/480 or C leg on a 3 wire 480 system with. when the iso ground wire is black you put GREEN and YELLOW tape on both ends. this is some more B.S. work done by idiot jerk offs that take a class to learn the answers so they can get a journeyman card but dont know SHEEET !

I thought there was 5 yrs of apprentice before you could get a journeyman's card?  (What state allows you to get a card with just a test?)
And where's the card-carrying master on the jobsite that should be verifying everything the journeymen are doing?  (It would be like the crew chief going awol and letting the roadies set up the PA unsupervised)

Finally, if it was so wrong, you should be sending all this to whoever is in charge of the state electrical inspector that approved the end result, (along with a cc to the engineers for the job)

Quote
I fired every guy that had a journeyman card. some didnt even know what a bender or a fish tape was

I've worked with some very good electricians that do nothing but residential,  they can't remember the last time they've had to touch either of those tools either.  The fault lies more in who assigned them on that job (like sending your monitor engineer to run the video switcher)
Title: Re: Too isolated ground
Post by: Kevin Hoober on November 27, 2013, 10:11:08 pm
Is there a good reason for the floating neutral in this installation?

No, this is a typical dedicated A/V panel in an installation.  There are some odd industrial applications where the center tapped secondary is not grounded, but this ain't it!

I suspect the contractor misunderstands the concept of iso-ground.

Kevin H.

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Title: Re: Too isolated ground
Post by: Jeff Bankston on November 28, 2013, 04:16:29 am
I thought there was 5 yrs of apprentice before you could get a journeyman's card?  (What state allows you to get a card with just a test?)
And where's the card-carrying master on the jobsite that should be verifying everything the journeymen are doing?  (It would be like the crew chief going awol and letting the roadies set up the PA unsupervised)

Finally, if it was so wrong, you should be sending all this to whoever is in charge of the state electrical inspector that approved the end result, (along with a cc to the engineers for the job)

I've worked with some very good electricians that do nothing but residential,  they can't remember the last time they've had to touch either of those tools either.  The fault lies more in who assigned them on that job (like sending your monitor engineer to run the video switcher)
first of all 5 years dont mean a thing. i'v had guys on my crew that were 8 year helpers because no one has the time to train them. most companies will get one journeyman to run a crew of helpers and apprentices. thank the illegal aliens that infiltrated the construction trade and drove the bidding down. you dont need a card carrying master on the job in california. when california passed the journeyman card requirement you had to have 8600 hours of on the job experience to qualify to take the test. the hours were not checked when i took the test, they went by the honor system. all you had to do was take a weekend class that taught you the answers to the test. thats right a state approved class that cost about 200 bucks to teach you the answers. all you had to do was memorize the questions and multiple choice answers and you could pass the test. after you took the class you could take the test any time you wanted. also ,you didnt have to take the class but if you wanted to pass you needed to. there was lots of questions on the test that had(has) nothing to do with what we do in the field and some were not even about electrical. i took the class and told the teacher the whole thing was a bunch of b.s. and he agreed. anyone could fill out the online application, type in the 8600 or more hour requirement and no one ever asked to see w-2 forms or check to see that you actully worked as an electrician. then you took the class and learned the answers. then you made an apointment and on the date you went to a building and took the mulitple choice test on a computer. if you passed you paid $300.00 and got your journeyman card good for 3 years. as for reporting fraud, the system was(is) such a beauracratic nightmare that it was impossible to report fraud. also there were no questions on the test about wiring up a transformer. i came up with a 100 question and diagram test for those that "claimed" to be a journeyman or had a card. it was a fill in the blank test and i had a drawing of h1 h2 h3 x1 x2 x3 xo and the applicant had to draw the wires with a pencil and label the color code and where they terminated. i eventually stopped working for others due to this B.S.. another electrician friend did likewise. i have told friends if they need a big job done i have 2 electrical contractors that only hire competent workers. if my boss will only send me helpers when i need journeyman i can either work with what i get or quit. its the foremans job(mine) to see the job gets done right. i would always end up putting in the switch gear and terminating the connections. i couldnt train anyne because i always had a skeleton crew like everyone else. like i typed i got tired of the bs and quit. btw some years ago i worked with an electrician that was a master electrician, the guy didnt know sheeet ! just cause they got a card dont mean nothin to me.

also, residental electricians were forbidden from applying for a journeyman. it was for commercial electrical electricians only. iirc several years ago if you were just starting out in the electrical trade you had to be enrolled in an electrical school before you could work in the field.

industry definition of a journeyman electrician > an electrician that can take a set of plans and do the entire job without having to seek instruction from other electricians. this excludes rfi's that pertains to errrors or misprints on plans or extras. a foreman is a journeyman electrician that can also direct/lead/manage/supervise a crew.
Title: Re: Too isolated ground
Post by: Stephen Swaffer on November 28, 2013, 11:02:21 am
Jeff, I'll take your word for it that your electrical work is top notch-and I assume you put far more effort into your electrical classes than you did English.  I have been an industrial electrician for 16 years-much of it in the same factory.  It can be really humbling when you go back to a job you did 5 years earlier and realize that you did something that you now understand was really, really silly-been there before.  I have been a licensed master electrician and contractor for 12 years(fairly and honestly passed the Experior journeyman and master exams with 94% or better on the first try)-and I still have a lot to learn in the electrical world. (By the way master electrician=one that can draw the plans.)  I always try to find continuing ed classes that not only meet relicensing requirements but also challenge me to learn more.

I suspect that the XO-neutral-bonding question is a matter of local preference.  Iowa has only had a state program for 6 years-as yet there is very little politics on the inspection side of things and they can only enforce the NEC as written.  On a separately derived system-ie transformer supplied panel-the NEC requires the neutral to be bonded to the ground in ONE place.  This can either be the X0 bonded to the ground in the transformer-probably the most  common because it is usually the easiest-or alternatively the neutral buss can be bonded in the panel-if they are not connected in the transformer. My inspector always checks to see that one-and only one of the bonding connections is there.  The NEC does give the AHJ (authority having jurisdiction) final say-so it may be that your inspectors have decided for consistency to require bonding in the transformer and never allowing it in the panel.  There would be advantages to that from an inspection standpoint and future work standpoint when multiple inspectors and electricians are involved.  From a technical and safety standpoint the important thing is that one bonding point does in fact exist.
Title: Re: Too isolated ground
Post by: Rob Spence on November 28, 2013, 09:00:26 pm
In my state, the only difference between journeyman and master is that masters can hire employees (hence they need more business education) but have the same electrical education requirement.
So, a journeyman can be a sole proprietor and pull permits and do work but cannot have employees.
This is in my state. Your state may vary.

Sent from my iPad using Tapatalk HD
Title: Re: Too isolated ground
Post by: Samuel Rees on April 30, 2014, 07:20:36 pm
 Isn't the "safety" aspect defeated if ground isn't an alternative path to neutral? Electrical noob here... Be nice... I'm just sure I'm not the only one with this question.
Title: Re: Too isolated ground
Post by: Cailen Waddell on April 30, 2014, 08:43:27 pm

Isn't the "safety" aspect defeated if ground isn't an alternative path to neutral? Electrical noob here... Be nice... I'm just sure I'm not the only one with this question.

Yes. The purpose of a ground is to provide an alternative path for a fault current back to the neutral/ground, etc. If there is not a ground neutral bond then the breaker would most likely not trip.

I'm not an electrician, but I had to learn a lot about it to keep the electricians on the facilities we build from screwing it up.
Title: Re: Too isolated ground
Post by: Jeff Bankston on April 30, 2014, 08:55:35 pm
well let me explian this hole "master" think to ya'll. i have a masters license in baiting. i work on a boat fishing in the water.(where else would you fish ?). i started out as a junior baiter and finally pasted the master baiter test. so i am proud to say i am a master baiter.
Title: Re: Too isolated ground
Post by: Jeff Bankston on April 30, 2014, 09:13:09 pm
Jeff, I'll take your word for it that your electrical work is top notch-and I assume you put far more effort into your electrical classes than you did English.  I have been an industrial electrician for 16 years-much of it in the same factory.  It can be really humbling when you go back to a job you did 5 years earlier and realize that you did something that you now understand was really, really silly-been there before.  I have been a licensed master electrician and contractor for 12 years(fairly and honestly passed the Experior journeyman and master exams with 94% or better on the first try)-and I still have a lot to learn in the electrical world. (By the way master electrician=one that can draw the plans.)  I always try to find continuing ed classes that not only meet relicensing requirements but also challenge me to learn more.

I suspect that the XO-neutral-bonding question is a matter of local preference.  Iowa has only had a state program for 6 years-as yet there is very little politics on the inspection side of things and they can only enforce the NEC as written.  On a separately derived system-ie transformer supplied panel-the NEC requires the neutral to be bonded to the ground in ONE place.  This can either be the X0 bonded to the ground in the transformer-probably the most  common because it is usually the easiest-or alternatively the neutral buss can be bonded in the panel-if they are not connected in the transformer. My inspector always checks to see that one-and only one of the bonding connections is there.  The NEC does give the AHJ (authority having jurisdiction) final say-so it may be that your inspectors have decided for consistency to require bonding in the transformer and never allowing it in the panel.  There would be advantages to that from an inspection standpoint and future work standpoint when multiple inspectors and electricians are involved.  From a technical and safety standpoint the important thing is that one bonding point does in fact exist.
my post about terminating the ground to building steel or a nearby cooper water pipe was in reference to the I.G. ground only and not the service ground or XO ground. those have to be terminated within 5 feet of where the main water line enters the building, no exceptions allowed. back around the mid 90's there was much argumant amongst electricians and electrical engineers about where the I.G. ground was to be terminated. lots of electricians were terminating it to the common ground buss in the panel. meyself and others had ben installing a small neutral buss(because they come with plastic insulating mounts) and running a "seperate" ground wire to building steel or the xo if we could do it that way or the nearest cold water pipe. some ti's and remodels make it impossible to run a ground back to where the service ground is due to walls etc that would require us to cut holes, core floors, etc. so los angeles buildind safety allowed the I.G. to be terminated elswhere. one reson this was approved was due to service work where an office area didnt have any I.G. recepticals and it is allowed to terminate the I.G. at the restroom copper water pipe. if there is an existing I.G. buss in the panel then thats where the I.G. is terminated. on new buildings and where the I.G. ground has to be run to where the main service ground is thats what is done. If we install a transformer we have to(no exceptions) run the xo ground to the main water pipe within 5 feet of the main water pipe entrance and if walls and floors have to be cut that what is done. i probably made a mess of trying explain this but i can assure you i'm better understood in person........i think ! and my name is Ron Burgundy ?
Title: Re: Too isolated ground
Post by: Stephen Swaffer on April 30, 2014, 11:39:00 pm
Yes. The purpose of a ground is to provide an alternative path for a fault current back to the neutral/ground, etc.

The best way to accomplish this is with one bonding point for neutral/ground/and IG.  Especially since the noise the IG is installed to avoid occurs downstream from this bonding point.  That is also the best way to avoid ground loops.  That said, going to a water pipe might be workable alternative if you can't get back to the main bonding point.  By "might" I simply mean you would have to find out by trial and error if it would work-if that pipe is attached to building steel or someone else has tapped it for a ground it might not be very isolated-just depends.