More IG nonsense

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Andy Delle said:
Well perhaps by code but stringing isolated grounds can introduce ground loops if the gear plugged in is interconnected by other grounds such as communications cables. The principle of an isolated ground circuit is that all electrical grounds tie at a common low impedance point back at the panel thus avoiding electronic signal current loops.
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I was only referring to the Code compliant aspect. Anything beyond that is a design consideration and should be specified by construction documentation, either drawings or project spec's, or both.

You can't avoid the loops in any compliant method. 'Noise' introduced by the grounding system smay seem to meet at one point in a single point bonding premise. However, unless you go to the degree of nanometer measurement of grounding conductors between utilization equipment, that premise is faulty and provides no improvement of noise rejection by the grounding system. This is the reasoning which actually makes IG systems superfluous. The only aspect that is actually effective in an IG system is when it is run inside metal conduit. The conduit acts as an RFI shield of the wire grounding.
 
jap said:
In that case the isolated ground conductor would be permitted to be bonded to the box to establish an effective ground.

I don't see any way that a "box being bonding to a box" could ever serve that purpose.

JAP>
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If the box is electrically isolated from all other means of being [low-impedence] grounded, why not? An I-EGC is still an EGC.
 
Smart $ said:
If the box is electrically isolated from all other means of being [low-impedence] grounded, why not? An I-EGC is still an EGC.
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Yes- but one that originates from the service disconnecting means and isolated there on (and yes I know at the equipment level that isolation is usually gone).
 
mbrooke said:
Yes- but one that originates from the service disconnecting means and isolated there on (and yes I know at the equipment level that isolation is usually gone).
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There's that misconception again. An I-EGC is not required to be isolated from other EGC's all the way back to the service disconnecting means. Yes, that is how many are run... but it is not required by Code.

And nothing prohibits a metal box from being grounded by the I-EGC. If the box is electrically isolated from contact grounding, the I-EGC status is not compromised.
 
Smart $ said:
I was only referring to the Code compliant aspect. Anything beyond that is a design consideration and should be specified by construction documentation, either drawings or project spec's, or both.

You can't avoid the loops in any compliant method. 'Noise' introduced by the grounding system smay seem to meet at one point in a single point bonding premise. However, unless you go to the degree of nanometer measurement of grounding conductors between utilization equipment, that premise is faulty and provides no improvement of noise rejection by the grounding system. This is the reasoning which actually makes IG systems superfluous. The only aspect that is actually effective in an IG system is when it is run inside metal conduit. The conduit acts as an RFI shield of the wire grounding.
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I'm not a licensed EC, but an EE who designs these systems. IG does work if installed and engineered properly. The engineering encompasses the entire system, not just the electrical side. That's what i do, the whole scope. Now today with most communication systems digital, IG is not nearly as important as it was 20 years ago.

Historically one of the primary problem areas requiring IG systems was analog television plants. Even today the frame rate is 59.94hz and not locked to power line. The result in old analog systems was a hum bar that rolled through the picture - 3 phase you get three bars! Today as all broadcast television is digital signal distribution, this problem is gone.
 
JFletcher said:
Is it a code violation to use orange (IG) receptacles in place of regular ones where an IG isnt called for/needed?
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I don't see why it would be a violation as IG has nothing to do with safety. As long as the third prong is ultimately grounded and bonded to the neutral at the service the IG part makes no difference safety wise.

I have seen some hack jobs in the B class music industry studios where some house technician breaks the IG's and runs them to a dedicated ground rod. And no the ground rod is not bonded back to the service :eek:hmy:
 
Smart $ said:
There's that misconception again. An I-EGC is not required to be isolated from other EGC's all the way back to the service disconnecting means. Yes, that is how many are run... but it is not required by Code.

And nothing prohibits a metal box from being grounded by the I-EGC. If the box is electrically isolated from contact grounding, the I-EGC status is not compromised.
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Not explicitly required by code, but its the only way to get a "clean" ground that follows article 250 without driving a stray ground rod.
 
Andy Delle said:
I'm not a licensed EC, but an EE who designs these systems. IG does work if installed and engineered properly. The engineering encompasses the entire system, not just the electrical side. That's what i do, the whole scope. Now today with most communication systems digital, IG is not nearly as important as it was 20 years ago.

Historically one of the primary problem areas requiring IG systems was analog television plants. Even today the frame rate is 59.94hz and not locked to power line. The result in old analog systems was a hum bar that rolled through the picture - 3 phase you get three bars! Today as all broadcast television is digital signal distribution, this problem is gone.
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Cheaper solution would have been to eliminate standing neutral to ground faults (code violation) in the power system.
 
mbrooke said:
Not explicitly required by code, but its the only way to get a "clean" ground that follows article 250 without driving a stray ground rod.
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A design consideration, for certain. I'll not debate whether there is any merit to doing so.
 
mbrooke said:
Cheaper solution would have been to eliminate standing neutral to ground faults (code violation) in the power system.
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There is only one neutral to ground bond in any properly executed electrical system. But you do get stray voltage due to capacitance and Pi line filters used inside equipment. This way GFCI's will trip with a lot of electronic gear plugged in. With racks of gear, you can easily exceed the 5ma leakage spec due to these filters. The NEC looks the other way only because this is commercial applications and tended to be qualified personnel - or at least should be. Note too that broadcast engineers used to be licensed by the FCC and part of that licensing was electrical systems knowledge.
 
Smart $ said:
A design consideration, for certain. I'll not debate whether there is any merit to doing so.
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Note that a separate un-bonded ground rod is clear code violation. And for good reason!

Consider a lightning strike to earth. What happens between those two Earth separated ground rods?

All ground rods must be bonded by a minimum #6 IIRC.
 
Andy Delle said:
Note that a separate un-bonded ground rod is clear code violation. And for good reason!
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I was not suggesting that installing stray ground rod with no connection to the grounding system of the power source. Code does permit auxiliary rod electrodes, Some believe they provide an advantage. I do not. That is one of the design considerations I was referring to. The other was simply running an I-EGC to the local panel's regular EGC terminal bus rather than having an I-EGC terminal bus installed in the local panel and an I-EGC run back to the upstream panel, disconnect, or such. Code is quite flexible on compliant I-EGC's.
 
Smart $ said:
???

Is an isolated ground circuit?

BTW, the box can be bonded to the box here if a wood frame building and it would still technically be an isolated ground circuit.

Note it is not required that an isolated ground be isolated from regular EGC's all the way back to the service. That is another misconception about IG grounding.
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Again.
You said the box can be bonded to the box.
Didn't you mean the EGC can be bonded to the box and the receptacle bonded to the box and still be isolated since it's mounted on a nonconductive wood frame ?
Or am I loosing my mind wondering how you bond a box to a box?

Jap>
 
jap said:
Again.
You said the box can be bonded to the box.
Didn't you mean the EGC can be bonded to the box and the receptacle bonded to the box and still be isolated since it's mounted on a nonconductive wood frame ?
Or am I loosing my mind wondering how you bond a box to a box?

Jap>
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Aha! You are correct. My mind was thinking differently than what I wrote. One of those days. I just picked up on what you were laying down. :slaphead:
 
Andy Delle said:
There is only one neutral to ground bond in any properly executed electrical system.
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Was not always the case in the past- you were allowed to ground (bond) things like Clay Kilns, Ovens ect to the neutral.

But you do get stray voltage due to capacitance and Pi line filters used inside equipment. This way GFCI's will trip with a lot of electronic gear plugged in. With racks of gear, you can easily exceed the 5ma leakage spec due to these filters. The NEC looks the other way only because this is commercial applications and tended to be qualified personnel - or at least should be. Note too that broadcast engineers used to be licensed by the FCC and part of that licensing was electrical systems knowledge
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I can agree with the line filter aspect- you would be correct. But also, in many buildings standing faults contribute to or are entirely responsible for power quality problems. Even when the system is designed correctly and to the code with no such bonds per blue prints, its possible that they can inadvertently occur during construction or down the road. Id wager to say that roughly 1/2 of all buildings today in existence have at least one neutral to ground fault somewhere in the electrical system.


This is not so much to disagree with you, but rather to challenge the myths of isolated grounding by provoking insight.
 
Smart $ said:
A design consideration, for certain. I'll not debate whether there is any merit to doing so.
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I think we can both agree then :) But, you would have a voltage much closer to zero volts from the isolated ground relative to the building steal, pipes, ect then if that IG originated from a sub-panel EGC. The main ground bar is essentially the buildings voltage reference point, and assuming you have no voltage on the utility neutral it will be near zero when measured to remote earth. Think a total of 2 volts drop on the branch circuit EGC as referenced to the MBJ and a 1 volt drop on the feeder EGC as referenced to the MBJ for example.
 
mbrooke said:
I think we can both agree then :) But, you would have a voltage much closer to zero volts from the isolated ground relative to the building steal, pipes, ect then if that IG originated from a sub-panel EGC. The main ground bar is essentially the buildings voltage reference point, and assuming you have no voltage on the utility neutral it will be near zero when measured to remote earth. Think 2 volts drop on the branch circuit EGC and 1 volt drop on the feeder EGC as an example.
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IOW, where the IG remains isolated all the way back to the main or system bonding jumper, where the equipment grounding system originates, the more stable the IG reference is... but who runs the branch circuit IG all the way back to the main. It's usually just to the local panel then a feeder IG back to the main... so any 'noise' contributed by the branch equipment is 'looped' at the local level anyway.

IG amounts to an esoteric system and just how esoteric the designer wants to be. :D
 
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