This is not how you do isolated ground ....

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brantmacga said:
Hey!!! You read all of my original post !!! Thanks !!!!!


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Yeah I read the post, my problem is that I kept not looking at pic closely.:slaphead:

First I thought-no EGC, just a rod.

Then rcarrol spotted EGC and I said everything was fine-oops. Did not notice ground bars were separated.

Finally I got the big picture of the problem.
 
jumper said:
Yeah I read the post, my problem is that I kept not looking at pic closely.:slaphead:

First I thought-no EGC, just a rod.

Then rcarrol spotted EGC and I said everything was fine-oops. Did not notice ground bars were separated.

Finally I got the big picture of the problem.
Click to expand...

I just meant thanks for clarifying to everyone else telling me to do this and that!

To be fair, I do these alllll the time, so I know immediately when something is wrong.



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There are several highly respected books on grounding and bonding that do not say good things about isolated ground receptacles, even when wired to the NEC. Here is one off the top of my head:


http://electrical-engineering-portal.com/res2/Practical-guide-to-electrical-grounding.pdf


Page 70 on the paper itself:

(11) Special care must be used to assure proper
grounding if NEC permitted isolated grounding is
specified. “Isolated/Insulated grounding” (IG) must
be per NEC Section 250-74; Connecting Receptacle
Terminal to Box; exception No. 4; and Section 250-
75, Bonding Other Enclosures for field wired (e.g.,
direct) branch circuit connections to electronic
equipment.



(12) In particular, no attempt must be made during or
after installation to separate the electronic system’s
equipment grounding conductors from the ac power
system’s equipment grounding conductors and its
associated earth electrode grounding connections.
Such separations would violate the NEC and
produce potential electrical fire and shock hazards.
They would also be likely to damage circuits inside
the related electronic equipment, or to at least
degrade the operation of it.


(13) Note that the use of the IG method even if it follows
NEC requirements, does not always improve the
performance of equipment. In fact, the use of the
IG wiring method is just as likely to make things
worse or to result in no observable change to the
operation of the equipment. There is usually no way
to predict the benefits if any, of isolated ground
circuits except by direct observation and
comparison between solid grounding (SG) and IG
methods in each case.


(14) It is relatively easy to convert existing IG circuits to
SG circuits on an as-needed basis. On the other
hand, it is generally both impractical and not cost
effective to convert an existing SG circuit to an IG
style that conforms to NEC requirements.
Accordingly, circuits used to supply power to
electronic equipment can be designed and first
installed as IG types, so that they may later be
converted back and forth between IG and SG as
needed.

(15) The equipment grounding conductors in a feeder or
branch circuit must always be routed within the
same conduit or raceway containing that circuit’s
associated power circuit conductors. This also
applies to flexible cord and cable assemblies.
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The setup they have is not only a fire and electrocution hazard, but may actually damage the equipment. Any elevated voltage on the neutral will create a potential between every part and the machine's chassis. You are bringing a remote ground into the building which will always have a different voltage to the rest of the system- the last place you want that is on electronic equipment.


The correct way to do an IG is to run a second EGC originating in from the main disconnect's neutral bar, and then having that EGC isolated from the normal grounding system in every panel. An insulated IG ground bar is needed.

But- in truth what will give you a true IG is making sure there are no standing neutral to ground faults in the building. IG receptacles came about from ground loops causing interference at a time when electronic equipment would malfunction just by looking at it. The idea was that if you could bring an insulated EGC all the way back from the service disconnect you could "break" that ground loop. However, due to myths and ignorance the idea caught on that an IG was a separate express electron dump to the earth- which its not. A lot of these guys will throw words around like "common mode noise" having little to do with an IG.
 
kwired said:
The feeder EGC lands on the EGC bus bolted directly to the cabinet. The left "neutral bus" which has all the "IG" conductors landed on it, has had it's jumper to the right neutral bus removed and is insulated from the EGC and the cabinet. All that connects to it is the "IG" conductors and the ground rod.
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If you don't know how to do IG's, this could be considered a "good guess", right? :)
 
brantmacga said:
No, they're not connected at all.

The IG bar is totally isolated, and goes straight to a ground rod. There is no EGC at the devices.
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They are not connected directly but it isn't correct to say that they are not connected at all. The "isolated" ground rod has a resistive connection to every other ground rod in its vicinity. Heck, it has a resistive connection to every other ground rod on the planet.
 
petersonra said:
It appears to me that the incoming wire EGC is connected to the ground bar on the right. the conduit EGC is connected to the box. So they are bonded together back at the source.

if it makes you feel better run a wire between the two ground bars.
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The feeder EGC is connected to the regular EGC bus terminal.

To make this a correctly installed IEGC, move the feeder EGC to the IEGC bus. Regular EGC provided via feeder EMT.
 
ggunn said:
They are not connected directly but it isn't correct to say that they are not connected at all. The "isolated" ground rod has a resistive connection to every other ground rod in its vicinity. Heck, it has a resistive connection to every other ground rod on the planet.
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Seriously ?
If that's the case, I hope you don't catch my cold, since I'm breathing the same air you are.

The OP was simply sharing with us some peoples idea of an isolated ground setup who got there before he did.

Which is not as it should be.

He's going to fix it.
 
Back my my tool belt held a star-drill and a brace & bit I assisted on a job where the computer manufacturer required an install similar to the one pictured with a truly "isolated" ground (separate electrode, etc) and it passed inspection llkely because the inspector, like us. had never seen a computer before.
 
augie47 said:
Back my my tool belt held a star-drill and a brace & bit I assisted on a job where the computer manufacturer required an install similar to the one pictured with a truly "isolated" ground (separate electrode, etc) and it passed inspection llkely because the inspector, like us. had never seen a computer before.
Click to expand...

Don't feel bad.
When dad and I actually got our commador to link up with the teletype and morris code receiver we had in the back porch where you could actually read what was coming in on the screen instead of having to cipher it out we were steppin in high cotton... :)


JAP>
 
some designers want to connect IG to a building steel. When electrical designer starts a discussion with me about how to do isolated ground I ask 1 question - do you agree that all phase currents must return to originating transformer. if answer no, it's end of discussion.

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victor.cherkashi said:
some designers want to connect IG to a building steel. When electrical designer starts a discussion with me about how to do isolated ground I ask 1 question - do you agree that all phase currents must return to originating transformer. if answer no, it's end of discussion.

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But at least wth building steel your chances are much greater of having low impedance return to the source then with an isolated ground rod like OP has.
 
jap said:
Seriously ?
If that's the case, I hope you don't catch my cold, since I'm breathing the same air you are.
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If I am in the same room as you, then that could happen. We wouldn't have to come into contact.

My only quibble was with the "at all". It is relatively isolated, not absolutely isolated. There is only one ground.
 
ggunn said:
If I am in the same room as you, then that could happen. We wouldn't have to come into contact.

My only quibble was with the "at all". It is relatively isolated, not absolutely isolated. There is only one ground.
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If you are interpreting the word " isolated " as not being conducted. just stick the ground out side the panel and let it hang in free air! Then it would surely be isolated.

The confusion is in the what the installer defines as "isolated" .

If you have an isolated grounding receptacle you attach it to the isolated screw on the receptacle and don't attach it to anything all the way back to main panel ground.



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