isolated ground

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j rae

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For an isolated ground recptical can I ground it in a sub panel if there is a grounding conductor on the ground bar going back to the main???
 
DAWGS said:
Needs to run all the way back to main service.
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No it does not, there is no code requirement to do that. It is a design issue, code could careless where the IG originates so long as it is the path between the service and the recept.
 
Isolated only needs to go to point they are paying for.Cubicles often have 6 or more isolated outlets that are only isolated at best from other outlets in building but not from each other.Waste of money.
 
An IG Question

An IG Question

Using MC cable consisting of (4) 350MCM and (1) #1/0 bare ground. It has been determined that the panel being fed by this feeder has an isolated ground bar. Hence - I need a separate - insulated - ground wire to run with the feeder. Question is can I run a separate insulated ground wire strapped to the outside of the MC cable? The main problem I see is that the separate IG ground would not enter the gear in the same MC connector and also may be a code violation. Just wondering if anyone has run into this problem.
Madiuch
 
madiuch said:
Using MC cable consisting of (4) 350MCM and (1) #1/0 bare ground. It has been determined that the panel being fed by this feeder has an isolated ground bar. Hence - I need a separate - insulated - ground wire to run with the feeder. Question is can I run a separate insulated ground wire strapped to the outside of the MC cable? The main problem I see is that the separate IG ground would not enter the gear in the same MC connector and also may be a code violation. Just wondering if anyone has run into this problem.
Madiuch
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You cannot have an IG system with the cable you've described. Strapping an EGC to the outside is not an option.
 
The whole idea of IG is that (1) We are allowed (not required, but allowed) to have a receptacle for which the ground point (i.e., place where round pin is inserted) is not connected, internally to the receptacle, to the external metal parts of the receptacle, and (2) We are allowed (not required, but allowed) to run the EGC connection from that receptacle all the way back to the service panel, without connecting it anywhere along the line to any other EGC. The code does not tell us that if a panel has a separate IG bus, we must use it. It is, as has already been mentioned, a design choice.
 
I argued this point with Mike Holt at the code changes seminar last fall.
He maintains that the words in bold below require that you run the isolated grounding conductor back to the point where the system or main bonding jumper is installed. I am not sure if I can stretch that back that far, but it does require, at a minimum, that the isolated grounding conductor be run to the panel where the branch circuit originates.
250.146(D) Isolated Receptacles Where required for the reduction of electrical noise (electromagnetic interference) on the grounding circuit, a receptacle in which the grounding terminal is purposely insulated from the receptacle mounting means shall be permitted. The receptacle grounding terminal shall be grounded by an insulated equipment grounding conductor run with the circuit conductors. This grounding conductor shall be permitted to pass through one or more panelboards without connection to the panelboard grounding terminal as permitted in 408.40, Exception, so as to terminate within the same building or structure directly at an equipment grounding conductor terminal of the applicable derived system or service.
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don_resqcapt19 said:
I argued this point with Mike Holt at the code changes seminar last fall.
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I would argue that point with him, if given a chance. The words in bold require the IG wire to be run with the circuit conductors, but they do not say how far back it has to go. If you run together the IG, the ungrounded, the grounded, and the ?normal EGC? (i.e., that gets connected to the metal box and the external metal parts of the receptacle), and you run them back to the branch panel, and if you connect both the IG and the ?normal EGC? to the ground bar, you have not violated anything in the article you quoted.
 
Isolated Ground - More Info

Isolated Ground - More Info

I agree with you that MC cable cannot be used alone for an IG system because it has only one ground wire and it is bare. However, consider the arrangement at hand which describes in detail how the IG will be made:
A 150Kva 208 delta primay to 120/208Y 3ph 4w secondary transformer will be being fed 3 phase 208V from a switchboard with (3) phase conductors and a ground. OK. The transformer will be equipped with an Isolated Ground Bar in addition to the normal grounding stud. The IG bar and the grounding stud in the transformer will be bonded together and to the Neutral XO terminal. A feeder from the secondary of the transformer will consist of (3) phase conductors, (2) neutrals and one EGC - all in one steel conduit. The feeder will be run to a 120/208V panelboard - call it Main Panel "MP". "MP" in turn will have the MC feeders that will run to downstream panels equipped with IG ground bars. Call the downstream panels "DP1", "DP2", etc. The engineer has required that IG conductors originate at the IG bar in the transformer and be run to the DP's (OK to pass through MP) and terminate on the IG bar in the DP's. So - without the IG bars or IG conductors, the whole system is normal wiring and meets code. Agree so far? Then in addition to the normal EGC which is bare Al run in the jacket with phases and neutral, there will be an additional, insulated, green/yellow striped IG conductor running outside the MC cable that will originate in the transformer at the IG bar and terminate at the IG bar of the DP's while touching nothing in between. The EGC that will run with the feeder from MP to the DP's will terminate at the normal ground bar in the DP's but will not connect to the IG bar in the DP's.
The engineer wants the branch circuits that will be taken from the DP's to have an IG that originates at the separately derived source (the 150Kva transformer) and touch nothing until it is terminated at the loads being fed from the DP's. The EGC from the DP's will still terminate to any steel enclosure at the load end but the ground terminal for the load will receive the IG and nothing else. Same arrangement as in an IG receptacle. Comments?
 
madiuch said:
Comments?
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Yes, in general when people make long posts with few spaces they tend to be hard to read and are to a large extent ignored.

In is my suggestion you try to be more concise and put some breaks in your post.
 
Back to the question.

What you describe could provide the IG, however you can not do it as it violates the NEC, 300.3(B) and 250.34(B)

You can not run an equipment grounding conductor IG or not, along the outside of the MC cable.
 
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thanks bob I do that all the time sorry I will try and be more considerate..

You are still saying though you need to run a seperate conductor exclusive of the main cable assemblies..Am I reading that correctly..
 
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Isolated Ground - More Info #2

Isolated Ground - More Info #2

I apologize for the long post - I tend to overexplain.

Yes - I guess what I am asking is if the IG can run external to the normal feeder. It would be the same as adding an IG to an existing feeder with no terminations between the transformer where the IG originates and the IG bar that would be added to the panel it serves.
 
madiuch,
The isolated equipment grounding conductor is still an EGC and 300.3(B) applies. It must be in the same raceway or cable as the circuit conductors.
 
don_resqcapt19 said:
I argued this point with Mike Holt at the code changes seminar last fall.
He maintains that the words in bold below require that you run the isolated grounding conductor back to the point where the system or main bonding jumper is installed. I am not sure if I can stretch that back that far, but it does require, at a minimum, that the isolated grounding conductor be run to the panel where the branch circuit originates.
Click to expand...

A section in need of revision.

The words in bold do not specify which circuit conductors. Are they Branch Circuit conductors or Feeder Circuit Conductors or both?

My problem with this section has always been these words:

......so as to terminate within the same building or structure directly at an equipment grounding conductor terminal of the applicable derived system or service.

The operative words above are".....so as to terminate....."
I take this to mean: Do what you have to in order to accomplish what follows. What follows is where they terminate.

There are two possible scenarios. One you have a step down xfmr and two you have a single voltage building.

Under scenario one, you can land it anywhere you want up to and including the xfmr. Key words in the Code are:
"...an equipment grounding conductor terminal of the applicable derived system...."
The definition of SDS includes premises wiring. That would lead me to say anywhere in the premises wiring system.

Under scenario two the building is served by a voltage that is not transformed. Here the key words are:
"...an equipment grounding conductor terminal of the applicable ...... service."
The definition of service limits us to the "The conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served."
That would lead me to say the Isolated Equipment Ground must terminate inside the Service Equipment.

Learned interpretations here on this forum as well as a CMP member Michael Johnston have all stated that you can terminate the Isolated Equipment Ground at any panel between the receptacle up to and including the xfmr or service.

I am of the same opinion. I do not insist the Isolated Equipment Ground go all the way back. I still get electricians and designers who want to take it to a ground rod or building steel.
 
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