Isolated ground

[don_resqcapt19]

inspector23,

" 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 the equipment grounding conductor terminal of the applicable derived system or service."

I choose to look at the words in red. There is no requirement to do anything other than provide an EGC connection to the isolated grounding receptacle. Everything past the words "shall be permitted" is optional not required. That takes the words "directly at the..." out of play.
Don

 

[inspector23]

inspector23,

[/i][/u]I choose to look at the words in red. There is no requirement to do anything other than provide an EGC connection to the isolated grounding receptacle. Everything past the words "shall be permitted" is optional not required. That takes the words "directly at the..." out of play.
Don

That's pretty interesting.

We interpret the words in red to mean that it is OK to pass through one or more panelboards without connection to the panelboards on their way to the termination point of the system. In other words, "shall be permitted" applies only to the routing of the IG. They are still required to terminate at the service, in our interpretation.

I would not understand the requirement for an IG if you could just terminate anywhere.

Could you please explain the reason for the section 250.146 (D) in the NEC if you can terminate anywhere?
Thanks!:smile:

 

[Jim W in Tampa]

inspector23,

[/I][/U]I choose to look at the words in red. There is no requirement to do anything other than provide an EGC connection to the isolated grounding receptacle. Everything past the words "shall be permitted" is optional not required. That takes the words "directly at the..." out of play.
Don

I just went thru this with an inspector a few months ago and he demanded i not hook up that IG on a power pole without actually having it.I somewhat must agree with him.If customer understood (they dont)then they think something thats not really true,but then how can a power pole offer such a fake promise

 

[iwire]

I would not understand the requirement for an IG if you could just terminate anywhere.

But there is no NEC Requirement for an IG.

Could you please explain the reason for the section 250.146 (D) in the NEC if you can terminate anywhere?
Thanks!:smile:

Sure I can give you my opinion.

If 250.146(D) did not exist it would be imposable to install any IGs as without (D) you would be in violation of the general requirement of 260.146.

250.146 Connecting Receptacle Grounding Terminal to Box.

An equipment bonding jumper shall be used to connect the grounding terminal of a grounding-type receptacle to a grounded box unless grounded as in 250.146(A) through (D)

So that first section tells us we are required to bond the receptacle to the box.

Then 250.146(D) gives us permission not to bond it to that box.

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 408.20, 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.

90.5(B) Permissive Rules. Permissive rules of this Code are those that identify actions that are allowed but not required, are normally used to describe options or alternative methods, and are characterized by the use of the terms shall be permitted or shall not be required.

 

[don_resqcapt19]

inspector,

In other words, "shall be permitted" applies only to the routing of the IG. They are still required to terminate at the service, in our interpretation.

That is exactly how I am applying the working...the route can be to any point where there is an EGC.

I would not understand the requirement for an IG if you could just terminate anywhere.

That requirement is not a code rule. The only code rule says that you must have an EGC to the IG outlet. Now, if the specs called for an IG outlet, then you have to work that out with the owner and or engineer. In any case, there is no evidence that an IG outlet has any advantages over a standard outlet.
Don

 

[don_resqcapt19]

Jim,

I somewhat must agree with him.If customer understood (they dont)then they think something thats not really true,but then how can a power pole offer such a fake promise

I don't believe this is a code issue. The only code issue is to provide an EGC to the U ground at the IG receptacle.
Don

 

[Jim W in Tampa]

Jim,

I don't believe this is a code issue. The only code issue is to provide an EGC to the U ground at the IG receptacle.
Don

If customer sees that triangle and knows what it means then he/she exspects it be one and not a fake.Ialso pointed out to the installers that its a bad idea to make all the computers end up on same circuit.All i can do is hope.There guy this morning seemed to understand and said he will have them swap them out and put only 2 on a phase.

 

[iwire]

If customer sees that triangle and knows what it means then he/she exspects it be one and not a fake.

Jim what is a fake IG?

Where did you find a description of what a 'real' IG is?

To me a fake IG would be a receptacle connected to an isolated ground rod.

 

[infinity]

What is a real IG? I've seen engineers come up with all different configurations for an IG system (XO, building steel, service). I agree with Don, to satisfy the NEC all you need to do is provide an EGC to the device. Anything beyond that is a design issue.

 

[Jim W in Tampa]

Jim what is a fake IG?

Where did you find a description of what a 'real' IG is?

To me a fake IG would be a receptacle connected to an isolated ground rod.

To me it means a ground that is not shared till it reaches the mdp.Otherwise why not just put them in place of every receptacle.To be an IG on a power pole to 6 cubicles is a real laugh.Your isolated from everything sept the other 5 cubicles.Just what value is that.

 

[iwire]

To me it means a ground that is not shared till it reaches the mdp.

Jim, Thats fine, that is your idea of an IG and it matches some engineers idea.

Others would say that what you do is not an IG either.

Do you run a seperate conecuctor from each receptacle back to the 'MDP' or do you join them along the way?

 

[Brady Electric]

Isolated ground

First of all I agree with everything I-Wire is saying about this subject,("we didn't just fall off the turnip truck"}'
So here's how I got there.
From the transformer a three wire to meter base, meter base to main panel three wire, all grounds and neutrals under the same bar. Then if you have a sub panel and only then you separate the ground and neutral. Then the ground is isolated. Many years ago we put in allot of isolated ground outlets but now most people use the surge protected bar's. If anyone can ever explain how the ground is isolated from the transformer down the line I will listen but as far as I know no mater what you do the ground will not be isolated from the neutral and will touch somewhere down the line. All I can understand about this is that by being isolated in a sub-panel and using an isolated grounding outlet makes the isolation of the ground in the outlet closer to a fault than in the main panel.
After all I'm just an old salty electrician trying to do good work and understand anything new I can.
What really gets to me is that most people say I do it because I'm told to do so and have no idea why.
That's my 3 cents worth
Semper Fi.

 

[dereckbc]

If anyone can ever explain how the ground is isolated from the transformer down the line I will listen but as far as I know no mater what you do the ground will not be isolated from the neutral and will touch somewhere down the line.

I will take a crack at it.

The IG form of grounding is only intended to be used as a POSSIBLE means of obtaining common-mode electrical-noise reduction on the circuit in which it is used. It has no other purpose and the effects are unpredictable, and likely to make the problem worse. IGR are passive circuits and cannot remove any common-mode noise period, junk in-junk out.

This is where a transformer comes into play. A transformer is one the best means of removing common-mode noise from any circuit, and forms a new ground reference point free of any noise. A plain ole every day dry-type transformer provides a minimum of 40 decibels of common-mode noise reduction. A special purpose isolation transformer can provide up to 160 db of CMR.

 

[Brady Electric]

Isolated ground

Thanks for you input. I try to do good work and do it according to the NEC always.
But there a lot of things we do because the NEC says to and the codes favorite words are shall, shall not so we do it sometimes not understanding it fully.
Most people don't admit they don't know why or how something works, they just don't won't controversy. Just a they are just a few of us they go by our bussiness name on the form. You never know is reading what you say so I just us honesty in my opinions.
I really appreciate the form and the ones that choose to participate. Semper Fi.