isolated grounds

[jzombek6]

would like to know the approved method of the nec on where the iso ground is terminated. local inspector say branch circuit iso grounds must go back to main service ground at the mdp. drawing show a#6awg from branch panel to main service ground at the mdp. in branch panel the the ground bar is isolated from equip ground with standoffs. everyone i have talked to have never heard of taking branch iso ground back to mdp.
also,can you give code reference so i can look up.
thank you for your time
jzombek6

 

[Dennis Alwon]

In general the isolated ground is meant to be brought back to the main service however I don't know that the NEC has anything to say about this.

 

[texie]

I think the inspector is mistaken. This is a design issue, not an NEC issue. But from what you are saying, you have an isolated ground back to the service anyway. Also I'm assuming that you also have the regular ground for the strap, box and conduit.

 

[jzombek6]

YES,THERE ARE TWO GROUNDS IN CONDUIT-EQIUP AND ISO GROUND. IF THIS A DESIGN ISSUE,SHOUDN'T IT CONFORM TO THE NEC. PLEASE EXPLAIN FURTHER IF POSSIBLE

 

[texie]

YES,THERE ARE TWO GROUNDS IN CONDUIT-EQIUP AND ISO GROUND. IF THIS A DESIGN ISSUE,SHOUDN'T IT CONFORM TO THE NEC. PLEASE EXPLAIN FURTHER IF POSSIBLE

Take a look at 250.146(D) and 408.40 Exception. Note the language says "may" not "must". Besides, from your description you have acheived the same result with the isolated ground bar in the sub panel that does go back to the service. Many of these are done with the isolated ground terminating at the sub panel-not the service. (i'm not saying I endorse this, but it is compliant.)

 

[infinity]

I think the inspector is mistaken. This is a design issue, not an NEC issue. But from what you are saying, you have an isolated ground back to the service anyway. Also I'm assuming that you also have the regular ground for the strap, box and conduit.

I agree, although one system may be better than another you're not required by the NEC to use the better one. IMO you could install an IG receptacle and ground it to a metal box if you wanted.

 

[Smart $]

YES,THERE ARE TWO GROUNDS IN CONDUIT-EQIUP AND ISO GROUND. IF THIS A DESIGN ISSUE,SHOUDN'T IT CONFORM TO THE NEC. PLEASE EXPLAIN FURTHER IF POSSIBLE

The first thing to understand about isolated grounding conductors is that they are technically isolated equipment grounding conductors (I-EGC). The only difference under the NEC is that I-EGC's are permitted (i.e. not reqiuired) to pass through boxes/enclosures/raceways/etc. without bonding to the metallic non-current-carrying parts. This is why you must run a 'regular' EGC, too, when there are metallic non-current-carrying parts that are required to be bonded. The source/line end of an I-EGC must terminate to the EGC system somewhere... but the NEC does not specify where.

BTW, QUIT YELLING AT US!!! We can hear just fine.

 

[Bill Annett]

HI. I am the inspector that jzombek6 is speaking of. I told Joe about this site, I really tell a lot of electricians about this site because it is a great site to gain information. I guess that article 250.146 (9D) does not state that it has to go all the way to the service disconnect. I copied and pasted the article below.

D) Isolated Receptacles. Where installed 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 connected to an insulated equipment grounding
conductor run with the circuit conductors. This equipment
grounding conductor shall be permitted to pass through one
or more panelboards without a connection to the panelboard
grounding terminal bar 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. Where
installed in accordance with the provisions of this section,
this equipment grounding conductor shall also be permitted
to pass through boxes, wireways, or other enclosures without
being connected to such enclosures.

( Thanks Again Jumper for the item you gave me, as you can see it can in handy )

I was going off of a Soars Grounding and Bonding book. This book shows both ways. The NEC says just to ? an Equipment grounding conductor terminal ? it does not say it has to go to the Service disconnect location. I corrected my mistake and said that it was installed as per design. The install is ok he did not have to change anything.

Thanks to everyone who posted.


Bill Annett

 

[texie]

HI. I am the inspector that jzombek6 is speaking of. I told Joe about this site, I really tell a lot of electricians about this site because it is a great site to gain information. I guess that article 250.146 (9D) does not state that it has to go all the way to the service disconnect. I copied and pasted the article below.

D) Isolated Receptacles. Where installed 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 connected to an insulated equipment grounding
conductor run with the circuit conductors. This equipment
grounding conductor shall be permitted to pass through one
or more panelboards without a connection to the panelboard
grounding terminal bar 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. Where
installed in accordance with the provisions of this section,
this equipment grounding conductor shall also be permitted
to pass through boxes, wireways, or other enclosures without
being connected to such enclosures.

( Thanks Again Jumper for the item you gave me, as you can see it can in handy )

I was going off of a Soars Grounding and Bonding book. This book shows both ways. The NEC says just to “ an Equipment grounding conductor terminal “ it does not say it has to go to the Service disconnect location. I corrected my mistake and said that it was installed as per design. The install is ok he did not have to change anything.

Thanks to everyone who posted.


Bill Annett

Wow, I'm impressed! First of all, we don't often hear of the end of the story for most posts. Second, how refreshing to have the actual inspector involved contributing to the discussion and coming to a different conclusion based on new information. Wish we could have more of this.
On a side note, based on the way I understand the OP, it seems that the isolated ground went back to the service anyway in an isolated fashion, just not as one contiguous conductor (through the isolated ground bar in the sub panel).