Isolated Ground Termination Point

[infinity]

Discussing an IG system with another electrician and discussing where to run the IG from the isolated ground bar in the panel. IMO it should go back to the X0 of the transformer or the point where the MBJ is located in the service. One common method to run it to the closest building steel which I questioned as to whether or not it's code complaint. Any code reference that prohibit using the building steel? We typically follow this graphic:

 

[dkidd]

From https://iaeimagazine.org/magazine/2...-circuits-got-clean-grounds-or-dirty-grounds/



Installing Isolated Grounding Circuits

For a truly clean isolated (insulated) equipment grounding conductor, the insulated equipment
grounding conductor must remain insulated all the way to the point of grounding at the applicable
service or separately derived system. Does it have to, in order to meet the provisions of Section
250.146(D)? The answer is no. Section 250.146(D) is permissive text which allows the insulated
equipment grounding conductor to pass through one or more panelboards or other enclosures without
a grounding connection so as to terminate at the grounding point at the service or separately derived
system. Similar provisions are located in Section 408.40 Exception.
Obviously it is better from a design standpoint to keep this isolated (insulated) equipment grounding
conductor all the way back to the source or service, but in meeting the minimum requirements of the
NEC, it is not necessary to connect at that point, but it definitely is required to be connected to the
equipment grounding conductor of the system at some point to meet the requirements of 250.4(A)(5).

 

[dkidd]

Note that 250.146 (D) prohibits the isolated ground from leaving the building or structure, so if the transformer is outside, you could not go to the XO terminal.

 

[don_resqcapt19]

The isolated grounding conductor is an EGC and there is no provision that lets you use the building steel as an EGC. In my opinion it should go to the location of the system bonding jumper if the circuit is supplied by a transformer or to the location of the main bonding jumper if the circuit is supplied from the service.

 

[Jamesco]

250.146(D) states the insulated isolated equipment grounding conductor shall connect to the equipment ground bar in the panel the circuit conductors are fed from, OR, it can pass through one or more panels without a connection to the panel equipment ground bar as permitted by 408.40 Exception. The Exception of 408.40 allows the isolated grounding conductor to connect to the equipment ground of the applicable derived system or service with in the same building or structure.

NEC says nothing about connecting the IG insulated conductor directly to any grounding electrode, building steel. Not to mention it would defeat the purpose of the IG wouldn't it?

 

[petersonra]

Discussing an IG system with another electrician and discussing where to run the IG from the isolated ground bar in the panel. IMO it should go back to the X0 of the transformer or the point where the MBJ is located in the service. One common method to run it to the closest building steel which I questioned as to whether or not it's code complaint. Any code reference that prohibit using the building steel? We typically follow this graphic:

View attachment 20210

IMO you can run it to any ground bar you want back to and including the service point as long as it goes with the circuit conductors at least as far back as where they originate.

You can also connect a grounding electrode to any ground bar you want.

Since it doesn't do any good anyway what difference does it make?

I would point out that if you choose to run it a long way, it might no longer be an effective ground fault path so you might want to consider if you have to increase its size.

 

[infinity]

I agree that the concept of an IG system is obsolete but some people are still installing them. I remember years ago it was common to just run a #6 to the nearest steel beam and connecting it to the IG bus in the panel. On one job some actually installed this for the IG. It's an oldie but a goodie.

 

[dkidd]

There's no bonding bushing on the raceway.

 

[GoldDigger]

There's no bonding bushing on the raceway.

That's not a raceway, it's a sleeve.


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