iso ground circuits?

[chevyx92]

I know of the violations but I can't count how many times I've seen 12/3 mc ran for an isolated ground circuit and they have used the red wire to yoke(without even attempting to reidentify the red wire).

 

[haskindm]

I can't count the number of sub-panels that I have seen with the grounds and neutrals connected together. The fact that it is common practice, does not make it code compliant or OK. I believe that the main advantage of installing an IG circuit is that it allows you to take the IG ground through the sub-panel(s) and back to the ground/neutarl bar in the main service, thus by-passing any incorrectly installed sub-panels with neutral/ground connections. If there are no sub-panels, or they are installed correctly there is little or no benefit from an IG receptacle. An IG circuit is NOT allowed to have the grounding conductor run to an isolated grounding electrode. This will create a very dangerous situatin with no way to clear a ground fault.

 

[LarryFine]

I believe that the main advantage of installing an IG circuit is that it allows you to take the IG ground through the sub-panel(s) and back to the ground/neutarl bar in the main service, thus by-passing any incorrectly installed sub-panels with neutral/ground connections.

If I'm not mistaken it's more so that any currents (that should not exist) on the system EGC/conduits will not bring electrical noise into the electronics that depend on the EGC to take any such noise out of the equipment.

An IG circuit is NOT allowed to have the grounding conductor run to an isolated grounding electrode. This will create a very dangerous situatin with no way to clear a ground fault.

This is very true. Remember that the isolated grounding conductor is still the only EGC available to the plugged-in equipment, and must return to the system neutral at the bonding point to clear faults.

Earlier, when I mentioned that the isolated grounding conductor should land where the GEC's do, I was hinting that this is the point where the system neutral is bonded to the EGC's and the GEC's.

 

[haskindm]

That is what I am tring to say. In a properly installed and maintained electrical system there is no current (noise) flowing on the grounding conductor so no advantage to an isolated ground receptacle. IG is a bandaid that was invented to "fix" improperly installed systems, or at least "mask" the symptoms.

 

[mgmelec]

never did i think this thread would cause so much controversy. to clear things up a little more, the installation is at a friends stick built home, device is for computer , ups, and associated equipment. friend read somewhere that isolated, insulated ground recep. is whats needed for his application. i know re identifing conductors smaller than#6 is a violation, but ahj in my area will fail a job with a white hot leg such as an a/c disco. their remedy is to break out the black sharpie and re identify the white conductor. why not reidentify red cond. green in certain situations. still not sure what general conscensus is.

 

[haskindm]

If this is in a dwelling with NM cable and plastic outlets he already has an isolated ground receptacle. Install a seprate circuit for this equipment and he will have the most isolated ground that is available anywhere without the expense of running two ground wires or buying isolated ground receptacles. People that do not understand wiring should ask questions before accepting statements as fact. Without metal raceways, subpanels, metal boxes, etc that you would find on a commercial job, there is no benefit in using IG receptacles.

 

[dereckbc]

the installation is at a friends stick built home, device is for computer , ups, and associated equipment. friend read somewhere that isolated, insulated ground recep. is whats needed for his application.

Well I think by now you should know what is true and what is fiction. Since this is a stick built house, he is already has IGR assumong NM and plastic boxes were used.

If he wants a caddilac circuit, run a dedicated standard SG recept using NM and a plastic box and he is set to go with the best possible service other than a true "Dual Conversion UPS", which I gaurantee he cannot afford, and if he could, there would be no need for any special dedicated or IGR circuit since a Dual Conversion UPS is SDS. Any UPS under a $200 is nothing more than a vibrator with a battery, and doesn't really do anything. But that is another thread.

 

[Dennis Alwon]

i know re identifing conductors smaller than#6 is a violation, but ahj in my area will fail a job with a white hot leg such as an a/c disco.

This is not always true. Art. 200.7(C)(1)

Why not reidentify red cond. green in certain situations. still not sure what general conscensus is.

I believe you can 250.119 (B) but in a residence it would be hard to provide supervision that only qualified individuals would service the installation.

 

[infinity]

Trever,try 250.119

I never try to jump on the "conditions of maintenance and supervision ensure that only qualified persons service the installation" bandwagon. As it turns out in this installation the re identification of the red conductor as an EGC would be a violation since this is in a dwelling.

 

[Bob Kraemer]

My apologizes to everyone here, when I posted about a separate wire back to the water pipe from the isolated ground bar I meant to say service ground.
Don't know what I was thinking. Sorry
Yesterday was a bad day been having to many Mondays in a row.