iso ground circuits?

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mgmelec

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Heres an electric 101 question. What is the proper way to install an isolated ground circuit? Starting point being main breaker load cener, using romex to iso ground receptical. I ran 12-3 w/ grnd. using red wire to device yolk, bare wire to metal box. At panel both red and bare to grnd. bar. Is this ok?
 
mgmelec said:
Heres an electric 101 question. What is the proper way to install an isolated ground circuit? Starting point being main breaker load cener, using romex to iso ground receptical. I ran 12-3 w/ grnd. using red wire to device yolk, bare wire to metal box. At panel both red and bare to grnd. bar. Is this ok?
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No, you cannot re-identify the red conductor as an IG conductor. You would need to use a 12/2 type AC-HCFC, where the outer jacket would ground the box and the green EGC would ground the IG receptacle.

Why are you using an IG setup in the first place?
 
chicar said:
Make sure you recolor the red wire to green with yellow stripe. Everything else you said sounds good.
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What article permits you to re-identify the red #12 as an EGC?
 
If you are using a plastic box you will only need 12/2 NM, the EGC is already isolated in this case.

Roger
 
For a true isolated ground configuration you need to mount an insulated ground bar in the panel and run a seperate ground wire back to the water main.

In the past I have used 12/3 MC cable for isolated grounds. I strip the red wire bare at both ends at the box & panel, use that for the EGC & use the insulated green wire for the isolated GND wire. So far the AHJ in my area doesn't have a problem with doing that
 
My supply house stocks "isolated ground MC", that has one green and one olive conductor. The trick is remembering which one to use for the box and which one to use on the device. Hard to tell them apart in low lighting situations. The HCFC (green armor) seems like a better idea. Not sure how the difference would cost out.

roger said:
If you are using a plastic box you will only need 12/2 NM, the EGC is already isolated in this case.
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Uh-huh. Sometimes, you can overcomplicate the situation.
 
Bob Kraemer said:
For a true isolated ground configuration you need to mount an insulated ground bar in the panel and run a seperate ground wire back to the water main.

In the past I have used 12/3 MC cable for isolated grounds. I strip the red wire bare at both ends at the box & panel, use that for the EGC & use the insulated green wire for the isolated GND wire. So far the AHJ in my area doesn't have a problem with doing that
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Bob, are you saying you expect the water main to act as a Fault clearing path, or the GEC connected to it as an EGC back to the grounded conductor?

Roger
 
mdshunk said:
Uh-huh. Sometimes, you can overcomplicate the situation.
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Marc, certainly that didn't confuse you? ;)

Roger
 
roger said:
Marc, certainly that didn't confuse you?
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Nope, I was agreeing with you. Sometimes you can overthink stuff. If the jacket or raceway is nonmetallic, and the boxes are nonmetallic, you only need one ground path for IG circuits... and it's already isolated. When IG is talked about, the tendancy is to automatically switch into "two ground paths" mode.
 
Bob Kraemer said:
For a true isolated ground configuration you need to mount an insulated ground bar in the panel and run a seperate ground wire back to the water main.
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No good. If the power source is the service, the iso gnd connects to the gnd bar where the bonding jumper is installed.

If the power source is a downstream xfmr (separately derived system) then the iso gnd starts at the transformer neutral to gnd bond. The N-G bond could be at the first disconnect or panel on the secondary but locating it at the xfmr is preferred.

In either case, from the bonding point downstream to the recept the iso gnd conductor is isolated from equipment grounds in any panel along the way.
 
Bob Kraemer said:
For a true isolated ground configuration you need to mount an insulated ground bar in the panel and run a seperate ground wire back to the water main.
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Incorrect and not compliant. In fact it would cause more common mode problems (noise). A so called true IGR originates at the N-G bond of the service or SDS, just like its EGC counterpart.

FWIW if this is a stick-built house using plastic boxes and Nm cable, every circuit is already an IGR circuit just by the nature of the construction and materials used.
 
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Bob Kraemer said:
For a true isolated ground configuration you need to mount an insulated ground bar in the panel and run a seperate ground wire back to the water main.
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I believe that merely landing on the same bus as the GEC's is adequate.

In the past I have used 12/3 MC cable for isolated grounds. I strip the red wire bare at both ends at the box & panel, use that for the EGC & use the insulated green wire for the isolated GND wire. So far the AHJ in my area doesn't have a problem with doing that
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Same here, and same results.
 
roger said:
If you are using a plastic box you will only need 12/2 NM, the EGC is already isolated in this case.

Roger
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With this setup you cannot use an IG receptacle since it will not ground a metal plate. The yoke on the device is not connected to the EGC so it is not grounded. This option will work unless someone is specifying an IG receptacle.
 
infinity said:
With this setup you cannot use an IG receptacle since it will not ground a metal plate. The yoke on the device is not connected to the EGC so it is not grounded. This option will work unless someone is specifying an IG receptacle.
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Or plastic plates.

I thought about that after I had posted and didn't want to go back to edit it.

Roger
 
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