Isolated Ground Circuit

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
I know little about the "voo-doo" of these type circuits, but enough to know that I don't believe they accomplish anything. With that said, I've been asked to bid on a job that calls for some isolated ground receptacles.

My question is can more than one isolated ground be on the same circuit?
If so, how do you run from one receptacle to the rest?
If some receptacles are in a separate room (same building) can you jump over to the other room to pick up those receptacles?

Is it common when using cable (MC or NM) to re-identify one of the ungrounded conductors for the isolated ground?
 

iwire

Moderator
Staff member
Location
Massachusetts
We would use IG MC cable, it will have a green and a green with yellow along with the circuit conductors.

I am not sure what you mean by 'jump over' the IG must run with the circuit conductors, back to the panel they originate from and ideally back to the bonding point at the service or SDS that supplies the circuit.
 

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
My question is can more than one isolated ground be on the same circuit?
If so, how do you run from one receptacle to the rest?
If some receptacles are in a separate room (same building) can you jump over to the other room to pick up those receptacles?
An IG is not one wire. Basically it's the same as a regular EGC it's just not pig tailed to any metal junction boxes or any sub-panel EGC buss bars, kinda like getting in the car pool lane on the freeway while all the other cars are stuck in that stop and go traffic.

A lot of houses have isolated grounds in them by nature of the wiring methods. If you use NM and PVC boxes for a kitchen counter top circuit you have a IG circuit.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
We would use IG MC cable, it will have a green and a green with yellow along with the circuit conductors.

I am not sure what you mean by 'jump over' the IG must run with the circuit conductors, back to the panel they originate from and ideally back to the bonding point at the service or SDS that supplies the circuit.
I meant run the cable over to another room. I know the EGC runs with the other conductors.

An IG is not one wire. Basically it's the same as a regular EGC it's just not pig tailed to any metal junction boxes or any sub-panel EGC buss bars, kinda like getting in the car pool lane on the freeway while all the other cars are stuck in that stop and go traffic.

A lot of houses have isolated grounds in them by nature of the wiring methods. If you use NM and PVC boxes for a kitchen counter top circuit you have a IG circuit.
I understand what an IG is I just didn't know if you can have multiple receptacles on one circuit and if that circuit could be in more than one room.
 

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
I meant run the cable over to another room. I know the EGC runs with the other conductors.
Yes you can do that.

I understand what an IG is I just didn't know if you can have multiple receptacles on one circuit and if that circuit could be in more than one room.
Yes you can do that.

Probably the easiest way is to use that special mc that iwire mentioned, it has two greens in it. I have used 12-3 mc, stripped the red insulation off at the connector for the regular egc and used the green for the isolated ground in a pinch.
 

Strathead

Senior Member
A lot of houses have isolated grounds in them by nature of the wiring methods. If you use NM and PVC boxes for a kitchen counter top circuit you have a IG circuit.
But with just a quick surface thought (no research) I don't think you could put an IG receptacle on the circuit and it would only be an IG if the house had only one panel and the neutral and ground bond point was in that panel. Regarding the IG receptacle, I guess you could use one, but only if you used non-metallic screws for a plastic or nylon cover plate, technically, because the yoke and the screw could become energized similar to the old light switches with no ground screw.
 

Strathead

Senior Member
I understand what an IG is I just didn't know if you can have multiple receptacles on one circuit and if that circuit could be in more than one room.
As you stated, I believe IG's are basically voodoo. As such, I suggest you don't overthink it. I think of the IG ground wiring as more similar to another separate neutral, common or grounded conductor (your choice of the term) system than another ground wire, with the one exception that it can "share" circuits of the same phase as well as circuits from separate phases. When you think of it this way, you can see that basically you need one and only one IG with proper current carrying capacity, in any physical "branch" of an electrical distribution run. Does that make sense?
 

GerryB

Senior Member
An IG is not one wire. Basically it's the same as a regular EGC it's just not pig tailed to any metal junction boxes or any sub-panel EGC buss bars, kinda like getting in the car pool lane on the freeway while all the other cars are stuck in that stop and go traffic.

A lot of houses have isolated grounds in them by nature of the wiring methods. If you use NM and PVC boxes for a kitchen counter top circuit you have a IG circuit.
I thought the isolated ground devices the green screw wasn't connected to the device yoke, wouldn't be the case in the kitchen, right?
 

Smart $

Esteemed Member
Location
Ohio
I thought the isolated ground devices the green screw wasn't connected to the device yoke, wouldn't be the case in the kitchen, right?
He's talking about regular receptacles, NM wiring, plastic boxes, wood framing, i.e. everything non-conductive other than the wiring... which makes the ground isolated.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I thought the isolated ground devices the green screw wasn't connected to the device yoke, wouldn't be the case in the kitchen, right?
That's correct, but if you used an NM cable with a plastic box and standard device the EGC would be isolated because it's only connected to the device.
 

tsparks1

Member
Location
Oxford
IG Rec are only part of the wiring. If you have multiple IG rec. the device grounds are put on an isolated ground bar then grounded to EGC. This is very popular on computer circuits around super computers.


Sent from my iPhone using Tapatalk
 

cuba_pete

Senior Member
Location
Washington State
No magic

No magic

It's not voodoo, it's basic electrical/electronic theory, i.e., Kirchoff's law:

At any node in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node.

Unless the single-point ground system utilizing the isolated grounding receptacles is effected as an entire system then, yes, it is not going to do much good in eliminating ground loops and/or circulating currents. It really doesn't do much for most residential installs unless equipment with a sensitivity is installed.

IEEE Green and Emerald have great explanations of this.
 

jumper

Senior Member
. I have used 12-3 mc, stripped the red insulation off at the connector for the regular egc and used the green for the isolated ground in a pinch.
What!!!

Don't you know that the lands will fall, the seas will rise, and the heavens will be torn asunder for such an action?

That conductor is smaller than #4 and all laws of physics are thrown out the window. The NEC says so.:D
 

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
What!!!

Don't you know that the lands will fall, the seas will rise, and the heavens will be torn asunder for such an action?

That conductor is smaller than #4 and all laws of physics are thrown out the window. The NEC says so.:D
Only if you put tape on the insulation. That will cause all your children to be born clothes-less and money-less. I was careful and got rid of the insulation. It's the only safe thing to do.
 

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
Your kids were born with cloths on? :blink:
I don't know, they could have been. To tell the truth my goal was to stay as far away from the action as I could. Stressful situations are bad enough; combine it with bodily fluids and unchecked emotion and all I wanted was out.... Nobody there would let me out of the room so I stayed at the head of the bed holding my wife's hand.
 
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