Isolated ground / EMT

Charged

Member
Location
Ohio
Occupation
Electrical Designer
If I have branch circuits utilizing A combination of EMT and MC cable wiring methods and I always specify the MC to have a separate ground conductor and my circuits all have a equipment grounding conductor, are all these circuits considered to have a isolated ground conductor ?

I guess the questions is if you use EMT is it always installed to qualify as a equipment ground or as a contractor would that change the way you install it if you you knew it needed it to be?
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
Unless the two egc's (wire and conduit) are completely separated from point to point you have redundant egc's, the same as 517.13 requires
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
If I have branch circuits utilizing A combination of EMT and MC cable wiring methods and I always specify the MC to have a separate ground conductor and my circuits all have a equipment grounding conductor, are all these circuits considered to have a isolated ground conductor ?
No, what you have described is not an isolated ground system. If you put an EGC is the EMT you'll have redundant grounding not isolated grounding.
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
Do you mean like in a wood framed building using NM-B non-metallic cable?
If it is a dedicated NM circuit run straight to a plastic box at the end it would be a true isolated ground, you wouldn't even need an isolated ground receptacle.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
If it is a dedicated NM circuit run straight to a plastic box at the end it would be a true isolated ground, you wouldn't even need an isolated ground receptacle.
Good point. If the individual branch circuit originates at the service the EGC would terminate at the same point as where the MBJ is installed making it for all intents and purposes an IG.
 

kwired

Electron manager
Location
NE Nebraska
If I have branch circuits utilizing A combination of EMT and MC cable wiring methods and I always specify the MC to have a separate ground conductor and my circuits all have a equipment grounding conductor, are all these circuits considered to have a isolated ground conductor ?

I guess the questions is if you use EMT is it always installed to qualify as a equipment ground or as a contractor would that change the way you install it if you you knew it needed it to be?
As mentioned the isolated ground thing is mostly a dinosaur, but if you were intending to have one, the MC cable portion would need to contain a wire type EGC as well as be designed for the cable sheath to qualify as an EGC. A HCF rated assembly fits the requirement but regular MC cable is not listed for sheath to be used as an EGC.
 

Charged

Member
Location
Ohio
Occupation
Electrical Designer
If the raceway qualifies as a EGC and the sep””wire type ground conductor gets back to the source or an isolated ground bar in the panel (that’s set up correctly) does that cover it. In the op I didn’t clarify what the wire type egc was doing so it was mentioned it was just a redundant ground , does that sound right ?
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
If the raceway qualifies as a EGC and the sep””wire type ground conductor gets back to the source or an isolated ground bar in the panel (that’s set up correctly) does that cover it. In the op I didn’t clarify what the wire type egc was doing so it was mentioned it was just a redundant ground , does that sound right ?
If the raceway qualifies as an egc and the wire type EGC connects only to the isolated ground receptacle you have an isolated ground circuit. The raceway will satisfy the bonding requirements of 250.4 and the wire will be for the receptacle by itself.

So yes, you are correct that it covers it.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
If the raceway qualifies as a EGC and the sep””wire type ground conductor gets back to the source or an isolated ground bar in the panel (that’s set up correctly) does that cover it. In the op I didn’t clarify what the wire type egc was doing so it was mentioned it was just a redundant ground , does that sound right ?
Yes that sounds correct. A true IG system would have to be designed and installed as one. That would include the IG receptacle, two EGC's in the branch circuit, and an IG system at the source.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
The IG conductor is effectively treated as a grounded conductor. It must be insulated. Every device, joint, and termination must be isolated from any grounding conductor, conduit, or other grounded surface.

It starts at the IG receptacle(s), whose grounding terminal is isolated from the yoke, through any boxes and/or panels insulated from any grounding, and only terminates where the main bonding jumper does.
 
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