Isolated Ground Receptacles

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victor.cherkashi

Senior Member
Location
NYC, NY
Office space 3000 sq.ft., new tenant wants us to provide them isolated ground receptacles (furniture system workstations in open area).
I plan to run two EGC in conduit to workstations.
1. Green for regular purposes (grounding all metal parts, etc)
2. Green with yellow stripes from isolated ground terminal of furniture power whip to …? Here is question.

250.146(D) is connected to exception in 408.40. I can’t understand is it mandatory to connect the isolated EGC to applicable service or derived system, or it is just permitted (optional) ?
The office space is on 11th floor, the building distribution system is 120/208V 4000A, ConEdison service at basement. I don’t want to run one isolated EGC from 11th floor to service at basement just for this furniture system.

In case it is not mandatory (run the isolated EGC to the basement), I will connect the isolated EGC to grounding bus in tenant panel.
 
mopowr steve

mopowr steve

Senior Member
Location
NW Ohio
Occupation
Electrical contractor
Yes mandatory, has to connect to buss bar attached to GEC.

convince them that it’s just snake oil and that it’s been shown not to have any benefit.
 
T

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
victor.cherkashi said:
Office space 3000 sq.ft., new tenant wants us to provide them isolated ground receptacles (furniture system workstations in open area).
I plan to run two EGC in conduit to workstations.
1. Green for regular purposes (grounding all metal parts, etc)
2. Green with yellow stripes from isolated ground terminal of furniture power whip to …? Here is question.

250.146(D) is connected to exception in 408.40. I can’t understand is it mandatory to connect the isolated EGC to applicable service or derived system, or it is just permitted (optional) ?
The office space is on 11th floor, the building distribution system is 120/208V 4000A, ConEdison service at basement. I don’t want to run one isolated EGC from 11th floor to service at basement just for this furniture system.

In case it is not mandatory (run the isolated EGC to the basement), I will connect the isolated EGC to grounding bus in tenant panel.
Click to expand...

I don't believe the NEC actually requires you to carry it back to the service or SDS. However, to not do it defeats the purpose of an IG system and renders them pointless.
Then there is the argument about whether they provide any value even if done properly. Also, is your furniture system factory wired for IG?
I've have over the years seen a ton of IG receps that are improperly done and worthless as an IG.
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
victor.cherkashi said:
Office space 3000 sq.ft., new tenant wants us to provide them isolated ground receptacles (furniture system workstations in open area).
I plan to run two EGC in conduit to workstations.
1. Green for regular purposes (grounding all metal parts, etc)
2. Green with yellow stripes from isolated ground terminal of furniture power whip to …? Here is question.

250.146(D) is connected to exception in 408.40. I can’t understand is it mandatory to connect the isolated EGC to applicable service or derived system, or it is just permitted (optional) ?
The office space is on 11th floor, the building distribution system is 120/208V 4000A, ConEdison service at basement. I don’t want to run one isolated EGC from 11th floor to service at basement just for this furniture system.

In case it is not mandatory (run the isolated EGC to the basement), I will connect the isolated EGC to grounding bus in tenant panel.
Click to expand...

The only thing mandatory is that the IG be somehow connected just like a regular old EGC. Where this connection is made is a design choice. I would do what you've proposed in the tenant panel unless told (and paid) to do otherwise. Bottom line is no one will ever know the difference.
 
V

victor.cherkashi

Senior Member
Location
NYC, NY
texie said:
I don't believe the NEC actually requires you to carry it back to the service or SDS. However, to not do it defeats the purpose of an IG system and renders them pointless.
Then there is the argument about whether they provide any value even if done properly. Also, is your furniture system factory wired for IG?
I've have over the years seen a ton of IG receps that are improperly done and worthless as an IG.
Click to expand...

Yes, 2+2 Maxon furniture system has two utility and two IG circuits.
https://www.maxonfurniture.com/site.../2018_maxon_pricebook_q1_web_03.27.18_opt.pdf

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B

Bigjabe

Member
Location
Vancouver BC
mopowr steve said:
Yes mandatory, has to connect to buss bar attached to GEC.

convince them that it’s just snake oil and that it’s been shown not to have any benefit.
Click to expand...

Absolutely. I was told this by my boss on my first job. 13 years later I've never installed an IG receptacle and have never had a problem. This is including on industrial control systems.
 
brantmacga

brantmacga

Señor Member
Location
Georgia
Occupation
Former Child
It’s usually just the engineer’s design spec that says they want it back to the main bonding point. You don’t have to though.


Sent from my iPhone using Tapatalk
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
brantmacga said:
It’s usually just the engineer’s design spec that says they want it back to the main bonding point. You don’t have to though.
Click to expand...

Yup, it's a design issue not a code issue. You are required to have an EGC with the circuit conductors if you want to isolate that all the way back to the MBJ point at the service you may but the NEC does not require it. If you bid the job according to the design then IMO you need to follow what the engineer designed as long as you end up with something that's code complaint.
 
JoeStillman

JoeStillman

Senior Member
Location
West Chester, PA
As stated above, IG receptacles are snake oil. IEEE orange book says they are a waste of money when connected to systems with EGC's all the way back to the GE system.

They may have served a purpose at one time, before EGC's were commonly used. EMT raceway grounding and AC cable sheaths didn't always have connections as reliable as EGC's.

Electronic device engineers have made great strides since those days too. They've even learned not to call the neutral a ground!
 
kingpb

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
Unless it was missed in the bid, why wouldn't you run it? If it's spec'd or called out and you don't, you could be on the hook later when it is found out and cost a lot more to install and cost will be out of contractors pocket.
 
kwired

kwired

Electron manager
Location
NE Nebraska
texie said:
I don't believe the NEC actually requires you to carry it back to the service or SDS. However, to not do it defeats the purpose of an IG system and renders them pointless.
Then there is the argument about whether they provide any value even if done properly. Also, is your furniture system factory wired for IG?
I've have over the years seen a ton of IG receps that are improperly done and worthless as an IG.
Click to expand...
And if you truly want to have isolated ground to each IG recep, you would need to run individual grounding conductor from each one to whatever point is deemed acceptable as the common grounding point. If that is 11 floors down then you may have to run several individual conductors to a point 11 floors down, one common conductor down isn't exactly isolated in the strictest interpretations.
 
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
kwired said:
And if you truly want to have isolated ground to each IG recep, you would need to run individual grounding conductor from each one to whatever point is deemed acceptable as the common grounding point.
Click to expand...
I've never gone to that extreme. I use a separate conductor for each circuit, run with the circuit conductors.
 
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