ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Top Posters(30 Days)
twh 3
Recent Posts
FPE in Germany
by Texas_Ranger. 11/19/17 07:30 AM
Ceiling fan distance from outdoor hot tub
by gfretwell. 11/16/17 02:18 AM
diazed fuses
by Texas_Ranger. 11/13/17 03:02 PM
Theft deterrent alarm
by gfretwell. 11/12/17 01:39 PM
EEPROM errors on XC7Z010-2CLG225I chip
by twh. 11/07/17 05:45 PM
New in the Gallery:
Gallery Test
Popular Topics(Views)
242,589 Are you busy
178,761 Re: Forum
170,028 Need opinion
Who's Online Now
0 registered members (), 13 guests, and 12 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
#174758 - 02/13/08 12:45 AM IG circuits  
sudsy4  Offline
Member
Joined: Apr 2002
Posts: 32
Elizabeth,PA USA
If you have IG circuits 1, 3, and 5 from a 120/208V panel, can you share neutrals and do you need one IG conductor or three IG conductors?

Thanks for the help


Bill

Tools for Electricians:

#174766 - 02/13/08 06:44 AM Re: IG circuits [Re: sudsy4]  
SteveFehr  Offline
Member
Joined: Mar 2005
Posts: 1,213
Chesapeake, VA
Assuming circuits 1, 3 & 5 are different single-phase breakers on 3 phases & yoked together, yes, you can share the neutral (it's desireable to do so) and generally the IG. Either way is legal by code, but more of a design issue- you can share the neutral but not the IG and vice-versa.

Whether or not you want to share the IG between the equipment really depends on the equipment- if it's related equipment, it's probably OK (often desireable, especially with interconnected electronic equipment that define hi/lo communications signal from the shared IG and can really get messed up from ground loops), but sometimes equipment has specific requirements that dictate it gets a dedicated IG.


Last edited by SteveFehr; 02/13/08 06:46 AM.

#174797 - 02/14/08 01:53 AM Re: IG circuits [Re: SteveFehr]  
sudsy4  Offline
Member
Joined: Apr 2002
Posts: 32
Elizabeth,PA USA
Code is not an issue. The equipment is mostly cash registers and related equipment (scanners, etc.) , approximately 75 devices with 3 or 4 per circuit.


Bill

#174798 - 02/14/08 02:39 AM Re: IG circuits [Re: SteveFehr]  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,708
Anaheim, CA. USA
I would begin with the typical disclaimers:

* What is specified on the Contract Documents,
* What was written in the Proposal.

If a certain wiring configuration was specified and bid as, then install per the scope.

If these circuits are "Design Per Suggestions" (client is asking you to perform best install), then you have many options - including suggesting to NOT use IG Circuitry.

Computer equipment - such as Workstations and most Servers, really do not need the extra expense of IG Circuitry - and at times, if done incorrectly, may add problems rather than benefits.

Audio / Video Circuitry may have certain benefits from the use of IG Circuitry, in order to reduce loop currents which cause audible and visual noise.

Having said that, here are some key items regarding IG Circuitry...

1: "Intent Of Design"
The intent of the IG Circuit is to have a "Dedicated" Equipment Grounding Conductor for _EACH OUTLET_, which terminates at the "Star Point" of the System's Grounding point.

This results in the IG Conductors all terminating to a bus, where the System's Bonding Jumper, Grounded Conductor, Equipment Grounding Conductors and Grounding Electrode Conductors all terminate.
Could be at the Main Service, or at a Transformer - all depends on what System is used.

The target goal of this approach is to have _ALL_ the bonding Conductors + connections to Earth at the same point - hence the same potential; which eliminates excessive circulating current in the Conductors which are Ground Bonded.

From the description above, one may see why the NEC allows these supplementary Isolated Equipment Grounding Conductors to run through Panelboards, as necessary, to get to the "Star Point" Grounding connection - without having to be bonded to each Panelboard or other type enclosure.

2: "Per NEC Minimum"
To be NEC compliant, an IG Circuit may be as simple as any 2 Wire circuit, connected to an IG Receptacle, where the Ground terminal has a jumper bonded right to the outlet box.

That satisfies the minimum NEC requirement - as it should be a safe installation.
Article 90 clearly states the NEC cares nothing of overall performance, as these are the magic word "DESIGN ISSUES".
The installation could suck big time, as far as performance - just as long as it is installed safe.

3: "Sharing the Common Grounded Conductor"
If the Multiwire Circuit is going to be driving similar loads in the same general area (nothing with an odd running characteristic which would result in heavy noise &/or sporadic on/off switch surges), then share the Common Grounded Conductor - AKA "Neutral".
You will be "Balancing" 2 or 3 L-N Circuits across "Opposing Phases" as usual.

Unless there are some prearranged specifications which absolutely demand the use of Dedicated 2 wire Circuitry - or for some odd reason, a very noisy piece of equipment is to be connected to the Multiwire Circuit, I suggest to use a "Balanced Neutral" technique.
In your example, Circuits 1, 3 and 5 sharing a single, common Grounded Neutral Conductor.

4: "IG Circuitry - Target Goal Method #1"

Let's say there are Three (3) individual 4-plex (Double Duplex) IG Receptacles to connect, each 4-plex is driven by a "Dedicated" 20 Amp Circuit, as described below:
A: One Receptacle on Circuit #1 (Phase A),
B: One Receptacle on Circuit #3 (Phase B),
C: One Receptacle on Circuit #5 (Phase C).

To design within the "Intended Target Goal", each Duplex Receptacle would have a Dedicated IG Conductor run from it, to the Star Grounding Point.
This would result in a Homerun consisting of:
* Six (6) IG Conductors,
* Three (3) Ungrounded (Hot) Conductors,
* One (1) Grounded Neutral Conductor,
and if wanted,
* One (1) Equipment Grounding Conductor.

From a common junction box, each 4-plex Receptacle would be fed with Two IGs, One Hot, One Common Neutral, and One Equipment Ground.

5: "Landing The IGs"

As mentioned before, the Ideal location to land the IG Conductors is on a bus at the "Star Point" for the System's Grounding.

If this is not feasible, a single IG "Feeder" may be run from that Star Point, to the Panelboard which the IG Circuits are derived from, and landed to an Isolated Grounding bus in that Panelboard (Isolated from the metallic enclosure).
Then all the IG Branch Circuit Conductors terminate to that IG bus in the Panelboard
(*** "Panelboard" = "Sub Panel")

6: "If The IG Circuits Are Not Driving Critical Equipment"
If these proposed IG Circuits are just driving typical desktop Computer Workstation equipment, then you may go as far as just running a single IG Conductor to each 4-plex Receptacle - with a total of Three (3) IG Conductors, Three Hots, One Grounded Neutral, and One Equipment Ground.

Heck, if there are no specs, and $$$ is the primary motivation, go with only One IG Conductor for all 3 Circuits!

Like I said, the IG concepts really have no benefit for modern Computers, *** UNDER MOST CONDITIONS ***
There are some specific conditions, which would require IG Circuitry - these installations would have clearly defined specifications regarding the use and installation of IG Circuitry, of which it was very apparent things were Engineered and documented specifically for that project, not just some "Boiler Plate" text, or "It's Gotta Be IG" statements thrown around.

OK, Soapbox Mode = OFF

Let's hear from you - what are your thoughts?

Scott


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#175041 - 02/20/08 01:02 PM Re: IG circuits [Re: Scott35]  
sudsy4  Offline
Member
Joined: Apr 2002
Posts: 32
Elizabeth,PA USA
* Six (6) IG Conductors,
* Three (3) Ungrounded (Hot) Conductors,
* One (1) Grounded Neutral Conductor,
and if wanted,
* One (1) Equipment Grounding Conductor.


That's the way we did it.

Thanks


Bill

#175272 - 02/26/08 04:13 AM Re: IG circuits [Re: sudsy4]  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,708
Anaheim, CA. USA
sudsy4

Thanks for the reply.

Scott


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!


Member Spotlight
MarkC10
MarkC10
CA, Inland Empire
Posts: 43
Joined: September 2013
Show All Member Profiles 
Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.016s Queries: 15 (0.003s) Memory: 0.7818 MB (Peak: 0.9292 MB) Zlib enabled. Server Time: 2017-11-20 13:14:12 UTC