ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Top Posters(30 Days)
sparky 5
Recent Posts
Dimmable LED 2x4 lay in fixtures
by ghost307. 12/15/17 08:13 AM
2017 NEC Changes
by ghost307. 12/15/17 08:09 AM
Casino Wiring methods
by HotLine1. 12/09/17 10:44 AM
Ground wire Size to water Line.
by HotLine1. 12/05/17 12:11 PM
Flexible conduit to an outside Spa
by gfretwell. 12/05/17 12:28 AM
New in the Gallery:
Gallery Test
Popular Topics(Views)
243,062 Are you busy
179,501 Re: Forum
170,422 Need opinion
Who's Online Now
0 registered members (), 12 guests, and 9 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
#121802 - 08/22/05 11:00 PM Return Ground Path  
Admin  Offline

Joined: Oct 2000
Posts: 3,460
What would be the danger of leaving the conduit(emt), connected to a panel with a feed from another source?

[Linked Image]

Tools for Electricians:

#121803 - 08/23/05 11:55 AM Re: Return Ground Path  
RSmike  Offline
Joined: Nov 2002
Posts: 134
Holland, MI USA
Are we talking about mixing wyes and deltas in this little diagram?? And how is this thing all grounded/bonded?? Generator transfer switch??

This isn't my area of expertise so I need more hints....


#121804 - 08/24/05 05:55 PM Re: Return Ground Path  
richard  Offline
Joined: Aug 2003
Posts: 95
L.I. New York
The generator is 480 volt to a transfer switch, then to a disco, which feeds a step down transformer (step down to 3 phase 208/120 volt) with the neutral coming off the x-o lug of the transformer. The customer wants to refeed an existing panel off the generator panel and abandon the existing feed(when all is ok with the poco feed the generator is on standby, and when they lose power the generator kicks on). my question is this, If I leave the emt connected to the existing panel, will I be creating a hazard(since there will be two ground paths going back to the main switchgear?

#121805 - 08/24/05 09:03 PM Re: Return Ground Path  
winnie  Offline
Joined: Sep 2003
Posts: 649
boston, ma
I presume that you are asking about leaving the EMT connected, but that the feeder (and thus any ground/neutral bond upstream of the feeder) will be disconnected.

I don't believe that this will result in any significant hazard, and don't believe that there is any code violation. What you will be leaving is a loop structure in the non-current carrying bonded metal. While this is a violation in current carrying conductors (unintentional parallel paths, parallel paths through equipment grounding conductors, neutral to ground fault, etc.), it is expected in non-current carrying metal.

The only time in code where loop paths are to be avoided in conduit systems are when current carrying conductors are not carried in the same conduit as their 'anti-parallel' conductors (I'm trying to come up with a general term for the complete set of conductors comprising a circuit which carry net balanced current. Loop paths that include unbalanced current carrying conductors become transformer secondaries, and can carry considerable current.

Only in some rather specific examples (MRI rooms, certain communications facilities, etc.) is a particular attempt made to insure proper star grounding with no loops, and this is not a considered a safety issue, but a design issue.

I suppose that in an environment with particularly strong and changing magnetic fields, closed paths in the conduit system could become a safety hazard; this is the issue with unbalanced current carrying conductors, but it might be an issue with high field magnets for research.


#121806 - 08/25/05 10:01 PM Re: Return Ground Path  
Larry Fine  Offline
Joined: Feb 2005
Posts: 693
Richmond, VA
"I'm trying to come up with a general term for the complete set of conductors comprising a circuit which carry net balanced current."

How about "all phases and neutral", or APAN for short?

Larry Fine
Fine Electric Co.

#121807 - 08/26/05 12:20 AM Re: Return Ground Path  
Admin  Offline

Joined: Oct 2000
Posts: 3,460
more photos...

[Linked Image]

[Linked Image]

[Linked Image]

[Linked Image]

Member Spotlight
Posts: 47
Joined: March 2008
Show All Member Profiles 

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: 0.015s Queries: 14 (0.004s) Memory: 0.7791 MB (Peak: 0.9267 MB) Zlib enabled. Server Time: 2017-12-15 23:29:21 UTC