swapping circuits

[eastcreek]

List,

I'm in a situation that requires my moving 4 circuits from a panel that is not connected to the back up gen-set. The panel I wish to move them to, is about 6' away and on a _seperate_ seperatly derived system. I cannot move the neutrals along with the line conductors for 3 of these circuits, due to sharring and only 4 available curcuits spaces in the go-to panel. Both panels are 120/208 3 phase.

I've taken voltage and frequency readings between line and nuetral of the 2 panels and things appear to be ok. I realize that not having the nuetral with 3 of the 4 circuits could could some (slight?) overheating of the conduit depite only 6' extra length of line conductor. Anyone have any concerns besides my self?

 

[don_resqcapt19]

Re: swapping circuits

There are issues with that. First there is a violation of 300.3(B) and second these systems do not share a common grounded conductor. You would be forcing the grounded conductor current to flow on the equipment grounding conductors or grounding electrode conductors to get to its source. The power from one SDS must return to that SDS, it cannot go to the grounded conductor of a second SDS.
Don

 

[bennie]

Re: swapping circuits

Although this may be a bit unconventional, technically the circuit should perform normally.

Both power sources must have a common neutral.

[ April 15, 2004, 11:47 AM: Message edited by: bennie ]

 

[ryan_618]

Re: swapping circuits

I agree with Don at this one.

 

[hurk27]

Re: swapping circuits

I cannot move the neutrals along with the line conductors for 3 of these circuits, due to sharring

You can not leave the neutrals in one panel that is shared with another circuit in another panel.

210.4 Multiwire Branch Circuits.
(A) General. Branch circuits recognized by this article shall be permitted as multiwire circuits. A multiwire branch circuit shall be permitted to be considered as multiple circuits. All conductors shall originate from the same panelboard.

 

[iwire]

Re: swapping circuits

eastcreek, you have run into one of downfalls of multiwire branch circuits.

I run multiwire branch circuits quite often, but if you need to make changes they can be a problem.

 

[don_resqcapt19]

Re: swapping circuits

bennie,

Although this may be a bit unconventional, technically the circuit should perform normally.
Both power sources must have a common neutral.

I agree that the circuit will work, but it will result in a code violation and current on the EGCs or GECs. The two transformer secondaries do not have a "common neutral". The neutrals are connected or bonded by the GECs or EGCs. These conductors are not intended to be current carrying conductors.
Don

 

[bennie]

Re: swapping circuits

Don: You are probably correct, but I don't see a violation when the multi circuit neutral is T tapped and run to the other transformer.

As stated before, the current will return to it's own source.

 

[don_resqcapt19]

Re: swapping circuits

Bennie,
What about the violation of 300.3(B). The grounded conductor is one of the circuit conductors and will not be run with the other circuit conductors.
I don't understand what you mean by "multi circuit neutral is T tapped and run to the other transformer". The neutrals of two transformers won't be T tapped, they will be connected by the grounding electrode conductors and equipment grounding conductors.
Don

 

[ed downey]

Re: swapping circuits

Eastcreek, Is This An Article 700, 701, or 702 Emergency Generator. This Could Also Affect The Fact That If It Is A Article 700 Emergency System You Will Not Be Able To Have These Emergency Circuits In The Same Conduit As The Normal Power System.
-Ed

 

[bennie]

Re: swapping circuits

The way I read this is; a single circuit(L-1) is on transformer #1. Another circuit(L-2) is fed from the transformer #2.

The neutrals join at one point to feed the circuits with one N conductor. When the neutral is again tapped to feed the load equipment, it is a reverse of the original.

The same neutral is in with the circuits when one or two wires are present.

As I stated; This in unorthodox but does not appear a safety problem to me.

I could be missing something.

[ April 16, 2004, 01:08 PM: Message edited by: bennie ]

 

[eastcreek]

Re: swapping circuits

Ed: This is a 702 arrangement.

Bennie: The senerio you describe, I assume, is the arrangment that would result if 1 line condutor on a shared 3 conductor, 1 neutral grouping, (4 wires) were moved to a panel on a seperate SDS.
It sounds as if your saying simply bond both neutrals together in the panels by running one neutral with the circuit to be moved. This seems to clear up the violation of 300.3 B and 210.4 It seems to also eliminate any posibility of current in the GEC and EGC. Is this a violation of any other code section?

 

[eastcreek]

Re: swapping circuits

BOTH PANEL NEUTRAL BARS THAT IS....

 

[don_resqcapt19]

Re: swapping circuits

eastcreek,
Bonding the grounded conductors together will result in a violation of 250.30(A)(1). It would produce two points of bonding for each of the transformers.

Ed,
If you have time one of your fantastic drawings would be very helpful here.

Don